//! The command files and the status they answer. Writing a line to `look` is
//! a right click on it and writing one to `exec` a middle click, at the
//! active pane from the root and at that pane from /pane/<n>/; reading either
//! answers the serials the last command made or touched. /status reports the
//! editor. The root ctl reads the settings and takes the session's builtins;
//! a pane's ctl reads its acme status line and takes acme's verbs `get`,
//! `lock` and `unlock` and the builtins that act on a pane.
const std = @import("std");
const pardes = @import("../pardes.zig");
const look = @import("../look.zig");
const panes = @import("../panes.zig");
const config = @import("../config.zig");
const fs = @import("../fs.zig");
const tagline = @import("../tagline.zig");
const layout = @import("../layout.zig");
const builtins = @import("../builtins.zig");
const exec_line = @import("../exec.zig");
const tree = @import("tree.zig");
const pane_files = @import("pane.zig");

const Pardes = pardes.Pardes;
const Pane = pardes.Pane;
const MAX_PANES = pardes.MAX_PANES;
const Req = tree.Req;
const Reply = tree.Reply;
const E = tree.E;

// ---- which panes a command made or touched ----

const Serials = struct {
    list: [MAX_PANES]u32 = undefined,
    len: usize = 0,

    fn snapshot(p: *Pardes) Serials {
        var s: Serials = .{};
        for (p.panes) |slot| if (slot) |pane| {
            s.list[s.len] = pane.serial;
            s.len += 1;
        };
        return s;
    }
};

fn noteResult(p: *Pardes, serial: u32) void {
    for (p.fs.results[0..p.fs.results_len]) |known| if (known == serial) return;
    if (p.fs.results_len == p.fs.results.len) return;
    p.fs.results[p.fs.results_len] = serial;
    p.fs.results_len += 1;
}

/// Runs one look or exec from the pane `id`, then records the panes it
/// created; failing that, a look records the pane it focused and an exec
/// the pane it acted on (even one it closed).
pub fn run(p: *Pardes, id: usize, exec: bool, text: []const u8, in_tag: bool) void {
    const context = if (p.panes[id]) |pane| pane.serial else 0;
    // A pane an event reader holds hears its clicks instead of acting on
    // them (editors/acme/look.c:53 and exec.c:173 send them to winevent),
    // and a line written to a look or exec is a click: on that pane, or for
    // the root's, on the pane with the keyboard. The reader writes the
    // record back to have it done.
    // A click in a column's or the workspace's tag is not the pane's; one
    // in the pane's own tag (its tagexec) is, an `x` or `l` record as
    // acme's tag clicks are.
    if (!p.exec_header and p.panes[id].?.fs.readers > 0) {
        const named = exec_line.namesBuiltin(text);
        // No flag 2: a written line was never expanded from a click, and no
        // expansion record follows (editors/acme/look.c:42-43, exec.c:154-157).
        var flag: u32 = 0;
        if (named) flag |= pardes.ctlfs.events.flag_builtin;
        if (!exec and !named and std.mem.indexOfAny(u8, text, "/.:") != null) flag |= pardes.ctlfs.events.flag_filename;
        const action: pardes.ctlfs.events.Action = if (in_tag)
            (if (exec) .tag_exec else .tag_look)
        else
            (if (exec) .body_exec else .body_look);
        _ = pardes.ctlfs.events.noteAction(p, id, action, 0, 0, flag, text);
        return noteResult(p, context);
    }
    const before = Serials.snapshot(p);
    // An exec answers the pane it went to: a command pane it reused, or
    // the terminal it typed into.
    p.look_missed = false;
    p.fs.refilled = null;
    const went: ?usize = if (exec) pardes.exec.execute(p, id, text) else blk: {
        look.lookAt(p, id, text);
        break :blk null;
    };
    // A look that found nothing answers nothing, not the pane before it.
    if (!exec and p.look_missed) return;
    const after = Serials.snapshot(p);
    var created = false;
    for (after.list[0..after.len]) |serial| if (std.mem.indexOfScalar(u32, before.list[0..before.len], serial) == null) {
        // A look that made a +Search pane (LookWord list, a terminal)
        // answers it: that is where the places it found are.
        noteResult(p, serial);
        created = true;
    };
    if (created) return;
    // A +Search it filled again (Find and Grep reuse one): that is what it
    // touched.
    if (p.fs.refilled) |serial| if (p.paneBySerial(serial) != null) return noteResult(p, serial);
    if (went) |dst| if (p.panes[dst]) |pane| return noteResult(p, pane.serial);
    // A word in a column's or the workspace's tag ran at no pane: it
    // answers one only if it focused one (Newcol answers nothing).
    if (p.exec_header) {
        if (p.active != id) if (p.panes[p.active]) |pane| noteResult(p, pane.serial);
        return;
    }
    noteResult(p, if (exec) context else (p.panes[p.active] orelse return).serial);
}

/// A write's messages, a line each, except that an `Edit` line takes the
/// lines after it while its `{` group or `a`/`c`/`i` text block is open
/// (sam_edit.needsMore): a block written whole reaches Edit whole, never
/// as lines of their own.
const Messages = struct {
    p: *Pardes,
    data: []const u8,
    at: usize = 0,
    /// A look's line is its text, leading blanks and all (`    return x`,
    /// a diff's context line ` ` alone): only its `\r` goes.
    keep_blanks: bool = false,

    fn init(p: *Pardes, data: []const u8) Messages {
        return .{ .p = p, .data = data };
    }

    fn next(m: *Messages) ?[]const u8 {
        if (m.at >= m.data.len) return null;
        const start = m.at;
        var end = std.mem.indexOfScalarPos(u8, m.data, start, '\n') orelse m.data.len;
        m.at = end + 1;
        if (m.keep_blanks) return std.mem.trimEnd(u8, m.data[start..end], "\r");
        const first = std.mem.trim(u8, m.data[start..end], " \t\r");
        const edit = "Edit";
        if (!std.mem.startsWith(u8, first, edit) or (first.len > edit.len and first[edit.len] != ' ' and first[edit.len] != '\t'))
            return first;
        end = editEnd(m.p, m.data, start, end, true).?;
        m.at = end + 1;
        return std.mem.trim(u8, m.data[start..end], " \t\r");
    }
};

/// Where the Edit block whose first line is `data[start..first_end]` ends:
/// the end of its last line, taking the lines after it while its `{`
/// group or a/c/i text block is open. Out of lines, the end of `data` when
/// `to_end` (a write run whole), else null (wait for more). Only a line
/// that could end what is open is parsed again with all before it: within
/// a text block, just a `.` line. The arena copy of each parse is freed.
fn editEnd(p: *Pardes, data: []const u8, start: usize, first_end: usize, to_end: bool) ?usize {
    const sam = @import("../sam_edit.zig");
    const edit = "Edit";
    const arena = p.scratch.allocator();
    var end = first_end;
    var wait = sam.waitsFor(arena, std.mem.trim(u8, data[start..end], " \t\r")[edit.len..]);
    while (wait != .none) {
        if (end >= data.len) return if (to_end) data.len else null;
        const next = std.mem.indexOfScalarPos(u8, data, end + 1, '\n') orelse
            (if (to_end) data.len else return null);
        const line = std.mem.trim(u8, data[end + 1 .. next], " \t\r");
        end = next;
        if (wait == .text and !std.mem.eql(u8, line, ".")) continue;
        wait = sam.waitsFor(arena, std.mem.trim(u8, data[start..end], " \t\r")[edit.len..]);
    }
    return end;
}

/// How much of `data` is whole messages, as `Messages` reads them: lines
/// ended by a newline, an Edit block only once it closes. The rest waits
/// for more (tree.Open.pending).
pub fn completeEnd(p: *Pardes, data: []const u8) usize {
    const edit = "Edit";
    var whole: usize = 0;
    var at: usize = 0;
    while (std.mem.indexOfScalarPos(u8, data, at, '\n')) |nl| {
        const start = at;
        var end = nl;
        const first = std.mem.trim(u8, data[start..end], " \t\r");
        if (std.mem.startsWith(u8, first, edit) and (first.len == edit.len or first[edit.len] == ' ' or first[edit.len] == '\t'))
            end = editEnd(p, data, start, end, false) orelse return whole;
        at = end + 1;
        whole = at;
    }
    return whole;
}

// ---- look and exec ----

/// One command per line, checked whole before any line runs: a line is the
/// clicked text itself, so it may not be empty or carry control characters.
/// A null `serial` clicks at whichever pane is active as each line runs,
/// which is what the root's own look and exec mean; a serial stays put.
pub fn command(p: *Pardes, req: Req, serial: ?u32, exec: bool, in_tag: bool) Reply {
    // The root's lines run at the keyboard's pane: a refusal before any runs
    // is that pane's too, in its err record.
    p.fs.ran_at = if (serial == null) (if (p.panes[p.active]) |pane| pane.serial else 0) else 0;
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var it = Messages.init(p, req.data);
        it.keep_blanks = !exec;
        while (it.next()) |text| {
            if (text.len == 0) continue;
            // Only an Edit block holds newlines (Messages).
            for (text) |c| if ((c < ' ' and c != '\t' and c != '\n') or c == 0x7f) return tree.failText(req.tag, E.INVAL, e_control);
            if (exec) if (tooLong(req, text)) |refusal| return refusal;
            if (!apply) continue;
            var id = if (serial) |s| p.paneBySerial(s) orelse break else p.active;
            // No pane at all: the root's look and exec act in the session's
            // directory. An exec runs as the workspace tag's; a look from a
            // scratch made as New makes one (and its column), dropped
            // unannounced when the look went elsewhere.
            var scratch: ?usize = null;
            if (p.panes[id] == null and serial == null and p.anyPane() == null) {
                if (exec) {
                    p.exec_header = true;
                    defer p.exec_header = false;
                    if (captured(p, req, id, exec, text, true)) |refusal| return refusal;
                    continue;
                }
                const free = p.freeSlot() orelse return Reply.fail(req.tag, E.NOSPC);
                p.newScratchFor(id, .scratch);
                if (p.panes[free] == null) return Reply.fail(req.tag, E.NOSPC);
                p.active = free;
                id = free;
                scratch = free;
            }
            if (p.panes[id] == null) return Reply.fail(req.tag, E.NOENT);
            defer if (scratch) |s| if (p.active != s) if (p.panes[s]) |sp| if (sp.file) |f| {
                if (f.content.len == 0) p.removePane(s, null) catch {};
            };
            p.fs.ran_at = p.panes[id].?.serial;
            p.fs.no_pane_slot = false;
            if (captured(p, req, id, exec, text, in_tag)) |refusal| return refusal;
            // A pane it would have opened had no slot: the write fails, and
            // a look reads back nothing.
            if (p.fs.no_pane_slot) {
                p.fs.results_len = 0;
                return tree.failText(req.tag, E.IO, p.fs.ename[0..p.fs.no_pane_slot_len]);
            }
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

// "invalid" is the word 9ns reads as EINVAL (enameToErrno): through a
// mount the refusal is EINVAL, as the reply's errno is.
pub const e_too_long = std.fmt.comptimePrint("invalid command line: a command line is at most {d} bytes", .{pardes.exec.command_max});

/// A line an exec would run as a command, over the most a command line may
/// be: refused whole, before anything runs, rather than said on the message
/// row after the write succeeded. A builtin's line (Msg, an Edit block) may
/// be longer.
pub fn tooLong(req: Req, line: []const u8) ?Reply {
    if (line.len <= pardes.exec.command_max) return null;
    const cmd = exec_line.commandText(line);
    const word = cmd[0 .. std.mem.indexOfAny(u8, cmd, " \t+") orelse cmd.len];
    if (std.meta.stringToEnum(Builtin, word) != null) return null;
    return tree.failText(req.tag, E.INVAL, e_too_long);
}

pub const e_control = "invalid command line: it holds a control character (or DEL) other than a tab";

/// Runs one click (`run`) as a 9P write's: a builtin that fails there fails
/// the write, with its words and an err record, and no msg, as a ctl line
/// does (runBuiltin). The refusal, or null.
pub fn captured(p: *Pardes, req: Req, id: usize, exec: bool, text: []const u8, in_tag: bool) ?Reply {
    // A builtin that means nothing without its argument, written bare: the
    // write is refused, EINVAL, as a ctl's is (checkBuiltin), not run to
    // fail or to ask.
    if (exec) {
        const cmd = exec_line.commandText(text);
        if (std.meta.stringToEnum(Builtin, cmd)) |b| if (builtins.registry.requiresArg(b)) {
            p.fs.results_len = 0;
            return refuse(p, req, "wrong #args in control message", cmd);
        };
        // ...and one that takes none, written with one (`Config extra`):
        // refused as a ctl's is, not run as a shell command of that name.
        if (std.mem.indexOfAny(u8, cmd, " \t")) |sp| if (std.meta.stringToEnum(Builtin, cmd[0..sp])) |b| {
            if (!builtins.registry.takesArg(b) and config.Runtime.find(cmd[0..sp]) == null) {
                p.fs.results_len = 0;
                return refuse(p, req, "wrong #args in control message", cmd);
            }
        };
    }
    p.fs.capturing = true;
    p.fs.failure_len = 0;
    defer p.fs.capturing = false;
    run(p, id, exec, text, in_tag);
    if (p.fs.failure_len == 0) return null;
    // A failed click answers nothing: look reads back empty.
    p.fs.results_len = 0;
    const failure = p.fs.failure[0..p.fs.failure_len];
    // A slot or a place refused keeps its errno words (no space: ENOSPC).
    return tree.failText(req.tag, failureErrno(failure), std.fmt.bufPrint(&p.fs.ename, "{s}", .{failure}) catch failure);
}

/// The errno a builtin's failure answers with: ENOENT for what is not
/// there (`no such`, `not found`, the words 9ns reads as ENOENT too), else
/// EIO.
pub fn failureErrno(failure: []const u8) u16 {
    if (std.mem.indexOf(u8, failure, "no such") != null or std.mem.indexOf(u8, failure, "not found") != null) return E.NOENT;
    // A pattern refused (Edit's too) is malformed input, as 9ns reads it;
    // so is a word this build has not (`invalid: acme's Put ...`).
    if (std.mem.indexOf(u8, failure, "bad regular expression") != null or std.mem.startsWith(u8, failure, "invalid") or
        std.mem.startsWith(u8, failure, "address out of range")) return E.INVAL;
    // A word's arguments wrong, or a dial that is no address: what 9ns
    // reads as EINVAL from the same words (`control message`, `bad `).
    if (std.mem.indexOf(u8, failure, "control message") != null or std.mem.indexOf(u8, failure, "bad dial address") != null) return E.INVAL;
    return E.IO;
}

pub fn resultsLen(p: *Pardes) u64 {
    var n: u64 = 0;
    for (p.fs.results[0..p.fs.results_len]) |serial| {
        var digits: [16]u8 = undefined;
        // unreachable: a u32 serial and a newline fit 16
        n += (std.fmt.bufPrint(&digits, "{d}\n", .{serial}) catch unreachable).len;
    }
    return n;
}

/// The panes the open's last write touched (tree.Open.results); with no
/// open, the session's last.
pub fn readResults(p: *Pardes, req: Req) Reply {
    const out = p.fs.stage(p.gpa);
    const o = tree.openOf(p, req);
    const kept = if (o) |open| open.results.list[0..open.results.len] else p.fs.results[0..p.fs.results_len];
    // A look answers panes to go to: never one closed since (an exec may
    // answer the pane it closed, which is what it acted on).
    const looking = if (tree.Node.target(req.node)) |t| switch (t) {
        .top => |f| f == .look,
        .pane => |pt| pt.file == .look,
        .col => false,
    } else false;
    for (kept) |serial| if (!looking or p.paneBySerial(serial) != null)
        out.print(p.gpa, "{d}\n", .{serial}) catch return Reply.fail(req.tag, E.NOMEM);
    const open = o orelse return tree.stagedReply(p, req);
    if (!open.results.wrote) return tree.stagedReply(p, req);
    var at = req;
    at.off = open.results.read;
    const reply = tree.stagedReply(p, at);
    open.results.read += reply.payload.staged;
    return reply;
}

// ---- /status ----

fn statusText(p: *Pardes, buf: []u8) []const u8 {
    var w = std.Io.Writer.fixed(buf);
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const pid: u32 = if (comptime pardes.hosted) @intCast(std.c.getpid()) else 0;
    w.print("pid {d}\nversion {s}\npanes {d}\n", .{ pid, pardes.version, count }) catch {};
    return w.buffered();
}

pub const status_text_cap = 64 + pardes.version.len;

pub fn statusLen(p: *Pardes) u64 {
    var buf: [status_text_cap]u8 = undefined;
    return statusText(p, &buf).len;
}

pub fn readStatus(p: *Pardes, req: Req) Reply {
    var buf: [status_text_cap]u8 = undefined;
    const out = p.fs.stage(p.gpa);
    out.appendSlice(p.gpa, statusText(p, &buf)) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

// ---- /pane/<n>/ctl ----

fn writeQuoted(w: *std.Io.Writer, s: []const u8) !void {
    const plain = s.len > 0 and for (s) |c| {
        if (c <= ' ' or c == '\'') break false;
    } else true;
    if (plain) return w.writeAll(s);
    try w.writeByte('\'');
    for (s) |c| {
        if (c == '\'') try w.writeByte('\'');
        try w.writeByte(c);
    }
    try w.writeByte('\'');
}

pub const pane_text_cap = 9 * 12 + 2 * 256 + 4 + "notcurrent ".len + 48;

/// acme's winctlprint (plan9port wind.c), field for field: serial, tag
/// length, body length, isdir (0), the dirty flag, the width in cells, the
/// font, the tab width, whether Undo has a step, whether Redo has one. Then
/// pardes's own: rio's word for whether the window has the keyboard,
/// `current` or `notcurrent` (rio(4), wctl), and a REPL's id.
pub fn paneText(p: *Pardes, pane: *Pane, buf: []u8) []const u8 {
    var w = std.Io.Writer.fixed(buf);
    w.print("{d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {d:>11} ", .{
        pane.serial,
        pane_files.tagOf(p, pane).len,
        // A terminal's body is its history, read whole on an open's first read.
        if (pane.isTerminal()) panes.terminal.screenTextLen(pane) else pane_files.bodyOf(pane).len,
        @as(u32, 0),
        @intFromBool(pane_files.dirtyOf(pane)),
        pane.cols,
    }) catch return w.buffered();
    const font = p.settings.font.effective_name.get();
    writeQuoted(&w, if (font.len == 0) "default" else font) catch return w.buffered();
    // While a column's or the workspace's tag has the keyboard, no pane does.
    const current = p.panes[p.active] == pane and !p.header_focus;
    const f = pane_files.fileOf(pane);
    const undo = if (f) |file| file.history.undo_len > 0 else false;
    const redo = if (f) |file| file.history.redo_len > 0 else false;
    w.print(" {d:>11} {d:>11} {d:>11} {s} ", .{ config.tab_width, @intFromBool(undo), @intFromBool(redo), if (current) "current" else "notcurrent" }) catch {};
    // A terminal bound as a REPL ends with its id, `python-a`.
    var idbuf: [48]u8 = undefined;
    const id = exec_line.replId(&idbuf, pane);
    if (id.len > 0) w.print("{s} ", .{id}) catch {};
    return w.buffered();
}

// ---- control messages: the builtins, by scope ----

const Builtin = builtins.registry.Builtin();

/// Refuses a control message, quoting it the way Plan 9's cmderror does
/// (kernel/misc/parse.c:82): `unknown control message "Bogus 3"`.
fn refuse(p: *Pardes, req: Req, why: []const u8, line: []const u8) Reply {
    return refuseQuoting(p, req, why, firstWord(line));
}

/// `refuse` quoting `word` as given: a setting's bad value, blanks and all.
fn refuseQuoting(p: *Pardes, req: Req, why: []const u8, word: []const u8) Reply {
    // A word too long to quote whole gives up its middle (fitErr), so the
    // refusal keeps both its ends.
    var shown: [4096]u8 = undefined;
    var whole: [4096 + 320]u8 = undefined;
    const full = std.fmt.bufPrint(&whole, "{s} \"{s}\"", .{ why, blanked(word[0..@min(word.len, shown.len)], &shown) }) catch why;
    // Into the session's own buffer: `whole` is this frame's.
    if (full.len <= p.fs.ename.len) {
        @memcpy(p.fs.ename[0..full.len], full);
        return tree.failText(req.tag, E.INVAL, p.fs.ename[0..full.len]);
    }
    return tree.failText(req.tag, E.INVAL, tree.fitErr(full, &p.fs.ename));
}

/// The word a refusal quotes: a control message's first, its offending
/// word, never the line with its arguments (one rule everywhere: `wrong
/// #args in control message "Newcol"`).
pub fn firstWord(line: []const u8) []const u8 {
    const trimmed = std.mem.trim(u8, line, " \t\r\n");
    return trimmed[0 .. std.mem.indexOfAny(u8, trimmed, " \t") orelse trimmed.len];
}

/// `refuse`, saying which ctl takes the message instead.
pub fn refuseTo(p: *Pardes, req: Req, why: []const u8, line: []const u8, ctl: []const u8) Reply {
    const room = p.fs.ename.len -| (why.len + ctl.len + 18);
    var shown: [320]u8 = undefined;
    const text = std.fmt.bufPrint(&p.fs.ename, "{s} \"{s}\": write it to {s}", .{ why, blanked(firstWord(line)[0..@min(firstWord(line).len, room)], &shown), ctl }) catch why;
    return tree.failText(req.tag, E.INVAL, text);
}

/// A quoted line as a refusal shows it: a control byte (a tab, the one a
/// line may hold) is a blank, so the reason reads as one line of words.
fn blanked(line: []const u8, buf: []u8) []const u8 {
    const n = @min(line.len, buf.len);
    for (line[0..n], buf[0..n]) |c, *o| o.* = if (c < ' ' or c == 0x7f) ' ' else c;
    return buf[0..n];
}

/// Checks one line written to a ctl as a builtin of `scope` before any line
/// of the write runs: a word the registry knows, of this ctl's scope, given
/// an argument if and only if it takes or requires one, and for a setting a
/// value it takes.
/// Answers the refusal, or null. Words are the builtins' own, capitalised
/// as on a tag; acme's lowercase verbs are the pane ctl's and alias none.
fn checkBuiltin(p: *Pardes, req: Req, line: []const u8, scope: builtins.Scope) ?Reply {
    var sp = std.mem.indexOfAny(u8, line, " \t");
    // `Word+arg` for a word that takes one so (`Tty+bash`), as exec does.
    if (sp == null) if (std.mem.indexOfScalar(u8, line, '+')) |at| if (std.meta.stringToEnum(Builtin, line[0..at])) |head| {
        if (builtins.registry.plusArg(head)) sp = at;
    };
    const typed = line[0 .. sp orelse line.len];
    // acme's words: checked as the pardes word they run as, or refused.
    const word = for (pardes.exec.acme_words) |w| {
        if (!std.mem.eql(u8, typed, w.acme)) continue;
        const now = w.pardes orelse return tree.failText(req.tag, E.INVAL, std.fmt.bufPrint(&p.fs.ename, "invalid: acme's {s} is not a pardes builtin{s}", .{ w.acme, w.hint }) catch "invalid: an acme word pardes has not");
        break now;
    } else typed;
    const arg = if (sp) |s| std.mem.trim(u8, line[s + 1 ..], " \t") else "";
    const b = std.meta.stringToEnum(Builtin, word) orelse {
        // A setting this build's frontend cannot show (Lift, GripWidth on a
        // terminal) is known, and says so rather than sound misspelt.
        if (builtins.absentWhy(word) orelse if (config.Runtime.find(word) != null) @as([]const u8, "GUI-only") else null) |absent| {
            var why: [64]u8 = undefined;
            // EINVAL, a request this build cannot take, in words 9ns reads
            // as that: `invalid`.
            return refuse(p, req, std.fmt.bufPrint(&why, "{s} is {s}, invalid here", .{ word, absent }) catch "GUI-only, invalid here", line);
        }
        return refuse(p, req, "unknown control message", line);
    };
    // Edit is the one pane word the root takes too: at the active pane.
    if (builtins.registry.scope(b) != scope and b != .Edit)
        return refuseTo(p, req, if (scope == .pane) "not a window control message" else "not a session control message", line, if (scope == .pane)
            "/ctl"
        else if (b == .Delcol or b == .Joincol)
            "col/<serial>/ctl" // a column's own ctl, the one /layout names
        else
            "pane/<n>/ctl");
    if (arg.len > 0 and !builtins.registry.takesArg(b)) return refuse(p, req, "wrong #args in control message", line);
    if (arg.len == 0 and builtins.registry.requiresArg(b)) return refuse(p, req, "wrong #args in control message", line);
    const setting = config.Runtime.find(word) orelse return null;
    const takes = switch (setting.action) {
        .theme => if (pardes.colors.themeIndex(arg) != null) true else {
            // `refuse` quotes the line after it, all in the 128 bytes an
            // Rerror carries: the names get what is left.
            const head = "bad value in control message; like it: ";
            const tail = "; Themes lists all";
            var near: [128]u8 = undefined;
            const room = @import("cloud9").fs.errmax -| (head.len + tail.len + line.len + 3);
            var why: [256]u8 = undefined;
            return refuse(p, req, std.fmt.bufPrint(&why, head ++ "{s}" ++ tail, .{pardes.colors.themesNear(near[0..@min(room, near.len)], arg)}) catch "bad value in control message", arg);
        },
        .font => config.Runtime.FontSpec.parse(arg) != null,
        else => probe: {
            var probe = p.settings;
            break :probe probe.apply(setting, if (arg.len > 0) arg else null);
        },
    };
    if (takes) return null;
    var why: [160]u8 = undefined;
    // The offending word is the value: quoted, so two bad values read,
    // and log, as two.
    return refuseQuoting(p, req, if (config.Runtime.takes(setting.action)) |values|
        std.fmt.bufPrint(&why, "bad value in control message; takes {s}", .{values}) catch "bad value in control message"
    else
        "bad value in control message", arg);
}

/// Runs a checked control message at pane `id`, as a click on its word
/// would. Answers the refusal when it would have opened a prompt for an
/// argument, which nobody writing to a file is there to type, or when it
/// reported an error: `Mount: AlreadyMounted "Mount peer /tmp/s"`.
pub fn runBuiltin(p: *Pardes, req: Req, id: usize, line: []const u8) ?Reply {
    p.fs.no_prompt = true;
    p.fs.refused = false;
    p.fs.failure_len = 0;
    defer p.fs.no_prompt = false;
    // What a ctl write touched reads back from /look and /exec as a click's
    // does (`run`), so a script that made a pane with `Tty` finds it there.
    const context = if (p.panes[id]) |pane| pane.serial else 0;
    const before = Serials.snapshot(p);
    _ = exec_line.executeBuiltinLine(p, id, line);
    const after = Serials.snapshot(p);
    var created = false;
    for (after.list[0..after.len]) |serial| if (std.mem.indexOfScalar(u32, before.list[0..before.len], serial) == null) {
        noteResult(p, serial);
        created = true;
    };
    if (!created) noteResult(p, context);
    if (p.fs.refused) return refuse(p, req, e_prompt, line);
    if (p.fs.failure_len == 0) return null;
    // A line that ran and failed says why in the builtin's own words, which
    // name what failed (`Mount peer /tmp/s: dial failed: ...`): the line is
    // not quoted after them, as an exec's is not. Only a line refused before
    // it runs, as no message at all, quotes it (`unknown control message
    // "X"`).
    const failure = p.fs.failure[0..p.fs.failure_len];
    return tree.failText(req.tag, failureErrno(failure), std.fmt.bufPrint(&p.fs.ename, "{s}", .{failure}) catch failure);
}

const e_prompt = "control message needs its argument";

// ---- the root ctl ----

/// Every setting, one a line, in the words a write of it takes, so that the
/// file read back is the configuration, as webfs's ctl reads (webfs(4)).
/// What is not a setting -- platform, themes, where the config came from --
/// is /status's or the DumpConfig window's.
fn writeSettings(p: *Pardes, w: *std.Io.Writer) !void {
    try writeSettingsOf(p, &p.settings, w);
    try w.writeAll("LocationsConfig ");
    try p.locations_config.write(w);
    try w.writeByte('\n');
    if (comptime builtins.Pet.enabled) try w.print("Pet {s}\n", .{@tagName(p.settings.pet)});
}

/// The setting words of `s`, one a line, as the root ctl reads them; a Dump
/// keeps those that differ from a fresh session's (dump.zig).
pub fn writeSettingsOf(p: *Pardes, s: *const config.Runtime, w: *std.Io.Writer) !void {
    inline for (config.Runtime.settings) |setting| {
        if (comptime !setting.enabled(builtins.capabilities)) continue;
        const word = setting.word;
        switch (setting.action) {
            .toggle => |field| try w.print("{s} {s}\n", .{ word, if (@field(s, @tagName(field))) "on" else "off" }),
            .theme => if (s == &p.settings) {
                if (pardes.colors.loadedThemeFile(p)) |path| try w.print("ThemeFile {s}\n", .{path}) else try w.print("{s} {s}\n", .{ word, p.theme().name });
            } else try w.print("{s} {s}\n", .{ word, pardes.themes[s.theme].name }),
            .shell => {
                const chosen = s.shell.requested.get();
                try w.print("{s} {s}\n", .{ word, if (chosen.len > 0) chosen else config.defaultShell() });
            },
            .font => {
                const requested = s.font.requested_name.get();
                const name = if (requested.len > 0) requested else s.font.effective_name.get();
                const size = if (s.font.requested_size_hundredths != 0) s.font.requested_size_hundredths else s.font.effective_size_hundredths;
                if (name.len > 0 and size != 0)
                    try w.print("{s} {s}:{d}.{d:0>2}\n", .{ word, name, size / 100, size % 100 })
                else if (name.len > 0)
                    try w.print("{s} {s}\n", .{ word, name });
            },
            .tagline_size => try w.print("{s} {d}\n", .{ word, s.font.tagline_percent }),
            .window_opacity => try w.print("{s} {d}\n", .{ word, s.window_opacity }),
            .window_blur => try w.print("{s} {d}\n", .{ word, s.window_blur }),
            .choice => |which| switch (which) {
                inline else => |field| try w.print("{s} {s}\n", .{ word, @tagName(@field(s, @tagName(field))) }),
            },
            .message_ms => |which| try w.print("{s} {d}\n", .{ word, @field(s, "message_" ++ @tagName(which) ++ "_ms") }),
            // The directory in effect, as DumpConfig reports it; bare only when
            // there is none (no home to put the default in).
            .dump_dir => {
                var buf: [900]u8 = undefined;
                if (pardes.dump.directory(&buf, s.dump_dir.get())) |dir| try w.print("{s} {s}\n", .{ word, dir }) else try w.print("{s}\n", .{word});
            },
            .transition => |effect| try w.print("{s} {s}\n", .{ word, if (s.panel_transition == effect) "on" else "off" }),
            .scene => |effect| if (s.post.level(effect) == 0) try w.print("{s} off\n", .{word}) else try w.print("{s} {d}\n", .{ word, s.post.level(effect) }),
            .shader => for (s.post.list()) |entry| if (entry.scene == null) try w.print("{s} {s}\n", .{ word, entry.path.get() }),
            .shader_animation => try w.print("{s} {s}\n", .{ word, @tagName(s.shader_animation) }),
            .lift => try w.print("{s} {s}\n", .{ word, @tagName(s.lift) }),
            .motion => try w.print("{s} {s}\n", .{ word, @tagName(s.motion) }),
            .inactive_dim => try w.print("{s} {d}\n", .{ word, s.inactive_dim }),
            .grip_width => try w.print("{s} {d}\n", .{ word, s.grip_width }),
        }
    }
}

pub fn rootLen(p: *Pardes) u64 {
    var buf: [256]u8 = undefined;
    var counting: std.Io.Writer.Discarding = .init(&buf);
    writeSettings(p, &counting.writer) catch return 0;
    return counting.fullCount();
}

pub fn readRoot(p: *Pardes, req: Req) Reply {
    var text: std.Io.Writer.Allocating = .init(p.scratch.allocator());
    writeSettings(p, &text.writer) catch return Reply.fail(req.tag, E.NOMEM);
    p.fs.stage(p.gpa).appendSlice(p.gpa, text.written()) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

/// /pager, `pardes -`'s: the directory written (empty, or not absolute: the
/// session's) gets its one +Pager, made or emptied; the serial is what a
/// read of this same open answers, never another client's.
pub fn writePager(p: *Pardes, req: Req) Reply {
    // A refused write leaves its open no answer, not the last one's.
    p.fs.results_len = 0;
    var it = Messages.init(p, req.data);
    const line = it.next() orelse "";
    // Words 9ns maps back to EINVAL (`invalid`), as every refusal here.
    if (it.next() != null) return tree.failText(req.tag, E.INVAL, "pager: invalid write: one directory a write");
    // `~` is home, and `/tmp/../etc` is `/etc`: the +Pager is named in the
    // directory it is, as any other pane's name is.
    var home_buf: [4096]u8 = undefined;
    const typed = pardes.filesystem.expandHome(std.mem.trim(u8, line, " \t"), &home_buf);
    const dir = if (typed.len > 0 and typed[0] == '/') std.fs.path.resolvePosix(p.scratch.allocator(), &.{typed}) catch typed else typed;
    // A directory that is there, or none (the session's): never a +Pager
    // named into one missing, nor a relative one quietly taken for none.
    if (dir.len > 0 and dir[0] != '/') {
        var shown: [256]u8 = undefined;
        return tree.failText(req.tag, E.INVAL, std.fmt.bufPrint(&p.fs.ename, "pager: invalid directory \"{s}\": must be absolute", .{blanked(dir[0..@min(dir.len, shown.len)], &shown)}) catch "pager: invalid directory: must be absolute");
    }
    if (comptime pardes.hosted) if (dir.len > 0) if (pardes.filesystem.localPath(dir)) |local| if (!exec_line.isDirectory(local))
        return tree.failText(req.tag, E.NOENT, std.fmt.bufPrint(&p.fs.ename, "pager: {s}: no such directory", .{dir[0..@min(dir.len, 256)]}) catch "pager: no such directory");
    // Nor one that may not be written, as a file's name there is refused.
    if (comptime pardes.hosted) if (dir.len > 0) if (pardes.filesystem.localPath(dir)) |local| if (pardes.filesystem.deniedAbove(local))
        return tree.failText(req.tag, E.PERM, std.fmt.bufPrint(&p.fs.ename, "pager: {s}: permission denied", .{dir[0..@min(dir.len, 256)]}) catch "pager: permission denied");
    const id = pardes.panes.Output.openPager(p, p.active, dir) catch |err|
        return tree.failText(req.tag, if (err == error.NoPaneRoom or err == error.NoPaneSlots) E.NOSPC else E.IO, switch (err) {
            error.NoPaneRoom, error.NoPaneSlots => "pager: no space for a +Pager pane",
            else => "pager: could not make a +Pager pane",
        });
    noteResult(p, p.panes[id].?.serial);
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

/// One session builtin a line, at whichever pane has the keyboard as each
/// runs, as the root's look and exec click there; all are checked first.
pub fn writeRoot(p: *Pardes, req: Req) Reply {
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var it = Messages.init(p, req.data);
        while (it.next()) |line| {
            if (line.len == 0 or exec_line.isComment(line)) continue;
            if (std.mem.startsWith(u8, line, "size ") or std.mem.eql(u8, line, "size")) {
                // The offending word is the value: `size 5 5` quotes "5 5".
                const value = std.mem.trim(u8, line["size".len..], " \t");
                const size = sizeOf(line) orelse return refuseQuoting(p, req, e_size, value);
                // A frontend's window is the size; only a session none is
                // attached to (--detach, unattended) takes one written.
                if (!p.unattended) return refuseQuoting(p, req, "size: a frontend is attached and owns the size", value);
                if (apply) {
                    const was: [2]u16 = .{ p.screen_w, p.screen_h };
                    const before = p.rects;
                    p.update(.{ .resize = .{ .cols = size[0], .rows = size[1] } });
                    p.sync();
                    // Every pane keeps its tag and two rows, as placement
                    // leaves them (layout.minRows, the one minimum): a size
                    // too small for the panes' minima is refused, and one
                    // they fit gives back rows the resize took under them.
                    if (!pardes.layout.minimaFit(p)) {
                        p.update(.{ .resize = .{ .cols = was[0], .rows = was[1] } });
                        p.sync();
                        return refuseQuoting(p, req, "size: too small for the panes, each its tag and 2 rows", value);
                    }
                    pardes.layout.restoreMinima(p, &before);
                    p.sync();
                }
                continue;
            }
            if (!apply) {
                if (checkBuiltin(p, req, line, .session)) |refusal| return refusal;
                continue;
            }
            // An empty window (no pane at all) still takes its session words.
            if (p.panes[p.active] == null and p.anyPane() != null) return Reply.fail(req.tag, E.NOENT);
            p.fs.session_write = true;
            defer p.fs.session_write = false;
            if (runBuiltin(p, req, p.active, line)) |refusal| return refusal;
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

const size_min = [2]u16{ 20, 6 };
const size_max = [2]u16{ 4096, 4096 };
// "invalid": the word 9ns reads as EINVAL (enameToErrno), as winsize's.
const e_size = std.fmt.comptimePrint("invalid size: takes <cols> <rows>, at least {d}x{d}, at most {d}x{d}", .{ size_min[0], size_min[1], size_max[0], size_max[1] });

/// `size <cols> <rows>`, within size_min and size_max.
fn sizeOf(line: []const u8) ?[2]u16 {
    var it = std.mem.tokenizeAny(u8, line["size".len..], " \t");
    const cols = std.fmt.parseInt(u16, it.next() orelse return null, 10) catch return null;
    const rows = std.fmt.parseInt(u16, it.next() orelse return null, 10) catch return null;
    if (it.next() != null or cols < size_min[0] or rows < size_min[1] or cols > size_max[0] or rows > size_max[1]) return null;
    return .{ cols, rows };
}

// ---- /commands ----

/// Every builtin the registry holds, one a line: its word, `arg` when it
/// takes one, and which ctl takes it, `root` or `pane` -- the registry
/// itself, so a new builtin is listed the moment it exists.
/// A builtin's doc comment, its first sentence, from the source itself: a
/// line of /commands says what each word does without a second copy of it.
fn summaryOf(word: []const u8, buf: []u8) []const u8 {
    const source = @embedFile("../builtins.zig");
    var needle_buf: [64]u8 = undefined;
    const needle = std.fmt.bufPrint(&needle_buf, "\npub const {s} = struct", .{word}) catch return "";
    const at = std.mem.indexOf(u8, source, needle) orelse return "";
    // Back over the `///` lines just above it.
    var start = at + 1;
    while (start > 0) {
        const prev_end = start - 1;
        const prev_start = if (std.mem.lastIndexOfScalar(u8, source[0..prev_end], '\n')) |nl| nl + 1 else 0;
        if (!std.mem.startsWith(u8, std.mem.trimStart(u8, source[prev_start..prev_end], " "), "///")) break;
        start = prev_start;
    }
    var w = std.Io.Writer.fixed(buf);
    var lines = std.mem.splitScalar(u8, source[start .. at + 1], '\n');
    while (lines.next()) |line| {
        const text = std.mem.trim(u8, std.mem.trimStart(u8, std.mem.trimStart(u8, line, " "), "/"), " ");
        if (text.len == 0) continue;
        if (w.buffered().len > 0) w.writeByte(' ') catch break;
        w.writeAll(text) catch break;
    }
    const all = stripCitations(w.buffered());
    // The first sentence, whole: to a `.` that ends one.
    var i: usize = 0;
    while (std.mem.indexOfScalarPos(u8, all, i, '.')) |dot| : (i = dot + 1) {
        if (dot + 1 == all.len or all[dot + 1] == ' ') return all[0 .. dot + 1];
    }
    return all;
}

/// Drops a parenthesis that cites source (`(editors/acme/exec.c:892)`,
/// `(exec.c, \`kill\`; acme.c's WKill)`): a reader of /commands wants what
/// the word does, not where acme has it. In place; answers the rest.
fn stripCitations(text: []u8) []u8 {
    var out: usize = 0;
    var i: usize = 0;
    while (i < text.len) {
        if (text[i] == '(') if (std.mem.indexOfScalarPos(u8, text, i, ')')) |close| {
            const inside = text[i + 1 .. close];
            if (std.mem.indexOf(u8, inside, ".c") != null or std.mem.indexOf(u8, inside, ".zig") != null) {
                // With the space before it, and a colon after it kept.
                if (out > 0 and text[out - 1] == ' ') out -= 1;
                i = close + 1;
                continue;
            }
        };
        text[out] = text[i];
        out += 1;
        i += 1;
    }
    return text[0..out];
}

fn writeCommands(w: *std.Io.Writer) !void {
    for (std.enums.values(Builtin)) |b| {
        // Edit is a pane's word the root's ctl takes too, at the active pane.
        const scope: []const u8 = if (b == .Edit) "both" else if (builtins.registry.scope(b) == .session) "root" else "pane";
        try w.print("{s}{s} {s}", .{
            @tagName(b),
            if (builtins.registry.takesArg(b)) " arg" else "",
            scope,
        });
        // A setting that chooses among words: the words, comma-joined. Bare,
        // it steps to the next of them (a two-valued one flips).
        if (config.Runtime.find(@tagName(b))) |setting| if (config.Runtime.choices(setting.action)) |values| {
            try w.writeByte(' ');
            var parts = std.mem.splitSequence(u8, values, ", ");
            var first = true;
            while (parts.next()) |v| : (first = false) try w.print("{s}{s}", .{ if (first) "" else ",", v });
        };
        // Then ` -- ` and what it does: a setting's doc, else its source's.
        var summary_buf: [2048]u8 = undefined;
        const summary = if (config.Runtime.find(@tagName(b))) |setting| setting.doc else summaryOf(@tagName(b), &summary_buf);
        if (summary.len > 0) {
            // The sentence whole unless it is long, then cut between words.
            const kept = @import("../Messages.zig").clip(summary, 240);
            try w.print(" -- {s}{s}", .{ kept, if (kept.len < summary.len) "…" else "" });
        }
        try w.writeByte('\n');
    }
}

pub fn commandsLen() u64 {
    var buf: [256]u8 = undefined;
    var counting: std.Io.Writer.Discarding = .init(&buf);
    writeCommands(&counting.writer) catch return 0;
    return counting.fullCount();
}

pub fn readCommands(p: *Pardes, req: Req) Reply {
    var text: std.Io.Writer.Allocating = .init(p.scratch.allocator());
    writeCommands(&text.writer) catch return Reply.fail(req.tag, E.NOMEM);
    p.fs.stage(p.gpa).appendSlice(p.gpa, text.written()) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

// ---- /focus ----

/// The pane with the keyboard, which a write of a serial moves, the way
/// writing `current` to rio's wctl does (rio(4)). While a column's or the
/// workspace's tag has it, no pane does, and this reads empty. A write
/// gives the keyboard and nothing else: a folded pane stays folded, as
/// rio keeps `current` apart from `unhide`.
pub fn readFocus(p: *Pardes, req: Req) Reply {
    const out = p.fs.stage(p.gpa);
    if (p.header_focus) return tree.stagedReply(p, req);
    const pane = p.panes[p.active] orelse return tree.stagedReply(p, req);
    out.print(p.gpa, "{d}\n", .{pane.serial}) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

pub fn writeFocus(p: *Pardes, req: Req) Reply {
    const text = std.mem.trim(u8, req.data, " \t\r\n");
    const serial = std.fmt.parseInt(u32, text, 10) catch return tree.failText(req.tag, E.INVAL, tree.e_bad_ctl);
    const id = p.paneBySerial(serial) orelse return tree.failText(req.tag, E.NOENT, e_no_pane);
    // The keyboard goes to the pane itself, off any header that had it, and
    // its column becomes the active one, as the user's click there would
    // make it: pane/new and a look place there next, whatever Placement.
    tagline.exitHeader(p);
    p.active = id;
    if (pardes.layout.findPane(p, id)) |at| p.setActiveColumn(at.col);
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

const e_no_pane = "no such pane";

pub fn readPane(p: *Pardes, req: Req, pane: *Pane) Reply {
    var buf: [pane_text_cap]u8 = undefined;
    const out = p.fs.stage(p.gpa);
    out.appendSlice(p.gpa, paneText(p, pane, &buf)) catch return Reply.fail(req.tag, E.NOMEM);
    return tree.stagedReply(p, req);
}

/// `get` reloads the buffer from the name it carries, wherever that name
/// resolves. Any other line is a builtin that acts on a pane (`Del`,
/// `Save f`), run at this one; a session's builtin is the root ctl's.
///
/// `lock` and `unlock` are acme's (editors/acme/xfid.c:603-611), so that a
/// client can make an edit of several writes to addr and data without
/// another's landing in between. As in acme the lock binds only the clients
/// that ask for it; a write to any other file is never refused for it, nor
/// is the person at the keyboard. It belongs to the open that wrote it,
/// which alone may `unlock`, and closing that open or the pane gives it up.
/// Where acme's qlock blocks a second locker, this refuses it at once with
/// `file in use`, and the client tries again: through a kernel or FUSE
/// mount a blocked write holds the file's writes, the holder's own `unlock`
/// and close among them, so a waiting lock would never be let in.
pub fn writePane(p: *Pardes, req: Req, pane: *Pane) Reply {
    // This open's handle is what holds the lock; a write that came on no
    // writable open (the editor's own) has none.
    const mine: ?u32 = if (tree.openOf(p, req)) |o| (if (o.what == .ctl) req.handle else null) else null;
    // The pane keeps the holder's handle, which names that open only on
    // this pane's ctl node; one that no longer does holds nothing.
    if (pane.fs.lock) |h| {
        const o = tree.openOf(p, .{ .tag = 0, .op = .write, .node = tree.Node.of(pane.serial, .ctl), .handle = h });
        if (o == null or o.?.what != .ctl) pane.fs.lock = null;
    }
    const other = pane.fs.lock != null and pane.fs.lock != mine;
    const serial = pane.serial;
    // Checked whole before anything applies, so a write that must wait for
    // the lock has done nothing yet when it goes again.
    for ([2]bool{ false, true }) |apply| {
        if (apply) p.fs.results_len = 0;
        var held = !other and pane.fs.lock != null;
        var it = Messages.init(p, req.data);
        while (it.next()) |line_in| {
            if (line_in.len == 0 or exec_line.isComment(line_in)) continue;
            // A line before this one may have closed the pane (`Del`).
            if (apply and p.paneBySerial(serial) == null) return Reply.fail(req.tag, E.NOENT);
            // acme's ctl words: done by the file that replaces each, or the
            // builtin that does it, checked with the rest before any runs.
            var line = line_in;
            switch (acmeCtl(p, req, serial, line_in, apply)) {
                .no => {},
                .done => continue,
                .refused => |r| return r,
                .builtin => |word| line = word,
            }
            if (std.mem.eql(u8, line, "get")) {
                if (!apply) continue;
                // Quoting the line, as a builtin's refusal (Save's) does.
                if (getRefused(p, pane)) |said_in_ename| {
                    // refuse writes ename, where the words are: copy them out.
                    var said_buf: [320]u8 = undefined;
                    const said = said_buf[0..said_in_ename.len];
                    @memcpy(said, said_in_ename);
                    // It ran and was refused: its words, not the line quoted.
                    return tree.failText(req.tag, E.IO, std.fmt.bufPrint(&p.fs.ename, "{s}", .{said}) catch said);
                }
                var failed: anyerror = error.Unexpected;
                const errno = get(p, pane, &failed);
                // Naming the path, in words 9ns reads as the errno; a peer
                // out of reach as a look or a Save says it.
                if (errno != 0) {
                    const path = if (pane_files.fileOf(pane)) |f| f.path else "";
                    var why_buf: [48]u8 = undefined;
                    const why = if (pardes.Messages.dialReason(failed)) |r|
                        std.fmt.bufPrint(&why_buf, "dial failed: {s}", .{r}) catch "dial failed"
                    else if (errno == E.NOENT) "no such file" else "cannot be read";
                    return tree.failText(req.tag, errno, std.fmt.bufPrint(&p.fs.ename, "get: {s}: {s}", .{ path[0..@min(path.len, 256)], why }) catch "get: no such file");
                }
            } else if (std.mem.eql(u8, line, "lock")) {
                if (mine == null) return tree.failText(req.tag, E.INVAL, tree.e_bad_ctl);
                if (other) return tree.failText(req.tag, E.BUSY, e_locked);
                held = true;
                if (apply) pane.fs.lock = mine;
            } else if (std.mem.eql(u8, line, "unlock")) {
                if (!held) return tree.failText(req.tag, E.INVAL, e_not_locked);
                held = false;
                if (apply) pane.fs.lock = null;
            } else if (std.mem.eql(u8, line, "answer")) {
                // With a question up, what it offers.
                var offered: [64]u8 = undefined;
                if (p.questionChoices(p.paneBySerial(serial).?, &offered)) |choices| {
                    var why: [96]u8 = undefined;
                    return tree.failText(req.tag, E.INVAL, std.fmt.bufPrint(&p.fs.ename, "answer takes {s} or -", .{choices}) catch std.fmt.bufPrint(&why, "answer takes a choice or -", .{}) catch "answer takes a choice or -");
                }
                return tree.failText(req.tag, E.INVAL, "answer takes a choice or -");
            } else if (std.mem.startsWith(u8, line, "answer ") and p.panes[p.paneBySerial(serial).?].?.prompt == .save) {
                // Save's path, asked over 9P (`ask <serial> save path`).
                if (!apply) continue;
                const id = p.paneBySerial(serial).?;
                const asked = p.panes[id].?;
                const path = std.mem.trim(u8, line["answer ".len..], " ");
                var rec: [300]u8 = undefined;
                pardes.ctlfs.events.notePath(p, "answer", std.fmt.bufPrint(&rec, "{d} {s}", .{ serial, path[0..@min(path.len, 256)] }) catch "");
                if (!std.mem.eql(u8, path, "-")) exec_line.saveTo(p, id, path);
                asked.closePrompt();
            } else if (std.mem.startsWith(u8, line, "answer ")) {
                // The pane's question (its `ask` in the log), answered.
                const choice = std.mem.trim(u8, line["answer ".len..], " ");
                const id = p.paneBySerial(serial).?;
                var offered: [64]u8 = undefined;
                const choices = p.questionChoices(id, &offered) orelse return refuse(p, req, "no question asked", line);
                // Only a choice the question offers answers it; anything
                // else leaves it standing, and says what it takes.
                if (!std.mem.eql(u8, choice, "-") and (choice.len != 1 or std.mem.indexOfScalar(u8, choices, choice[0]) == null)) {
                    var why: [96]u8 = undefined;
                    return refuse(p, req, std.fmt.bufPrint(&why, "answer takes {s} or -", .{choices}) catch "answer takes a choice or -", line);
                }
                if (apply) _ = p.answerQuestion(id, if (choice[0] == '-') null else choice[0]);
            } else if (!apply) {
                if (checkBuiltin(p, req, line, .pane)) |refusal| return refusal;
                // Edit on a pane with no text is the refusal a data write
                // there gets, EINVAL, before anything runs.
                if (std.mem.startsWith(u8, line, "Edit") and pane_files.fileOf(p.panes[p.paneBySerial(serial).?].?) == null)
                    return tree.failText(req.tag, E.INVAL, pane_files.e_no_text);
            } else if (runBuiltin(p, req, p.paneBySerial(serial).?, line)) |refusal| {
                return refusal;
            }
        }
    }
    return .{ .tag = req.tag, .written = @intCast(req.data.len) };
}

/// acme's pane ctl vocabulary (editors/acme/xfid.c xfidctlwrite): each word
/// done here by the file that replaces it, or run as the builtin that does
/// it; those with no place here refused with why.
const AcmeCtl = union(enum) { no, done, refused: Reply, builtin: []const u8 };

fn acmeCtl(p: *Pardes, req: Req, serial: u32, line: []const u8, apply: bool) AcmeCtl {
    const id = p.paneBySerial(serial) orelse return .no;
    const pane = p.panes[id].?;
    const word = line[0 .. std.mem.indexOfScalar(u8, line, ' ') orelse line.len];
    const rest = std.mem.trim(u8, line[word.len..], " ");
    const File = tree.PaneFile;
    // A word written to one of the pane's own files, as acme's is to its.
    const Into = struct { file: File, data: []const u8 };
    // `name` takes all after its one blank, as the name file takes what is
    // written. A second blank after the word is refused, not taken as the
    // name's first byte: a line's words are split at blanks.
    if (std.mem.eql(u8, word, "name") and rest.len > 0 and line[word.len + 1] == ' ')
        return .{ .refused = tree.failText(req.tag, E.INVAL, "bad character in file name: a blank at its start") };
    const into: ?Into = if (std.mem.eql(u8, word, "name") and rest.len > 0)
        .{ .file = .name, .data = line[word.len + 1 ..] }
    else if (std.mem.eql(u8, line, "clean"))
        .{ .file = .dirty, .data = "0" }
    else if (std.mem.eql(u8, line, "dirty"))
        .{ .file = .dirty, .data = "1" }
    else if (std.mem.eql(u8, line, "mark"))
        .{ .file = .mark, .data = "1" }
    else if (std.mem.eql(u8, line, "nomark"))
        .{ .file = .mark, .data = "0" }
    else
        null;
    if (into) |w| {
        if (!apply) return .done;
        const r = pane_files.write(p, .{ .tag = req.tag, .op = .write, .node = tree.Node.of(serial, w.file), .data = w.data }, id, pane, w.file);
        return if (r.status == .err) .{ .refused = r } else .done;
    }
    if (std.mem.eql(u8, line, "put")) return .{ .builtin = "Save" };
    if (std.mem.eql(u8, line, "del")) return .{ .builtin = "Del" };
    if (std.mem.eql(u8, line, "delete")) return .{ .builtin = "Delete" };
    const pf = &pane.fs;
    if (std.mem.eql(u8, line, "dot=addr")) {
        if (apply) pane_files.setDot(pane, pf.addr);
        return .done;
    }
    if (std.mem.eql(u8, line, "addr=dot")) {
        if (apply) pf.addr = pane_files.dotOf(pane);
        return .done;
    }
    if (std.mem.eql(u8, line, "limit=addr")) {
        if (apply) pf.limit = pf.addr;
        return .done;
    }
    if (std.mem.eql(u8, line, "show")) {
        if (apply) pane_files.showOffset(pane, pane_files.dotOf(pane).q0);
        return .done;
    }
    if (std.mem.eql(u8, line, "cleartag")) {
        if (apply) _ = pane_files.truncate(p, pane, .tag);
        return .done;
    }
    const none: ?[]const u8 = if (std.mem.eql(u8, word, "dump") or std.mem.eql(u8, word, "dumpdir"))
        "a pane is dumped with the session: Dump and DumpDir on /ctl"
    else if (std.mem.eql(u8, word, "font"))
        "the font is the session's: Font on /ctl"
    else if (std.mem.eql(u8, line, "menu") or std.mem.eql(u8, line, "nomenu"))
        "pardes has no menu"
    else
        null;
    if (none) |why| return .{ .refused = tree.failText(req.tag, E.INVAL, std.fmt.bufPrint(&p.fs.ename, "invalid: acme's {s}: {s}", .{ word, why }) catch "invalid: acme's ctl word") };
    return .no;
}

const e_not_locked = "pane not locked by this open";
/// Who holds it is another open of this ctl, whose client pardes cannot name.
const e_locked = tree.e_in_use ++ ": another open of this ctl holds the lock";

/// acme's get asks winclean first (exec.c:513): unsaved text is warned
/// about once, and the same get again, nothing edited since, discards it.
fn getRefused(p: *Pardes, pane: *Pane) ?[]const u8 {
    const f = pane_files.fileOf(pane) orelse return null;
    if (!panes.Output.fileTraits(f.output).saves or f.revision == f.saved_revision) return null;
    // Dirty by a rename alone is no text to lose: only edits are asked about.
    const saved = f.saved_hash orelse return null;
    if (std.hash.Wyhash.hash(0, f.content) == saved) return null;
    if (pane.discard_warned) |w| if (w.revision == f.revision and w.by == .get) return null;
    pane.discard_warned = .{ .revision = f.revision, .by = .get };
    const id = p.paneBySerial(pane.serial).?;
    // Kept in +Unsaved, as Exit's refusal is; the notice is short. The
    // write's err record logs it, not a msg too.
    // And logged `unsaved <serial> <name>`, as the other refusals are.
    tree.events.noteLog(p, .unsaved, pane);
    const listed = std.fmt.allocPrint(p.gpa, "{s}: Modified\n\nget again to discard\n", .{f.path}) catch null;
    if (listed) |content| panes.Output.openUnsaved(p, id, content);
    p.fs.unlogged = true;
    p.setMessage(id, "1 unsaved pane \u{2014} get again to discard");
    p.fs.unlogged = false;
    return std.fmt.bufPrint(&p.fs.ename, "{s}: Modified (get again to discard)", .{f.path}) catch "Modified (get again to discard)";
}

fn get(p: *Pardes, pane: *Pane, failed: *anyerror) u16 {
    const f = pane_files.fileOf(pane) orelse return 0;
    if (!panes.Output.fileTraits(f.output).saves) return 0;
    const bytes = fs.read(p, f.path) catch |err| {
        failed.* = err;
        return switch (err) {
            error.FileNotFound => E.NOENT,
            else => E.IO,
        };
    };
    // Throwing unsaved edits away for it is a reload the log hears of, as a
    // clean one from the watch is.
    const discarded = f.revision != f.saved_revision;
    panes.File.pushUndo(p, pane);
    panes.File.setContent(p, f, bytes);
    f.saved_revision = f.revision;
    f.saved_hash = std.hash.Wyhash.hash(0, f.content);
    f.saved_len = f.content.len;
    f.disk_newer = null;
    f.disk_gone = false;
    if (discarded) {
        var rec: [32]u8 = undefined;
        pardes.ctlfs.events.notePath(p, "changed", std.fmt.bufPrint(&rec, "{d} reloaded", .{pane.serial}) catch "");
    }
    return 0;
}

// ---- tests ----

const testing = std.testing;
const th = @import("testing.zig");
const call = th.call;
const rd = th.rd;
const wr = th.wr;
const withFile = th.withFile;
const serialOf = th.serialOf;
const Node = tree.Node;
const Status = tree.Status;
const root_status = @intFromEnum(tree.TopFile.status);
const root_look = @intFromEnum(tree.TopFile.look);
const root_exec = @intFromEnum(tree.TopFile.exec);

test "a control character in a write to any ctl refuses the whole write, and a quoted line shows a tab as a blank" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const col = layout.columnSerial(p, 0);
    for ([_]u64{ @intFromEnum(tree.TopFile.ctl), Node.of(serialOf(p), .ctl), Node.ofCol(col, .ctl) }) |node| {
        const r = wr(p, node, "Wrap off\nbo\x01gus\n");
        try testing.expectEqual(E.INVAL, r.errno());
        try testing.expectEqualStrings(e_control, r.reply.ename);
    }
    const quoted = wr(p, Node.of(serialOf(p), .ctl), "bogus\tword\n");
    try testing.expectEqual(E.INVAL, quoted.errno());
    // The offending word alone is quoted: a tab ends it.
    try testing.expect(std.mem.indexOf(u8, quoted.reply.ename, "\"bogus\"") != null);
    try testing.expect(std.mem.indexOfScalar(u8, quoted.reply.ename, '\t') == null);
}

test "pane ctl read is acme's fields -- index's five, width in cells, font, tab width, undo, redo -- then whether it is current" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const pane = p.panes[0].?;

    const a = rd(p, Node.of(pane.serial, .ctl), 0, 4096);
    try testing.expectEqual(Status.ok, a.reply.status);
    var want: std.ArrayList(u8) = .empty;
    defer want.deinit(gpa);
    try want.print(gpa, "{d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {d:>11} {s} {d:>11} {d:>11} {d:>11} current ", .{
        pane.serial, pane_files.tagOf(p, pane).len, @as(usize, 2), 0, 0, pane.cols, "default", config.tab_width, 0, 0,
    });
    try testing.expectEqualStrings(want.items, a.bytes);
    try testing.expectEqual(@as(u64, a.bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = Node.of(pane.serial, .ctl) }).reply.attr.size);

    var quoted: [64]u8 = undefined;
    var w = std.Io.Writer.fixed(&quoted);
    try writeQuoted(&w, "DejaVu Sans Mono");
    try testing.expectEqualStrings("'DejaVu Sans Mono'", w.buffered());
    w = std.Io.Writer.fixed(&quoted);
    try writeQuoted(&w, "it's");
    try testing.expectEqualStrings("'it''s'", w.buffered());
}

test "commands lists every builtin with its argument and the ctl that takes it" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const node = @intFromEnum(tree.TopFile.commands);
    const listed = rd(p, node, 0, 1 << 16);
    try testing.expectEqual(@as(u64, listed.bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = node }).reply.attr.size);
    try testing.expectEqual(E.PERM, wr(p, node, "Del\n").errno());
    var lines: usize = 0;
    var it = std.mem.tokenizeScalar(u8, listed.bytes, '\n');
    while (it.next()) |line| : (lines += 1) {
        var words = std.mem.tokenizeScalar(u8, line, ' ');
        const b = std.meta.stringToEnum(Builtin, words.next().?).?;
        if (builtins.registry.takesArg(b)) try testing.expectEqualStrings("arg", words.next().?);
        try testing.expectEqualStrings(if (b == .Edit) "both" else if (builtins.registry.scope(b) == .session) "root" else "pane", words.next().?);
        if (config.Runtime.find(@tagName(b))) |s| if (config.Runtime.choices(s.action) != null) try testing.expect(words.next() != null);
        // Then, where the source has one, ` -- ` and what it does.
        if (words.next()) |dashes| try testing.expectEqualStrings("--", dashes);
    }
    try testing.expectEqual(std.enums.values(Builtin).len, lines);
    for ([_][]const u8{ "\nDel arg pane -- ", "\nNewcol root -- ", "\nSave arg pane", "\nVerbose arg root on,off", "\nPlacement arg root acme,pardes", "\nUndo pane -- ", "\nEdit arg both -- acme's Edit" }) |row|
        try testing.expect(std.mem.indexOf(u8, listed.bytes, row) != null);
}

test "Undo and Redo on a pane's ctl step its body through its edits" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, body, "two\n").reply.status);
    try testing.expectEqualStrings("one\ntwo\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expectEqualStrings("one\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expectEqualStrings("one\ntwo\n", rd(p, body, 0, 64).bytes);
    // Nothing left: said, and the write still succeeds, as acme's is silent.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expect(th.logHas(p, "Redo: nothing to redo"));
    _ = wr(p, Node.of(serial, .ctl), "Undo");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expect(th.logHas(p, "Undo: nothing to undo"));
    // Said again word for word, it is that line counted, as err's are.
    for (0..3) |_| _ = wr(p, Node.of(serial, .ctl), "Undo");
    try testing.expect(th.logHas(p, "Undo: nothing to undo (x4)\n"));
}

test "focus reads the pane with the keyboard, and a serial written to it moves the keyboard there" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const first = serialOf(p);
    const second = try th.newPane(p);
    const focus = @intFromEnum(tree.TopFile.focus);
    var line: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&line, "{d}\n", .{second}), rd(p, focus, 0, 64).bytes);
    try testing.expectEqual(@as(u64, rd(p, focus, 0, 64).bytes.len), call(p, .{ .tag = 1, .op = .getattr, .node = focus }).reply.attr.size);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(first, .ctl), 0, 4096).bytes, " notcurrent "));

    // A header has the keyboard: no pane does, and a write takes it back.
    tagline.enterHeader(p, null);
    try testing.expectEqualStrings("", rd(p, focus, 0, 64).bytes);
    try testing.expectEqual(@as(u64, 0), call(p, .{ .tag = 1, .op = .getattr, .node = focus }).reply.attr.size);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(second, .ctl), 0, 4096).bytes, " notcurrent "));
    try testing.expectEqual(Status.ok, wr(p, focus, try std.fmt.bufPrint(&line, "{d}\n", .{first})).reply.status);
    try testing.expect(!p.header_focus);
    try testing.expectEqual(p.paneBySerial(first).?, p.active);
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(first, .ctl), 0, 4096).bytes, " current "));
    try testing.expect(std.mem.endsWith(u8, rd(p, Node.of(second, .ctl), 0, 4096).bytes, " notcurrent "));

    try testing.expectEqualStrings(e_no_pane, wr(p, focus, "99999\n").reply.ename);
    try testing.expectEqual(E.NOENT, wr(p, focus, "99999").errno());
    for ([_][]const u8{ "", "two", "-1", "1 2" }) |bad| try testing.expectEqual(E.INVAL, wr(p, focus, bad).errno());
    try testing.expectEqual(p.paneBySerial(first).?, p.active);

    // Focus gives the keyboard only: a folded pane stays folded.
    const folded = p.paneBySerial(second).?;
    layout.toggleCollapse(p, folded);
    try testing.expect(p.panes[folded].?.collapsed);
    try testing.expectEqual(Status.ok, wr(p, focus, try std.fmt.bufPrint(&line, "{d}", .{second})).reply.status);
    try testing.expectEqual(folded, p.active);
    try testing.expect(p.panes[folded].?.collapsed);
}

test "the pane ctl takes acme's verbs and the pane's builtins, and refuses the rest in Plan 9's words" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    // A builtin is its own capitalised word: `GET` and `DEL` are none;
    // acme's own words are done or refused as acme's (the test below).
    for ([_][]const u8{ "lock x", "bogus", "DEL", "GET", "get x", "look /tmp", "exec Del" }) |bad| {
        const refused = wr(p, ctl_node, bad);
        try testing.expectEqual(E.INVAL, refused.errno());
        var want: [64]u8 = undefined;
        try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "unknown control message \"{s}\"", .{firstWord(bad)}), refused.reply.ename);
    }
    try testing.expectEqualStrings("not a window control message \"Newcol\": write it to /ctl", wr(p, ctl_node, "Newcol").reply.ename);
    try testing.expectEqualStrings("not a window control message \"Verbose\": write it to /ctl", wr(p, ctl_node, "Verbose off").reply.ename);
    try testing.expectEqualStrings("wrong #args in control message \"Collapse\"", wr(p, ctl_node, "Collapse now").reply.ename);
    // Checked whole first: a bad line anywhere and nothing ran.
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "Msg first\nbogus").errno());
    try testing.expect(p.panes[0].?.msg_len == 0 or !std.mem.eql(u8, p.panes[0].?.msg[0..p.panes[0].?.msg_len], "first"));

    // A pane's builtin runs at that pane.
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Msg from ctl\n").reply.status);
    const pane = p.panes[p.paneBySerial(serial).?].?;
    try testing.expectEqualStrings("from ctl", pane.msg[0..pane.msg_len]);
    // One that means nothing bare is refused before anything runs.
    try testing.expectEqualStrings("wrong #args in control message \"Find\"", wr(p, ctl_node, "Find").reply.ename);
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "Msg first\nMsg").errno());
    try testing.expect(!std.mem.eql(u8, pane.msg[0..pane.msg_len], "first"));
    try testing.expect(pane.prompt == .none);
    try testing.expect(!p.fs.no_prompt);
    // Save with no name on a scratch would ask for one: refused, not asked.
    const other = try th.newPane(p);
    try testing.expectEqualStrings(e_prompt ++ " \"Save\"", wr(p, Node.of(other, .ctl), "Save").reply.ename);
    try testing.expect(p.panes[p.paneBySerial(other).?].?.prompt == .none);
    // A line after the one that closed the pane has nowhere to run.
    try testing.expectEqual(E.NOENT, wr(p, Node.of(other, .ctl), "Del\nMsg after").errno());
    try testing.expect(p.paneBySerial(other) == null);
}

test "the root ctl reads the settings as a write takes them, and takes the session's builtins" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const first = rd(p, root_ctl, 0, 1 << 16);
    try testing.expectEqual(Status.ok, first.reply.status);
    const settings = try gpa.dupe(u8, first.bytes);
    defer gpa.free(settings);
    try testing.expectEqual(@as(u64, settings.len), call(p, .{ .tag = 1, .op = .getattr, .node = root_ctl }).reply.attr.size);
    try testing.expect(std.mem.indexOf(u8, settings, "Verbose on\n") != null);
    try testing.expect(std.mem.indexOf(u8, settings, "LocationsConfig ") != null);
    // Settings only: nothing /status or the DumpConfig window says.
    try testing.expect(std.mem.indexOf(u8, settings, "Platform") == null);
    try testing.expect(std.mem.indexOf(u8, settings, "requested") == null);

    // Every line written back is taken, and changes nothing.
    try testing.expectEqual(Status.ok, wr(p, root_ctl, settings).reply.status);
    try testing.expectEqualStrings(settings, rd(p, root_ctl, 0, 1 << 16).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Verbose off\n").reply.status);
    try testing.expect(!p.settings.verbose);
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "Verbose off\n") != null);
    const columns = p.ncol;
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Newcol\n").reply.status);
    try testing.expectEqual(columns + 1, p.ncol);

    try testing.expectEqualStrings("not a session control message \"Del\": write it to pane/<n>/ctl", wr(p, root_ctl, "Del").reply.ename);
    try testing.expectEqualStrings("unknown control message \"Nonsense\"", wr(p, root_ctl, "Nonsense 1").reply.ename);
    try testing.expectEqualStrings("bad value in control message; takes on, off \"maybe\"", wr(p, root_ctl, "Verbose maybe").reply.ename);
    try testing.expectEqualStrings("bad value in control message; takes acme, pardes \"east\"", wr(p, root_ctl, "Placement east").reply.ename);
    // A number's refusal names its range, a path's what it takes.
    try testing.expectEqualStrings("bad value in control message; takes 0-100 (a percentage) \"200\"", wr(p, root_ctl, "InactiveDim 200").reply.ename);
    try testing.expectEqualStrings("bad value in control message; takes 0-60000 (milliseconds) \"x\"", wr(p, root_ctl, "MessageLinger x").reply.ename);
    for (config.Runtime.settings) |setting| if (setting.action != .theme)
        try testing.expect(config.Runtime.takes(setting.action) != null);
    const no_theme = wr(p, root_ctl, "Theme no-such-theme").reply.ename;
    try testing.expectStringStartsWith(no_theme, "bad value in control message; like it: n");
    try testing.expect(std.mem.endsWith(u8, no_theme, "; Themes lists all \"no-such-theme\""));
    try testing.expectEqualStrings("wrong #args in control message \"Newcol\"", wr(p, root_ctl, "Newcol 2").reply.ename);
    try testing.expectEqualStrings("wrong #args in control message \"Theme\"", wr(p, root_ctl, "Theme").reply.ename);
    // A bare required word fails the check, so the line before never runs.
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "Verbose on\nMount").errno());
    try testing.expect(!p.settings.verbose);
    // A builtin that fails as it runs fails the write, quoting its error and
    // its line; the lines before it have taken effect, as in acme.
    const failed = wr(p, root_ctl, "Verbose on\nMount x /tmp/pardes-no-such-sock-zz\nVerbose off");
    try testing.expectEqual(E.IO, failed.errno());
    try testing.expectStringStartsWith(failed.reply.ename, "Mount x /tmp/pardes-no-such-sock-zz: dial failed");
    try testing.expect(p.settings.verbose);
    try testing.expect(!p.fs.no_prompt);
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Verbose off").reply.status);
}


test "a second lock is refused until the holder unlocks or closes, and binds nobody else" {
    const p = try withFile(testing.allocator, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const w = struct {
        fn ctl(pp: *Pardes, node: u64, h: u32, data: []const u8) th.Answer {
            return call(pp, .{ .tag = 4, .op = .write, .node = node, .handle = h, .data = data });
        }
    };
    const a = call(p, .{ .tag = 1, .op = .open, .node = ctl_node, .omode = 2 }).reply.handle;
    const b = call(p, .{ .tag = 2, .op = .open, .node = ctl_node, .omode = 1 }).reply.handle;
    try testing.expect(a != 0 and b != 0 and a != b);
    // Reading the status line holds nothing, so it cannot lock either.
    try testing.expectEqual(@as(u32, 0), call(p, .{ .tag = 3, .op = .open, .node = ctl_node }).reply.handle);
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "lock\n").errno());

    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\n").reply.status);
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\n").reply.status);
    // Another open's lock is refused at once, and so is its unlock; writes
    // to the pane's other files are not.
    try testing.expectEqualStrings(e_locked, w.ctl(p, ctl_node, b, "lock\n").reply.ename);
    try testing.expectEqual(E.BUSY, w.ctl(p, ctl_node, b, "lock\n").errno());
    try testing.expectEqualStrings(e_not_locked, w.ctl(p, ctl_node, b, "unlock\n").reply.ename);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .addr), "1").reply.status);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .data), "ONE\n").reply.status);
    try testing.expectEqualStrings("ONE\ntwo\n", p.panes[0].?.file.?.content);

    // Once the holder unlocks, the other's try takes it.
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "unlock\n").reply.status);
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, b, "lock\n").reply.status);
    try testing.expectEqual(E.BUSY, w.ctl(p, ctl_node, a, "lock\nunlock\n").errno());
    // Closing the holder gives it up.
    _ = call(p, .{ .tag = 5, .op = .release, .node = ctl_node, .handle = b });
    try testing.expectEqual(Status.ok, w.ctl(p, ctl_node, a, "lock\nunlock\nlock\n").reply.status);
    try testing.expectEqual(E.INVAL, w.ctl(p, ctl_node, a, "unlock\nunlock\n").errno());
    try testing.expectEqual(@as(?u32, a), p.panes[0].?.fs.lock);

    // The lock lives and dies with the pane.
    const other = try th.newPane(p);
    const other_ctl = Node.of(other, .ctl);
    const c = call(p, .{ .tag = 6, .op = .open, .node = other_ctl, .omode = 1 }).reply.handle;
    try testing.expectEqual(Status.ok, w.ctl(p, other_ctl, c, "lock\n").reply.status);
    try testing.expectEqual(Status.ok, th.rmdir(p, Node.of(other, .dir)).reply.status);
    try testing.expectEqual(E.NOENT, w.ctl(p, other_ctl, c, "lock\n").errno());
    for ([_]u64{ ctl_node, other_ctl }, [_]u32{ a, c }) |node, h|
        _ = call(p, .{ .tag = 7, .op = .release, .node = node, .handle = h });
    try testing.expect(p.panes[0].?.fs.lock == null);
    for (p.fs.opens) |o| try testing.expect(o.node == 0);
}

test "Edit through a pane's ctl renames every foo in one undo step, and a failed one changes nothing" {
    const p = try withFile(testing.allocator, "foo x foo y foo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Edit ,x/foo/c/foobar/\n").reply.status);
    try testing.expectEqualStrings("foobar x foobar y foobar\n", rd(p, body, 0, 64).bytes);
    const failed = wr(p, ctl_node, "Edit ,s/nothing/x/\n");
    try testing.expectEqual(E.IO, failed.errno());
    try testing.expectStringStartsWith(failed.reply.ename, "Edit: no substitution");
    try testing.expectEqualStrings("foobar x foobar y foobar\n", rd(p, body, 0, 64).bytes);
    // The whole rename is one undo step.
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Undo").reply.status);
    try testing.expectEqualStrings("foo x foo y foo\n", rd(p, body, 0, 64).bytes);
}

test "a write of an Edit block carries it whole, to a pane's ctl, the root's ctl and exec" {
    const p = try withFile(testing.allocator, "foo x\nfoo y\n");
    defer p.deinit();
    const serial = serialOf(p);
    const body = Node.of(serial, .body);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Edit ,x/foo/{\ni/[/\na/]/\n}\n").reply.status);
    try testing.expectEqualStrings("[foo] x\n[foo] y\n", rd(p, body, 0, 64).bytes);
    p.active = p.paneBySerial(serial).?;
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Edit ,x/\\[/{\nc/</\n}\n").reply.status);
    try testing.expectEqualStrings("<foo] x\n<foo] y\n", rd(p, body, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Edit $a\nend\n.\n").reply.status);
    try testing.expectEqualStrings("<foo] x\n<foo] y\nend\n", rd(p, body, 0, 64).bytes);
    // An unclosed group is refused, and nothing after it runs as a line.
    try testing.expectEqual(E.IO, wr(p, Node.of(serial, .ctl), "Edit ,x/foo/{\nd\n").errno());
    try testing.expectEqualStrings("<foo] x\n<foo] y\nend\n", rd(p, body, 0, 64).bytes);
}

test "dirty goes back to 0 when the text is the saved text again" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const dirty = Node.of(serial, .dirty);
    try testing.expectEqualStrings("0\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .body), "two\n").reply.status);
    try testing.expectEqualStrings("1\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Undo").reply.status);
    try testing.expectEqualStrings("0\n", rd(p, dirty, 0, 8).bytes);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Redo").reply.status);
    try testing.expectEqualStrings("1\n", rd(p, dirty, 0, 8).bytes);
}

test "a message from a root ctl write is the session's in the log" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.tick); // the pane's `new` is logged before the log is opened
    while (p.nextEffect()) |_| {}
    const log = @intFromEnum(tree.TopFile.log);
    const f = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    const frozen = call(p, .{ .tag = 2, .op = .read, .node = log, .handle = f, .size = 8192 }).bytes.len;
    _ = call(p, .{ .tag = 3, .op = .write, .node = log, .handle = f, .data = "follow" });
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Kill\n").reply.status);
    // What it said, the session's; its own words name it, so its Verbose
    // announcement gives way to them.
    try testing.expectEqualStrings("msg - Kill: nothing running\n", call(p, .{ .tag = 5, .op = .read, .node = log, .handle = f, .off = frozen, .size = 4096 }).bytes);
}

test "a look takes acme's :addr and file:addr, and a miss changes nothing" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "foo x foo y\nbar\n");
    defer p.deinit();
    const serial = serialOf(p);
    const look_node = Node.of(serial, .look);
    const dot = Node.of(serial, .dot);
    // :addr is an address in this pane, evaluated from its dot.
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/y/\n").reply.status);
    try testing.expectEqualStrings("         10          11 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, ":#4\n").reply.status);
    try testing.expectEqualStrings("          4           4 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/foo/\n").reply.status); // from #4: the second foo
    try testing.expectEqualStrings("          6           9 ", rd(p, dot, 0, 64).bytes);
    // file:addr names the pane's own file here.
    var line: [256]u8 = undefined;
    const path = p.panes[0].?.file.?.path;
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:/bar/\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          15 ", rd(p, dot, 0, 64).bytes);
    // A miss: no buffer, the selection kept, and it says so.
    const panes_before = p.panes.len - std.mem.count(?*pardes.Pane, &p.panes, &.{null});
    try testing.expectEqual(Status.ok, wr(p, look_node, "zzqq\n").reply.status);
    try testing.expectEqual(panes_before, p.panes.len - std.mem.count(?*pardes.Pane, &p.panes, &.{null}));
    try testing.expectEqualStrings("         12          15 ", rd(p, dot, 0, 64).bytes);
    try testing.expectStringStartsWith(p.panes[0].?.msg[0..p.panes[0].?.msg_len], "Look: no match");
    // A hit answers the pane the text is selected in, not its hits buffer.
    try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
    var own: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&own, "{d}\n", .{serial}), rd(p, look_node, 0, 64).bytes);
    // A pattern with a blank in it; 0/re/ searches from the top, whatever dot is.
    try testing.expectEqual(Status.ok, wr(p, look_node, ":/foo y/\n").reply.status);
    try testing.expectEqualStrings("          6          11 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:0/foo/\n", .{path})).reply.status);
    try testing.expectEqualStrings("          0           3 ", rd(p, dot, 0, 64).bytes);
    // file:N selects the line; a line past the end moves nothing and reads back empty.
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:2\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          16 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&line, "{s}:99\n", .{path})).reply.status);
    try testing.expectEqualStrings("         12          16 ", rd(p, dot, 0, 64).bytes);
    try testing.expectEqualStrings("", rd(p, look_node, 0, 64).bytes);
    try testing.expectStringStartsWith(p.panes[0].?.msg[0..p.panes[0].?.msg_len], "Look: ");
}

test "the root look's file:/re/ goes on from the dot, and a miss leaves the dot as it was" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "foo x foo y\nfoo\n");
    defer p.deinit();
    const dot = Node.of(serialOf(p), .dot);
    const root = @intFromEnum(tree.TopFile.look);
    var line: [256]u8 = undefined;
    const path = p.panes[0].?.file.?.path;
    const again = try std.fmt.bufPrint(&line, "{s}:/foo/\n", .{path});
    for ([_][]const u8{ "          0           3 ", "          6           9 ", "         12          15 ", "          0           3 " }) |want| {
        try testing.expectEqual(Status.ok, wr(p, root, again).reply.status);
        try testing.expectEqualStrings(want, rd(p, dot, 0, 64).bytes);
    }
    try testing.expectEqual(Status.ok, wr(p, root, try std.fmt.bufPrint(&line, "{s}:/zzqq/\n", .{path})).reply.status);
    try testing.expectEqualStrings("          0           3 ", rd(p, dot, 0, 64).bytes);
}

test "a look's miss repeats the path whole up to 256 bytes, then gives up its middle to an ellipsis" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root = @intFromEnum(tree.TopFile.look);
    const long = "some/deeply/nested/directory/that/goes/on/and/on/with/a_rather_long_file_name.txt";
    var line: [512]u8 = undefined;
    _ = wr(p, root, try std.fmt.bufPrint(&line, "{s}\n", .{long}));
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&line, "look: no match for \"{s}\"\n", .{long})));
    const huge = "é" ** 150; // 300 bytes: its middle cut to fit 256, between characters
    _ = wr(p, root, huge ++ "\n");
    try testing.expect(th.logHas(p, "look: no match for \"" ++ "é" ** 63 ++ "…" ++ "é" ** 63 ++ "\"\n"));
}

test "exec runs a builtin at the pane and records the pane it acted on" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg fs-ran\n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Msg from exec\n").reply.status);
    try testing.expectEqualStrings("from exec", pane.msg[0..pane.msg_len]);
    var expected: [16]u8 = undefined;
    const own = try std.fmt.bufPrint(&expected, "{d}\n", .{serial});
    try testing.expectEqualStrings(own, rd(p, root_exec, 0, 4096).bytes);
    // Either command file reads back what the last one did.
    try testing.expectEqualStrings(own, rd(p, Node.of(serial, .look), 0, 4096).bytes);
    try testing.expectEqual(@as(u64, own.len), call(p, .{ .tag = 1, .op = .getattr, .node = root_exec }).reply.attr.size);

    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "New\n").reply.status);
    const made = p.panes[p.active].?;
    try testing.expect(made.serial != serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, Node.of(made.serial, .exec), "Del\n").reply.status);
    try testing.expect(p.paneBySerial(made.serial) == null);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);
}

test "status reads the editor, and look and exec validate whole batches" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg root\n");
    defer p.deinit();
    const status = rd(p, root_status, 0, 4096);
    try testing.expectEqual(Status.ok, status.reply.status);
    var lines = std.mem.tokenizeScalar(u8, status.bytes, '\n');
    try testing.expect(std.mem.startsWith(u8, lines.next().?, "pid "));
    var expected: [64]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "version {s}", .{pardes.version}), lines.next().?);
    var live: usize = 0;
    for (p.panes) |slot| live += @intFromBool(slot != null);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "panes {d}", .{live}), lines.next().?);
    try testing.expect(lines.next() == null);
    const stat = call(p, .{ .tag = 1, .op = .getattr, .node = root_status });
    try testing.expectEqual(@as(u64, status.bytes.len), stat.reply.attr.size);
    try testing.expectEqual(@as(u16, 0o444), stat.reply.attr.mode);
    try testing.expectEqual(E.PERM, wr(p, root_status, "anything\n").errno());
    try testing.expectEqualStrings("", rd(p, root_exec, 0, 4096).bytes);

    const serial = p.next_serial;
    for ([_][]const u8{ "Msg a\x00b", "Msg x\nMsg \x01y\n" }) |invalid| {
        try testing.expectEqual(E.INVAL, wr(p, root_exec, invalid).errno());
        try testing.expectEqual(serial, p.next_serial);
    }
    // An empty write is a no-op, not a command.
    try testing.expectEqual(Status.ok, wr(p, root_exec, "\n \n").reply.status);
    try testing.expectEqualStrings("", rd(p, root_exec, 0, 4096).bytes);
    try testing.expectEqualStrings(status.bytes, rd(p, root_status, 0, 4096).bytes);

    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Msg hello there\n").reply.status);
    try testing.expectEqualStrings("hello there", pane.msg[0..pane.msg_len]);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{pane.serial}), rd(p, root_exec, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_look, "/virtual/index\n").reply.status);
    const opened = p.panes[p.active].?;
    try testing.expectEqualStrings("/virtual/index", opened.file.?.path);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);

    try testing.expectEqual(Status.ok, wr(p, root_exec, "New\n").reply.status);
    const made = p.panes[p.active].?;
    try testing.expect(made.serial != opened.serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{made.serial}), rd(p, root_exec, 0, 4096).bytes);
}

test "look opens spaced paths and locations without editing the source pane" {
    if (!fs.platform_has_fs) return error.SkipZigTest;
    const gpa = testing.allocator;
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "two words.zig", .data = "first\nsecond\nthird\n" });
    var path_buf: [4096]u8 = undefined;
    const path = path_buf[0..try tmp.dir.realPathFile(testing.io, "two words.zig", &path_buf)];
    const p = try withFile(gpa, "source stays intact\n");
    defer p.deinit();
    const source = p.panes[0].?;
    const look_node = Node.of(source.serial, .look);
    const revision = source.file.?.revision;
    const undo_len = source.file.?.history.undo_len;
    source.body.cur_col = 3;
    var clicked: [4200]u8 = undefined;
    try testing.expectEqual(Status.ok, wr(p, look_node, try std.fmt.bufPrint(&clicked, "{s}:2:3\n", .{path})).reply.status);
    const opened = p.panes[p.active].?;
    try testing.expect(opened != source);
    try testing.expectEqualStrings(path, opened.file.?.path);
    try testing.expectEqualStrings("first\nsecond\nthird\n", opened.file.?.content);
    try testing.expectEqual(@as(i32, 1), opened.body.cur_row);
    try testing.expectEqual(@as(i32, 2), opened.body.cur_col);
    try testing.expectEqualStrings("source stays intact\n", source.file.?.content);
    try testing.expectEqual(revision, source.file.?.revision);
    try testing.expectEqual(undo_len, source.file.?.history.undo_len);
    try testing.expectEqual(@as(i32, 3), source.body.cur_col);
    var expected: [16]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);

    p.active = 0;
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&clicked, "{s}:3:2\n", .{path})).reply.status);
    try testing.expect(p.panes[p.active].? == opened);
    try testing.expectEqual(@as(i32, 2), opened.body.cur_row);
    try testing.expectEqual(@as(i32, 1), opened.body.cur_col);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&expected, "{d}\n", .{opened.serial}), rd(p, root_look, 0, 4096).bytes);
}

test "look validates the whole batch before opening virtual files" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "source\n");
    defer p.deinit();
    const source = p.panes[0].?;
    const look_node = Node.of(source.serial, .look);
    const serial = p.next_serial;
    for ([_][]const u8{
        "/virtual/index\x00ignored", "/virtual/index\n/virtual/\x01index\n",
    }) |invalid| {
        try testing.expectEqual(E.INVAL, wr(p, look_node, invalid).errno());
        try testing.expectEqual(serial, p.next_serial);
        try testing.expectEqual(@as(usize, 0), p.active);
        try testing.expectEqualStrings("source\n", source.file.?.content);
    }
    try testing.expectEqual(Status.ok, wr(p, look_node, "/n/self/index\n").reply.status);
    const opened = p.panes[p.active].?;
    try testing.expectEqualStrings("/virtual/index", opened.file.?.path);
    try testing.expect(std.mem.indexOf(u8, opened.file.?.content, "/test.txt") != null);
    try testing.expectEqualStrings("source\n", source.file.?.content);
}

test "get reloads the pane from disk and reports a missing file without losing dirty contents" {
    const gpa = testing.allocator;
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "note.txt", .data = "from disk\n" });
    var directory_buf: [4096]u8 = undefined;
    const directory = directory_buf[0..try tmp.dir.realPath(testing.io, &directory_buf)];
    var path_buf: [4096]u8 = undefined;
    const path = try std.fmt.bufPrint(&path_buf, "{s}/note.txt", .{directory});

    const p = try withFile(gpa, "in memory\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const pane = p.panes[0].?;

    var name: [std.fs.max_path_bytes + 8]u8 = undefined;
    _ = wr(p, Node.of(serial, .name), try std.fmt.bufPrint(&name, "{s}\n", .{path}));
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "get\n").reply.status);
    try testing.expectEqualStrings("from disk\n", pane.file.?.content);
    try testing.expect(!pane_files.dirtyOf(pane));
    try testing.expect(pane.file.?.history.undo_len > 0);
    // Renamed but never edited, it was clean: nothing thrown away, nothing
    // logged as reloaded over edits.
    var reloaded: [32]u8 = undefined;
    try testing.expect(!th.logHas(p, try std.fmt.bufPrint(&reloaded, "changed {d} reloaded\n", .{serial})));

    _ = wr(p, Node.of(serial, .name), try std.fmt.bufPrint(&name, "{s}/missing.txt\n", .{directory}));
    _ = wr(p, Node.of(serial, .body), "unsaved\n");
    // Unsaved text is asked about once, as acme's get asks winclean.
    const asked = wr(p, ctl_node, "get\n");
    try testing.expectEqual(E.IO, asked.errno());
    try testing.expect(std.mem.endsWith(u8, asked.reply.ename, ": Modified (get again to discard)"));
    var unsaved: [4200]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&unsaved, "unsaved {d} {s}/missing.txt\n", .{ serial, directory })));
    try testing.expectEqual(E.NOENT, wr(p, ctl_node, "get\n").errno());
    try testing.expect(p.paneBySerial(serial) != null);
    try testing.expectEqualStrings("from disk\nunsaved\n", pane.file.?.content);
    try testing.expect(pane_files.dirtyOf(pane));
}

test "a body write to a terminal is typed input, not a paste, even to a program that asked for bracketed paste" {
    const p = try Pardes.init(testing.allocator, .{ .cols = 90, .rows = 30 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const term = for (p.panes, 0..) |slot, id| {
        if (slot) |pane| if (pane.isTerminal()) break id;
    } else return error.SkipZigTest;
    p.update(.{ .output = .{ .pane = @intCast(term), .bytes = "\x1b[?2004h" } });
    while (p.nextEffect()) |_| {}
    const w = wr(p, Node.of(p.panes[term].?.serial, .body), "ls\n");
    try testing.expectEqual(Status.ok, w.reply.status);
    try testing.expectEqualStrings("ls\n", w.pty_buf[0..w.pty_len]);
}

test "Save path of a file pane logs a save record naming that path" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const saved = wr(p, Node.of(serial, .ctl), "Save /tmp/pardes-save-copy.txt\n");
    try testing.expectEqual(Status.ok, saved.reply.status);
    p.perform(.{ .save_text = .{ .pane = 0, .serial = serial, .path = Pardes.SavePath.from("/tmp/pardes-save-copy.txt") } });
    var want: [64]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "save {d} /tmp/pardes-save-copy.txt\n", .{serial})));
}

test "Mount with no dial is wrong #args, and a dial that is no address says bad dial address" {
    if (comptime !pardes.hosted) return;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const bare = wr(p, root_ctl, "Mount work\n");
    try testing.expectEqual(E.INVAL, bare.errno());
    try testing.expectStringStartsWith(bare.reply.ename, "wrong #args");
    const bad = wr(p, root_ctl, "Mount work tcp!nohost\n");
    try testing.expectEqual(E.INVAL, bad.errno());
    try testing.expectStringStartsWith(bad.reply.ename, "Mount: bad dial address: tcp!nohost");
    try testing.expectEqual(@as(usize, 0), p.fs.mounts.items.len);
}

test "an address looked at in an image pane names the image, never an empty subject" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const id = p.freeSlot().?;
    const doc = try p.newDocPane(id);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    _ = wr(p, Node.of(doc.serial, .look), ":/x/\n");
    try testing.expect(th.logHas(p, "look: /tmp/pardes-pic.ppm is no text to address"));
}

test "Save and Save path on an image pane are refused with why, never a silent success" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const id = p.freeSlot().?;
    const doc = try p.newDocPane(id);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    for ([_][]const u8{ "Save\n", "Save /tmp/pardes-copy.ppm\n" }) |line| {
        const r = wr(p, Node.of(doc.serial, .ctl), line);
        try testing.expectEqual(Status.err, r.reply.status);
        try testing.expectEqualStrings("Save: an image pane has no text to save", r.reply.ename);
    }
}

test "a builtin for one kind of pane is refused on another, and still acts on its own kind" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "text\n");
    defer p.deinit();
    const serial = serialOf(p);
    const cases = [_]struct { []const u8, []const u8 }{
        .{ "Petscii\n", "Petscii: only an image or a terminal pane takes it" },
        .{ "Palette\n", "Palette: only an image pane takes it" },
        .{ "Ascii\n", "Ascii: only an image pane takes it" },
        .{ "Filter\n", "Filter: only a terminal pane takes it" },
        .{ "Togglettymode\n", "Togglettymode: only a terminal pane takes it" },
    };
    for (cases) |case| {
        const r = wr(p, Node.of(serial, .ctl), case[0]);
        try testing.expectEqual(Status.err, r.reply.status);
        try testing.expectEqualStrings(case[1], r.reply.ename);
    }
    if (pardes.pdf_enabled) for ([_][]const u8{ "PdfFit\n", "PdfTint\n", "PdfSections\n" }) |line| {
        try testing.expectEqual(Status.err, wr(p, Node.of(serial, .ctl), line).reply.status);
    };
    const id = p.freeSlot().?;
    const doc = try p.newDocPane(id);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    const r = wr(p, Node.of(doc.serial, .ctl), "Mode\n");
    try testing.expectEqualStrings("Mode: only a text or terminal pane has modes", r.reply.ename);
    const glyphs = doc.image.?.glyph_art;
    try testing.expectEqual(Status.ok, wr(p, Node.of(doc.serial, .ctl), "Petscii\n").reply.status);
    try testing.expect(doc.image.?.glyph_art != glyphs);
}

test "exec Save writes the named file through the host" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "one\ntwo\n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[0].?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .name), "/tmp/renamed.txt\n").reply.status);
    try testing.expect(!pane_files.dirtyOf(pane)); // a name alone is no edit; Save writes all the same
    const saved = wr(p, Node.of(serial, .exec), "Save\n");
    try testing.expectEqual(Status.ok, saved.reply.status);
    try testing.expect(saved.saved);
    p.perform(.{ .save_file = .{ .pane = 0 } });
    try testing.expect(!pane_files.dirtyOf(pane));
    try testing.expectEqualStrings(pane.file.?.content, p.fallback.get("/tmp/renamed.txt").?);
}

test "a refusal's +Unsaved goes in the session's directory when the active pane's directory is not there" {
    if (comptime !pardes.hosted) return;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .name), "/tmp/pardes-no-such-dir-zz/x.txt\n").reply.status);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .body), "edited\n").reply.status);
    try testing.expectEqual(Status.err, wr(p, @intFromEnum(tree.TopFile.ctl), "Exit\n").reply.status);
    const unsaved = for (p.panes) |slot| {
        const pane = slot orelse continue;
        const f = pane.file orelse continue;
        if (f.output) |o| if (o.from == .unsaved) break f.path;
    } else return error.NoUnsavedPane;
    try testing.expectEqualStrings(p.sessionDir(), std.fs.path.dirname(unsaved).?);
}

test "a look at a file it may not read fails the write naming the file" {
    if (comptime !pardes.hosted) return;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "locked.txt", .data = "secret\n", .flags = .{ .permissions = .fromMode(0o000) } });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const path = try std.fmt.bufPrint(&line, "{s}/locked.txt", .{dir});
    var want: [4200]u8 = undefined;
    const expected = try std.fmt.bufPrint(&want, "look: {s}: permission denied", .{path});
    var with_newline: [4300]u8 = undefined;
    const refused = wr(p, root_look, try std.fmt.bufPrint(&with_newline, "{s}\n", .{path}));
    if (refused.reply.status == .ok) return error.SkipZigTest; // root reads anything
    try testing.expectEqualStrings(expected, refused.reply.ename);
}

test "Pager is a setting of the root ctl: pardes by default, off taken, anything else refused with its choices" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "Pager pardes\n") != null);
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Pager off\n").reply.status);
    try testing.expectEqual(config.Runtime.Pager.off, p.settings.pager);
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "Pager off\n") != null);
    try testing.expectEqualStrings("bad value in control message; takes pardes, off \"less\"", wr(p, root_ctl, "Pager less\n").reply.ename);
}

test "a bad setting value is quoted, so two different bad values log as two records, never one counted twice" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    _ = wr(p, root_ctl, "Verbose maybe\n");
    _ = wr(p, root_ctl, "Verbose nope\n");
    try testing.expect(th.logHas(p, "takes on, off \"maybe\"\n"));
    try testing.expect(th.logHas(p, "takes on, off \"nope\"\n"));
    try testing.expect(!th.logHas(p, "(x2)"));
}

test "a look line's trailing colon is dropped, and a look whose address fails never leaves its file open" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = "one\ntwo\nthree\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const count = struct {
        fn of(pp: *Pardes) usize {
            var n: usize = 0;
            for (pp.panes) |slot| n += @intFromBool(slot != null);
            return n;
        }
    }.of;
    const before = count(p);
    // Failing addresses: nothing opened, the write still answered.
    inline for ([_][]const u8{ "{s}/a.txt:/nomatch/\n", "{s}/a.txt:9:\n" }) |fmt| {
        _ = wr(p, root_look, try std.fmt.bufPrint(&line, fmt, .{dir}));
        try testing.expectEqual(before, count(p));
    }
    // `a.txt:2:3:` is `a.txt:2:3`: it opens there.
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt:2:3:\n", .{dir})).reply.status);
    try testing.expectEqual(before + 1, count(p));
    const opened = p.panes[p.active].?;
    try testing.expect(std.mem.endsWith(u8, opened.file.?.path, "/a.txt"));
    try testing.expectEqual(@as(i32, 1), opened.body.cur_row);
}

test "a bare :N or :N:M look addresses the pane itself, from its look, the root's and event write-back" {
    const p = try withFile(testing.allocator, "alpha\nbeta\ngamma\n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[p.paneBySerial(serial).?].?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), ":2\n").reply.status);
    try testing.expectEqual(pane_files.State.Range{ .q0 = 6, .q1 = 11 }, pane_files.dotOf(pane));
    try testing.expectEqual(Status.ok, wr(p, root_look, ":3\n").reply.status);
    try testing.expectEqual(pane_files.State.Range{ .q0 = 11, .q1 = 17 }, pane_files.dotOf(pane));
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), ":3:2\n").reply.status);
    try testing.expectEqual(@as(u32, 12), pane_files.dotOf(pane).q0);
    // Written back by an event reader, the same.
    const event = Node.of(serial, .event);
    const h = call(p, .{ .tag = 1, .op = .open, .node = event }).reply.handle;
    defer _ = call(p, .{ .tag = 9, .op = .release, .node = event, .handle = h });
    try testing.expectEqual(Status.ok, wr(p, event, "ML0 0 0 2 :1\n").reply.status);
    try testing.expectEqual(pane_files.State.Range{ .q0 = 0, .q1 = 6 }, pane_files.dotOf(pane));
}

test "a refused Del written back through event fails that write, EIO, with its err" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "text\n");
    defer p.deinit();
    const serial = serialOf(p);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .body), "more\n").reply.status); // unsaved
    const event = Node.of(serial, .event);
    const h = call(p, .{ .tag = 1, .op = .open, .node = event }).reply.handle;
    defer _ = call(p, .{ .tag = 9, .op = .release, .node = event, .handle = h });
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Del\n").reply.status);
    const record = call(p, .{ .tag = 2, .op = .read, .node = event, .handle = h, .size = 256 }).bytes;
    var copy: [256]u8 = undefined;
    @memcpy(copy[0..record.len], record);
    const back = wr(p, event, copy[0..record.len]);
    try testing.expectEqual(E.IO, back.errno());
    try testing.expect(std.mem.indexOf(u8, back.reply.ename, "Modified") != null);
    try testing.expect(p.paneBySerial(serial) != null);
}

test "a pane's own look and exec go to the event reader holding it, which writes them back to act" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "Msg routed\n");
    defer p.deinit();
    const serial = serialOf(p);
    const event = Node.of(serial, .event);
    const h = call(p, .{ .tag = 1, .op = .open, .node = event }).reply.handle;
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .exec), "Msg routed\n").reply.status);
    // Not done: the reader has it, as it would a middle click.
    const pane = p.panes[0].?;
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "routed") == null);
    const record = call(p, .{ .tag = 2, .op = .read, .node = event, .handle = h, .size = 256 }).bytes;
    // Flag 1: its first word is a builtin; no 2, no expansion follows.
    try testing.expectEqualStrings("FX0 0 1 10 Msg routed\n", record);
    // Written back, it is done.
    try testing.expectEqual(tree.Status.ok, wr(p, event, record).reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "routed") != null);
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .look), "one.txt:3\n").reply.status);
    try testing.expectEqualStrings("FL0 0 4 9 one.txt:3\n", call(p, .{ .tag = 3, .op = .read, .node = event, .handle = h, .size = 256 }).bytes);
    // The root's is a click at the pane with the keyboard, this one.
    try testing.expectEqual(tree.Status.ok, wr(p, root_exec, "Msg rooted\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "rooted") == null);
    try testing.expectEqualStrings("FX0 0 1 10 Msg rooted\n", call(p, .{ .tag = 5, .op = .read, .node = event, .handle = h, .size = 256 }).bytes);
    // A click in its tag is the reader's too, an `x` record, as acme's is;
    // written back, it is done.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .tagexec), "Msg tagged\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "tagged") == null);
    const tagged = call(p, .{ .tag = 6, .op = .read, .node = event, .handle = h, .size = 256 }).bytes;
    try testing.expectEqualStrings("Fx0 0 1 10 Msg tagged\n", tagged);
    try testing.expectEqual(tree.Status.ok, wr(p, event, tagged).reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "tagged") != null);
    _ = call(p, .{ .tag = 4, .op = .release, .node = event, .handle = h });
    // With no reader, the root's and the pane's act at once.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .exec), "Msg direct\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "direct") != null);
}

test "look and exec read back what the last command touched, a ctl write's too" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    var want: [32]u8 = undefined;
    _ = wr(p, root_exec, "Msg first\n");
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{serial}), rd(p, root_exec, 0, 64).bytes);
    // A pane made through ctl is what both read next, not the Msg's pane.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(serial, .ctl), "Tty\n").reply.status);
    const made = p.panes[p.active].?.serial;
    try testing.expect(made != serial);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, root_exec, 0, 64).bytes);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, @intFromEnum(tree.TopFile.look), 0, 64).bytes);
    // A ctl write that makes nothing names the pane it ran at.
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Verbose off\n").reply.status);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{d}\n", .{made}), rd(p, root_exec, 0, 64).bytes);
    // Closed, it is no pane to go to: a fresh read of look is empty.
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(made, .ctl), "Del\n").reply.status);
    try testing.expect(p.paneBySerial(made) == null);
    try testing.expectEqualStrings("", rd(p, @intFromEnum(tree.TopFile.look), 0, 64).bytes);
}

test "a builtin's Verbose announcement is logged only when it succeeds, its failure said now or by the host later" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    var want: [64]u8 = undefined;
    const said_exit = try std.fmt.bufPrint(&want, "msg {d} Exit\n", .{serial});
    // A Save a ctl write gives no name to, on a scratch: refused, no Save.
    const scratch = try th.newPane(p);
    var said_save_buf: [64]u8 = undefined;
    try testing.expectEqual(E.INVAL, wr(p, Node.of(scratch, .ctl), "Save\n").errno());
    try testing.expect(!th.logHas(p, try std.fmt.bufPrint(&said_save_buf, "msg {d} Save\n", .{scratch})));
    // Refused as it runs, through a click: the write fails, and no Exit.
    const f = &p.panes[0].?.file.?;
    f.saved_revision = f.revision -% 1;
    f.saved_hash = 0;
    try testing.expect(wr(p, Node.of(serial, .exec), "Exit\n").errno() != 0);
    try testing.expect(!th.logHas(p, said_exit));
    // Refused at the keyboard (no write to fail), edited since: the same.
    f.revision +%= 1;
    _ = p.executeBuiltinLine(p.active, "Exit");
    try testing.expect(!th.logHas(p, said_exit));
    try testing.expect(!p.quit);
    // A Save the host could not do, told a step later: the Save goes too.
    var save_buf: [64]u8 = undefined;
    const said_save = try std.fmt.bufPrint(&save_buf, "msg {d} Save\n", .{serial});
    _ = wr(p, Node.of(serial, .exec), "Save\n");
    p.saveFailed(@intCast(p.paneBySerial(serial).?), "/test.txt", error.AccessDenied);
    try testing.expect(!th.logHas(p, said_save));
    // One that does what it says keeps its announcement.
    _ = wr(p, Node.of(serial, .exec), "Undo\n");
    var undo_buf: [64]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&undo_buf, "msg {d} Undo", .{serial})));
}

test "an error's words give the errno a mount reads: EINVAL for what is malformed, EIO for what failed" {
    // 9ns (cloud9's 9ns/src/nine.zig) maps an error to an errno by its
    // words, and EIO when none of them match: these words must not.
    const addressing = @import("addr.zig");
    const einval = [_][]const u8{ "control message", "invalid", "bad " };
    const other = [_][]const u8{ "interrupt", "shut down", "not exist", "not found", "no such", "exists", "not empty", "not a dir", "is a dir", "permission", "denied", "read-only", "read only", "no space", "not allowed", "not permitted", "cannot", "fid", "busy", "in use", "too long", "not supported", "unsupported" };
    const Case = struct { text: []const u8, malformed: bool };
    for ([_]Case{
        .{ .text = addressing.e_syntax, .malformed = true },
        .{ .text = addressing.e_regexp, .malformed = true },
        .{ .text = e_prompt, .malformed = true },
        .{ .text = addressing.e_no_match, .malformed = false },
        .{ .text = addressing.e_range, .malformed = false },
        .{ .text = addressing.e_order, .malformed = false },
        .{ .text = addressing.e_slow, .malformed = false },
        .{ .text = "/tmp/x.txt: Modified (Exit again to discard)", .malformed = false },
        .{ .text = "Edit: w is a sam command pardes's Edit leaves out (it has no file or shell commands)", .malformed = false },
    }) |c| {
        const says_einval = for (einval) |w| {
            if (std.ascii.findIgnoreCase(c.text, w) != null) break true;
        } else false;
        try testing.expectEqual(c.malformed, says_einval);
        for (other) |w| try testing.expect(std.ascii.findIgnoreCase(c.text, w) == null);
    }
}

test "DumpConfig's whole report writes back to the root ctl, line by line, with no error" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "DumpConfig\n").reply.status);
    const report = for (p.panes) |slot| {
        const pane = slot orelse continue;
        const f = pane.file orelse continue;
        const o = f.output orelse continue;
        if (std.meta.eql(o.from, panes.Output.Origin{ .cmd = .DumpConfig })) break try testing.allocator.dupe(u8, f.content);
    } else return error.NoDumpConfigPane;
    defer testing.allocator.free(report);
    // What this shell cannot show is a comment, never a value it refuses.
    if (pardes.platform == .tty) try testing.expect(std.mem.indexOf(u8, report, "# GripWidth unsupported\n") != null);
    var lines = std.mem.splitScalar(u8, report, '\n');
    while (lines.next()) |line| {
        if (line.len == 0) continue;
        const r = wr(p, root_ctl, line);
        if (r.reply.status != .ok) std.debug.print("refused: {s}: {s}\n", .{ line, r.reply.ename });
        try testing.expectEqual(Status.ok, r.reply.status);
    }
}

test "a Restore asks again for the ThemeFile the dump names, as a /ctl write of it does" {
    if (comptime !pardes.hosted) return;
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const good = "/tmp/pardes-restored-theme.zon";
    _ = wr(p, @intFromEnum(tree.TopFile.ctl), "ThemeFile " ++ good ++ "\n");
    var custom = pardes.themes[0];
    custom.name = "restored";
    var encoded: std.Io.Writer.Allocating = .init(gpa);
    defer encoded.deinit();
    try std.zon.stringify.serialize(custom, .{}, &encoded.writer);
    try testing.expect(pardes.colors.loadThemeFile(p, p.theme_file_generation, encoded.written(), false));
    try pardes.dump.dumpState(p);
    const restored = try pardes.dump.restore(p, p.dump_out.?, "/tmp/pardes.dump.zon");
    defer restored.deinit();
    const asked = while (restored.nextEffect()) |effect| switch (effect) {
        .theme_file => |t| if (t.on) break t,
        else => {},
    } else return error.NoThemeFileAsked;
    try testing.expectEqualStrings(good, pardes.colors.themeFileRequest(restored, asked.generation).?.path);
    // The file broken since, the load fails: the restored session still
    // shows the theme the old one did, and names the file it loaded.
    try testing.expectEqualStrings("restored", restored.theme().name);
    pardes.colors.failThemeFile(restored, asked.generation, error.ParseZon);
    try testing.expectEqualStrings("restored", restored.theme().name);
    try testing.expectEqualStrings(good, restored.theme_file_path.get());
}

test "a ThemeFile that fails to load changes nothing: the root ctl still names the one loaded, or none" {
    if (comptime !pardes.hosted) return;
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    // None loaded: a failed one leaves Theme as it was.
    _ = wr(p, root_ctl, "ThemeFile /tmp/pardes-no-such-theme.zon\n");
    pardes.colors.failThemeFile(p, p.theme_file_generation, error.FileNotFound);
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "ThemeFile") == null);
    try testing.expectEqualStrings("", p.theme_file_path.get());
    // One loaded, then another that fails: still the first, on every read.
    const good = "/tmp/pardes-good-theme.zon";
    _ = wr(p, root_ctl, "ThemeFile " ++ good ++ "\n");
    var custom = pardes.themes[0];
    custom.name = "good";
    var encoded: std.Io.Writer.Allocating = .init(gpa);
    defer encoded.deinit();
    try std.zon.stringify.serialize(custom, .{}, &encoded.writer);
    try testing.expect(pardes.colors.loadThemeFile(p, p.theme_file_generation, encoded.written(), false));
    _ = wr(p, root_ctl, "ThemeFile /tmp/pardes-bad-theme.zon\n");
    try testing.expect(!pardes.colors.loadThemeFile(p, p.theme_file_generation, ".{ .name = ", false));
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, "ThemeFile " ++ good ++ "\n") != null);
    try testing.expectEqualStrings(good, p.theme_file_path.get());
}

test "after a ThemeFile the root ctl and DumpConfig say ThemeFile and its path, which writes back" {
    if (comptime !pardes.hosted) return;
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const path = "/tmp/pardes-mine-theme.zon";
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "ThemeFile " ++ path ++ "\n").reply.status);
    var custom = pardes.themes[0];
    custom.name = "mine";
    var encoded: std.Io.Writer.Allocating = .init(gpa);
    defer encoded.deinit();
    try std.zon.stringify.serialize(custom, .{}, &encoded.writer);
    try testing.expect(pardes.colors.loadThemeFile(p, p.theme_file_generation, encoded.written(), false));
    const settings = rd(p, root_ctl, 0, 1 << 16).bytes;
    try testing.expect(std.mem.indexOf(u8, settings, "ThemeFile " ++ path ++ "\n") != null);
    try testing.expect(std.mem.indexOf(u8, settings, "Theme mine") == null);
    var storage: [16384]u8 = undefined;
    var out: std.Io.Writer = .fixed(&storage);
    try config.Runtime.writeReport(&out, .{
        .startup_config_path = null,
        .platform = @tagName(pardes.platform),
        .theme_name = p.theme().name,
        .theme_file = pardes.colors.loadedThemeFile(p),
        .compiled_default_shell = config.defaultShell(),
        .hover_delay_frames = null,
        .native_images = false,
        .capabilities = builtins.capabilities,
        .state = &p.settings,
    });
    try testing.expect(std.mem.indexOf(u8, out.buffered(), "ThemeFile " ++ path ++ "\n") != null);
    // Written back, it is the same request again, not "no theme mine".
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "ThemeFile " ++ path ++ "\n").reply.status);
}

test "Joincol with no column to the right and Theme with no such theme say so" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const joined = wr(p, root_ctl, "Joincol\n");
    try testing.expectEqual(tree.Status.err, joined.reply.status);
    try testing.expectStringStartsWith(joined.reply.ename, "Joincol: no column to the right");
    const themed = wr(p, root_ctl, "Theme drak\n");
    try testing.expectEqual(E.INVAL, themed.errno());
    try testing.expectStringStartsWith(themed.reply.ename, "bad value in control message; like it: ");
    try testing.expect(std.mem.indexOf(u8, themed.reply.ename, ": dr") != null);
    try testing.expect(std.mem.endsWith(u8, themed.reply.ename, "\"drak\""));
    // A click on the word says it on the message row.
    _ = wr(p, Node.of(serialOf(p), .exec), "Theme drak\n");
    const pane = p.panes[p.active].?;
    try testing.expect(std.mem.indexOf(u8, pane.msg[0..pane.msg_len], "no theme \"drak\"") != null);
    // Within the 128 bytes an Rerror carries, the quoted line kept.
    try testing.expect(themed.reply.ename.len <= 128);
    // A name in any case is the theme.
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Theme DRACULA\n").reply.status);
    try testing.expectEqualStrings("dracula", pardes.themes[p.settings.theme].name);
    // A misspelling far from any first letter's list still finds its like.
    var near: [170]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, pardes.colors.themesNear(&near, "9dracula"), "dracula") != null);
    // Every theme sharing the first letter, when they fit.
    var tested = false;
    for ("abcdefghijklmnopqrstuvwxyz") |letter| {
        var count: usize = 0;
        var len: usize = 0;
        for (pardes.themes) |t| if (t.name[0] == letter) {
            count += 1;
            len += t.name.len + 1;
        };
        if (count < 2 or len > near.len) continue;
        try testing.expectEqual(count, std.mem.count(u8, pardes.colors.themesNear(&near, &.{letter}), " ") + 1);
        tested = true;
    }
    try testing.expect(tested);
}

test "a look after Newcol fills the empty column the keyboard is on" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "file\n" });
    var dir: [4096]u8 = undefined;
    const at = dir[0..try tmp.dir.realPath(testing.io, &dir)];
    var line: [4200]u8 = undefined;
    // Newcol makes an empty column and gives its tag the keyboard; no pane
    // has it, so focus reads empty.
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Newcol\n").reply.status);
    try testing.expectEqual(@as(usize, 0), p.col_n[p.ncol - 1]);
    try testing.expectEqualStrings("", rd(p, @intFromEnum(tree.TopFile.focus), 0, 64).bytes);
    try testing.expectEqual(tree.Status.ok, wr(p, @intFromEnum(tree.TopFile.look), try std.fmt.bufPrint(&line, "{s}/f.txt\n", .{at})).reply.status);
    try testing.expectEqual(@as(usize, 1), p.col_n[p.ncol - 1]);
    try testing.expectEqual(p.active, p.col_panes[p.ncol - 1][0]);
}

test "a look at file:addr whose file is not there is one miss, quoting what was written, in a terminal too" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const looked = Node.of(serialOf(p), .look);
    for ([_][]const u8{ "zzq:#3", "zzq:2", "zzq:/re/" }) |written| {
        var line: [64]u8 = undefined;
        _ = wr(p, looked, try std.fmt.bufPrint(&line, "{s}\n", .{written}));
        var want: [64]u8 = undefined;
        try testing.expectEqual(@as(usize, 1), th.logCount(p, try std.fmt.bufPrint(&want, "look: no match for \"{s}\"\n", .{written})));
    }
    try testing.expectEqual(@as(usize, 3), th.logCount(p, "\nerr "));
}

test "a look whose pane is refused a place fails with that alone, not a missing line too" {
    const gpa = testing.allocator;
    // A screen with rows for one pane only.
    const p = try Pardes.init(gpa, .{ .tty_only = true, .cols = 80, .rows = 5 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    _ = try p.setTestFile("x\n");
    while (p.nextEffect()) |_| {}
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "one\ntwo\n" });
    var dir: [4096]u8 = undefined;
    const at = dir[0..try tmp.dir.realPath(testing.io, &dir)];
    var line: [4200]u8 = undefined;
    const r = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/f.txt:2\n", .{at}));
    try testing.expectEqual(Status.err, r.reply.status);
    try testing.expect(std.mem.indexOf(u8, r.reply.ename, "no space for a pane") != null);
    try testing.expectEqual(@as(usize, 1), th.logCount(p, "\nerr "));
}

test "a look under pardes's placement, from a pane pane/new made after Delcol, opens its file" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "file\n" });
    var dir: [4096]u8 = undefined;
    const at = dir[0..try tmp.dir.realPath(testing.io, &dir)];
    var line: [4200]u8 = undefined;
    const first = serialOf(p);
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(first, .exec), "Placement\n").reply.status);
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(first, .exec), "Delcol\n").reply.status);
    const made = try th.newPane(p);
    try testing.expectEqual(tree.Status.ok, wr(p, Node.of(made, .look), try std.fmt.bufPrint(&line, "{s}/f.txt:#4\n", .{at})).reply.status);
    // The pane pane/new made is placed, and so is the one its look opened.
    for (p.panes, 0..) |slot, i| if (slot != null) try testing.expect(layout.findPane(p, i) != null);
    try testing.expect(p.panes[p.active].?.serial != made);
}

test "a Restore of a file that is no dump fails the write before any warning, and a failed Dump fails its write" {
    if (comptime !pardes.hosted) return error.SkipZigTest;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const f = pane_files.fileOf(p.panes[0].?).?;
    f.content = try p.gpa.realloc(f.content, 3);
    @memcpy(f.content, "yy\n");
    f.revision +%= 1; // unsaved: a Restore would warn about it first
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "notes.txt", .data = "just notes\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line_buf: [4200]u8 = undefined;
    const line = try std.fmt.bufPrint(&line_buf, "Restore {s}/notes.txt\n", .{dir});
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const refused = wr(p, root_ctl, line);
    try testing.expectEqual(E.IO, refused.errno());
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "not a pardes dump: line 1: ") != null);
    try testing.expect(p.restore_req == null);
    try testing.expect(p.panes[0].?.discard_warned == null);

    p.fs.late_failure_len = 0;
    p.dumpFailed("/nowhere/pardes.dump.zon", error.FileNotFound);
    try testing.expectEqualStrings("Dump /nowhere/pardes.dump.zon: no such directory", p.fs.late_failure[0..p.fs.late_failure_len]);
    // A DumpDir that is there but no directory says that.
    p.fs.late_failure_len = 0;
    p.dumpFailed("/dev/null/pardes.dump.zon", error.NotDir);
    try testing.expectEqualStrings("Dump /dev/null/pardes.dump.zon: /dev/null is not a directory", p.fs.late_failure[0..p.fs.late_failure_len]);
}

test "a setting this frontend cannot show says GUI-only, and DumpDir reads back the directory in effect" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    if (!builtins.capabilities.lift) {
        try testing.expectEqualStrings("Lift is GUI-only, invalid here \"Lift\"", wr(p, root_ctl, "Lift on\n").reply.ename);
        try testing.expectEqualStrings("GripWidth is GUI-only, invalid here \"GripWidth\"", wr(p, root_ctl, "GripWidth 120\n").reply.ename);
        // A builtin the GUI alone has, written to a ctl or an exec, never
        // runs as a shell command.
        if (comptime !pardes.font_picker) {
            try testing.expectEqualStrings("Fonts is GUI-only, invalid here \"Fonts\"", wr(p, root_ctl, "Fonts\n").reply.ename);
            const ran = wr(p, root_exec, "Fonts\n");
            try testing.expectEqual(E.IO, ran.errno());
            try testing.expectEqualStrings("Fonts is GUI-only, invalid here", ran.reply.ename);
        }
    }
    try testing.expectEqualStrings("unknown control message \"Liftt\"", wr(p, root_ctl, "Liftt on\n").reply.ename);
    var buf: [900]u8 = undefined;
    if (pardes.dump.directory(&buf, "")) |dir| {
        var want: [920]u8 = undefined;
        const line = try std.fmt.bufPrint(&want, "\nDumpDir {s}\n", .{dir});
        try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 1 << 16).bytes, line) != null);
    }
}

test "Shell refuses a path that is no executable, and bare it goes back to the default" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const refused = wr(p, root_ctl, "Shell /nonexistent/zzsh\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "Shell: shell \"/nonexistent/zzsh\" not found") != null);
    try testing.expect(th.logHas(p, "shell \"/nonexistent/zzsh\" not found"));
    try testing.expectEqual(E.IO, wr(p, root_ctl, "Shell /etc\n").errno());
    try testing.expect(th.logHas(p, "Shell: not a shell: /etc is a directory"));
    try testing.expectEqualStrings("", p.settings.shell.requested.get());
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Shell /bin/sh\n").reply.status);
    try testing.expectEqualStrings("/bin/sh", p.settings.shell.requested.get());
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Shell\n").reply.status);
    try testing.expectEqualStrings("", p.settings.shell.requested.get());
    try testing.expect(th.logHas(p, "Shell: the default again, "));
    var want: [300]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, rd(p, root_ctl, 0, 8192).bytes, try std.fmt.bufPrint(&want, "Shell {s}\n", .{config.defaultShell()})) != null);
}

test "a builtin that fails a ctl write logs only its err, so the same failure again is counted" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.tick); // the pane's `new` is logged first
    while (p.nextEffect()) |_| {}
    const ctl_node = @intFromEnum(tree.TopFile.ctl);
    for (0..3) |_| try testing.expectEqual(Status.err, wr(p, ctl_node, "Unmount zzz\n").reply.status);
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    const text = call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes;
    try testing.expect(std.mem.endsWith(u8, text, "err - ctl: Unmount: no such mount zzz (x3)\n"));
    try testing.expect(std.mem.indexOf(u8, text, "msg - Unmount") == null);
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
}

test "an exec line over the command limit fails the write and says the limit; a builtin's may be longer" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const long = "echo " ++ "y" ** pardes.exec.command_max ++ "\n";
    const refused = wr(p, root_exec, long);
    try testing.expectEqual(E.INVAL, refused.errno());
    try testing.expectEqualStrings(e_too_long, refused.reply.ename);
    var rec: [96]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&rec, "err {d} exec: invalid command line: a command line is at most 1024 bytes", .{serialOf(p)})));
    try testing.expectEqualStrings(e_control, wr(p, root_exec, "echo a\x01b\n").reply.ename);
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&rec, "err {d} exec: invalid command line: it holds", .{serialOf(p)})));
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Msg " ++ "z" ** 1100 ++ "\n").reply.status);
}

test "Edit's p and = never fail for want of room for +Errors: the text is logged instead" {
    const p = try withFile(testing.allocator, "one\ntwo\n");
    defer p.deinit();
    p.update(.{ .resize = .{ .cols = 80, .rows = 6 } });
    const ctl_node = Node.of(serialOf(p), .ctl);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Edit ,p\n").reply.status);
    try testing.expect(th.logHas(p, " one\n") and th.logHas(p, " two\n"));
    p.sync();
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    try testing.expectEqual(@as(usize, 1), count); // the +Errors that had no room is gone
}

test "size sets the screen of a session no frontend is attached to, and only of one" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size 120 40\n").errno()); // a frontend's
    p.unattended = true;
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "size 120 40\n").reply.status);
    try testing.expectEqual(@as(u16, 120), p.screen_w);
    try testing.expectEqual(@as(u16, 40), p.screen_h);
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size 120\n").errno());
    try testing.expectEqual(E.INVAL, wr(p, root_ctl, "size\n").errno());
    try testing.expect(std.mem.indexOf(u8, wr(p, root_ctl, "size 5 2\n").reply.ename, "at least 20x6, at most 4096x4096") != null);
    // The bad value quoted, never the word size.
    try testing.expect(std.mem.endsWith(u8, wr(p, root_ctl, "size 5 2\n").reply.ename, "\"5 2\""));
    // Too small for the panes it has, each its tag and two rows: refused,
    // the size as it was.
    for (0..4) |_| p.newScratchBelow(p.active);
    p.sync();
    try testing.expect(std.mem.indexOf(u8, wr(p, root_ctl, "size 80 8\n").reply.ename, "too small for the panes") != null);
    try testing.expectEqual(@as(u16, 40), p.screen_h);
}

test "Mount dials its peer and fails, mounting nothing, when none answers; a look through a peer gone says dial failed" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const dead = "/tmp/pardes-test-no-such-peer.sock";
    const refused = wr(p, root_ctl, "Mount dead " ++ dead ++ "\n");
    try testing.expectEqual(E.IO, refused.errno());
    try testing.expectEqualStrings("Mount dead " ++ dead ++ ": dial failed: no answer", refused.reply.ename);
    try testing.expectEqual(@as(usize, 0), p.fs.mounts.items.len);
    // A pane of a peer gone since: get says so too.
    try p.fs.mounts.append(p.gpa, .{ .name = try p.gpa.dupe(u8, "away"), .dial = try p.gpa.dupe(u8, dead) });
    _ = wr(p, Node.of(serialOf(p), .name), "/n/away/f.txt\n");
    const got = wr(p, Node.of(serialOf(p), .ctl), "get\n");
    try testing.expectEqualStrings("get: /n/away/f.txt: dial failed: no answer", got.reply.ename);
    // Mounted when it answered, gone since: a look through it says so.
    try p.fs.mounts.append(p.gpa, .{ .name = try p.gpa.dupe(u8, "gone"), .dial = try p.gpa.dupe(u8, dead) });
    const looked = wr(p, @intFromEnum(tree.TopFile.look), "/n/gone/f.txt\n");
    try testing.expect(looked.errno() != 0);
    try testing.expect(th.logHas(p, "look: /n/gone/f.txt: dial failed: no answer"));
}

test "a root exec that fails logs its err against the pane it ran at" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const f = &p.panes[0].?.file.?;
    f.saved_revision = f.revision -% 1;
    f.saved_hash = 0;
    try testing.expect(wr(p, root_exec, "Exit\n").errno() != 0);
    var want: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "err {d} exec: ", .{serialOf(p)})));
}

test "Tty in a directory that is not there fails and makes no pane; a shell that never started answers a run" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    _ = wr(p, Node.of(serial, .name), "/tmp/pardes-no-such-dir-zz/f.txt\n");
    // A host that starts shells (the core alone starts none, and asks
    // nothing of a directory).
    const Starting = struct {
        fn spawn(_: ?*anyopaque, _: u8, _: []const u8) void {}
    };
    p.host = .{ .vtable = &.{ .spawn = Starting.spawn } };
    defer p.host = .{};
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const refused = wr(p, Node.of(serial, .ctl), "Tty\n");
    try testing.expectEqual(E.NOENT, refused.errno());
    try testing.expectStringStartsWith(refused.reply.ename, "Tty: /tmp/pardes-no-such-dir-zz: no such directory");
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // A terminal whose shell the host could not start.
    _ = wr(p, Node.of(serial, .name), "/tmp/f.txt\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "Tty\n").reply.status);
    const term = p.active;
    p.shellFailed(@intCast(term), error.FileNotFound);
    const run_node = Node.of(p.panes[term].?.serial, .pty_run);
    const h = call(p, .{ .tag = 1, .op = .open, .node = run_node, .omode = 2 }).reply.handle;
    _ = call(p, .{ .tag = 2, .op = .write, .node = run_node, .handle = h, .data = "true\n" });
    try testing.expectEqualStrings("error shell gone\n", call(p, .{ .tag = 3, .op = .read, .node = run_node, .handle = h, .size = 64 }).bytes);
}

test "a builtin that needs its argument, written bare to an exec, is EINVAL as through ctl" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    for ([_]u64{ root_exec, Node.of(serialOf(p), .exec), @intFromEnum(tree.TopFile.tagexec) }) |node| {
        const refused = wr(p, node, "Mount\n");
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expectEqualStrings("wrong #args in control message \"Mount\"", refused.reply.ename);
    }
}

test "Grep with no hit says grep: no match and opens nothing, a missing pane directory passed over" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = "alpha\n" });
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "other.txt", .data = "one\nbravo here\nthree bravo\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, Node.of(serialOf(p), .name), try std.fmt.bufPrint(&line, "{s}/a.txt\n", .{dir}));
    // A hit opens its +Search, a row a line: exec reads it back. Find and
    // Grep share it, a directory's one +Search, each run replacing it.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .exec), "Grep bravo\n").reply.status);
    const grepped = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?].?;
    try testing.expectEqual(@as(usize, 2), std.mem.count(u8, grepped.file.?.content, "other.txt:"));
    try testing.expect(std.mem.indexOf(u8, grepped.file.?.content, "other.txt:2") != null);
    try testing.expect(std.mem.indexOf(u8, grepped.file.?.content, "other.txt:3") != null);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .exec), "Find other\n").reply.status);
    const found = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?].?;
    try testing.expect(std.mem.indexOf(u8, found.file.?.content, "other.txt") != null);
    try testing.expectEqual(grepped.serial, found.serial);
    try testing.expect(std.mem.indexOf(u8, found.file.?.content, "bravo here") == null);
    // The same Find again reads back the +Search, not the pane it ran in.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .exec), "Find other\n").reply.status);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&line, "{d}\n", .{found.serial}), rd(p, root_exec, 0, 64).bytes);
    // A Grep run from the +Search itself fills that one, never a second.
    try testing.expectEqual(Status.ok, wr(p, Node.of(found.serial, .exec), "Grep bravo\n").reply.status);
    try testing.expectEqualStrings(try std.fmt.bufPrint(&line, "{d}\n", .{found.serial}), rd(p, root_exec, 0, 64).bytes);
    var searches: usize = 0;
    for (p.panes) |slot| if (slot) |q| if (q.file) |f| if (f.output != null) {
        searches += @intFromBool(std.mem.endsWith(u8, f.path, "/+Search"));
    };
    try testing.expectEqual(@as(usize, 1), searches);
    try testing.expect(std.mem.indexOf(u8, found.file.?.content, "bravo here") != null);
    // A second pane in a directory that is not there.
    const other = try th.newPane(p);
    _ = wr(p, Node.of(other, .name), "/tmp/pardes-no-such-dir-zz/b.txt\n");
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const missed = wr(p, Node.of(serialOf(p), .exec), "Grep zzqqnomatchzz\n");
    try testing.expectEqual(E.NOENT, missed.errno());
    try testing.expectEqualStrings("Grep: pattern not found", missed.reply.ename);
    const unfound = wr(p, Node.of(serialOf(p), .exec), "Find zzqqnomatchzz\n");
    try testing.expectEqual(E.NOENT, unfound.errno());
    try testing.expectEqualStrings("Find: name not found", unfound.reply.ename);
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // The +Search the miss would have filled is emptied, not left stale.
    try testing.expectEqualStrings("", found.file.?.content);
}

test "Unmount of a name not mounted says no such mount, which a mount reads as ENOENT" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const refused = wr(p, @intFromEnum(tree.TopFile.ctl), "Unmount nothere\n");
    try testing.expectEqual(E.NOENT, refused.errno());
    try testing.expectStringStartsWith(refused.reply.ename, "Unmount: no such mount nothere");
}

test "a terminal told the directory it already goes by logs no rename" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    _ = wr(p, Node.of(serialOf(p), .name), "/tmp/f.txt\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .ctl), "Tty\n").reply.status);
    p.update(.tick); // announced
    const term = p.active;
    // The host says where its shell started: where it was already named.
    p.setCwd(term, "/tmp");
    var rec: [32]u8 = undefined;
    try testing.expect(!th.logHas(p, try std.fmt.bufPrint(&rec, "rename {d} ", .{p.panes[term].?.serial})));
    // This process's directory, asked before the shell has said anything
    // (so before its chdir): not taken.
    const session = p.sessionDir();
    p.setCwd(term, session);
    try testing.expect(!th.logHas(p, try std.fmt.bufPrint(&rec, "rename {d} ", .{p.panes[term].?.serial})));
    p.update(.{ .output = .{ .pane = @intCast(term), .bytes = "$ " } });
    // Somewhere else is a rename.
    p.setCwd(term, "/usr");
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&rec, "rename {d} /usr", .{p.panes[term].?.serial})));
}

test "a terminal with text typed at its prompt is never typed into: a look at its directory opens another" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const term = p.paneBySerial(serialOf(p)).?;
    p.setCwd(term, "/tmp");
    p.update(.{ .output = .{ .pane = @intCast(term), .bytes = "\x1b]133;A;aid=pardes\x07$ \x1b]133;B;aid=pardes\x07TYPED" } });
    while (p.nextEffect()) |_| {}
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.look), "/tmp\n").reply.status);
    var typed_into = false;
    while (p.nextEffect()) |effect| if (effect == .write and effect.write.pane == term) {
        typed_into = true;
    };
    try testing.expect(!typed_into);
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count + 1, after);
    // An exec at it runs in a pane of its own, not typed after TYPED.
    _ = wr(p, Node.of(serialOf(p), .exec), "echo hi\n");
    while (p.nextEffect()) |effect| if (effect == .write and effect.write.pane == term) {
        typed_into = true;
    };
    try testing.expect(!typed_into);
}

test "a command line from a missing directory fails ENOENT and makes no pane; a command whose shell never started ends 127" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const Starting = struct {
        fn spawn(_: ?*anyopaque, _: u8, _: []const u8) void {}
    };
    p.host = .{ .vtable = &.{ .spawn = Starting.spawn } };
    defer p.host = .{};
    const serial = serialOf(p);
    _ = wr(p, Node.of(serial, .name), "/tmp/pardes-no-such-dir-zz/f.txt\n");
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const refused = wr(p, Node.of(serial, .exec), "echo hi\n");
    try testing.expectEqual(E.NOENT, refused.errno());
    try testing.expectStringStartsWith(refused.reply.ename, "exec: /tmp/pardes-no-such-dir-zz: no such directory");
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // A command pane whose shell the host could not start.
    _ = wr(p, Node.of(serial, .name), "/tmp/f.txt\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "echo hi\n").reply.status);
    const cmd = p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, Node.of(serial, .exec), 0, 64).bytes, "\n"), 10)).?;
    p.shellFailed(@intCast(cmd), error.FileNotFound);
    const pane = p.panes[cmd].?;
    try testing.expect(pane.command_done);
    try testing.expectEqual(@as(?u8, 127), pane.command_status);
    var rec: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&rec, "exit {d} 127\n", .{pane.serial})));
    try testing.expect(th.logHas(p, "shell: directory missing"));
}

test "pty/ctl exec in a directory that is gone fails ENOENT; a shell that cannot start fails the write" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const Starting = struct {
        fn spawn(_: ?*anyopaque, _: u8, _: []const u8) void {}
    };
    p.host = .{ .vtable = &.{ .spawn = Starting.spawn } };
    defer p.host = .{};
    const serial = serialOf(p);
    p.setCwd(p.paneBySerial(serial).?, "/tmp/pardes-no-such-dir-zz");
    const refused = wr(p, Node.of(serial, .pty_ctl), "exec\n");
    try testing.expectEqual(E.NOENT, refused.errno());
    try testing.expectStringStartsWith(refused.reply.ename, "exec: /tmp/pardes-no-such-dir-zz: no such directory");
    // The host's own failure is the waiting write's (late_failure).
    p.fs.late_failure_len = 0;
    p.shellFailed(@intCast(p.paneBySerial(serial).?), error.AccessDenied);
    try testing.expectEqualStrings("shell: access denied", p.fs.late_failure[0..p.fs.late_failure_len]);
}

test "a script whose interpreter is not there: Tty refuses it up front, only an err logged, and pty/ctl exec keeps the running shell" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const Starting = struct {
        fn spawn(_: ?*anyopaque, _: u8, _: []const u8) void {}
    };
    p.host = .{ .vtable = &.{ .spawn = Starting.spawn } };
    defer p.host = .{};
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "bad", .data = "#!/no/such/interp\n", .flags = .{ .permissions = .executable_file } });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const serial = serialOf(p);
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const refused = wr(p, Node.of(serial, .ctl), try std.fmt.bufPrint(&line, "Tty {s}/bad\n", .{dir}));
    try testing.expectEqual(E.NOENT, refused.errno());
    try testing.expectEqualStrings("Tty: interpreter /no/such/interp not found", refused.reply.ename);
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // The log gained the err and nothing else: no new, msg or del.
    try testing.expect(th.logHas(p, "Tty: interpreter /no/such/interp not found\n"));
    try testing.expect(!th.logHas(p, "\nmsg "));
    try testing.expect(!th.logHas(p, "\ndel "));
    // The shell to start again is that script: refused before the running
    // one goes.
    const id = p.paneBySerial(serial).?;
    p.panes[id].?.shell = try p.gpa.dupe(u8, try std.fmt.bufPrint(&line, "{s}/bad", .{dir}));
    p.setCwd(id, dir);
    const exec_refused = wr(p, Node.of(serial, .pty_ctl), "exec\n");
    try testing.expectEqual(E.NOENT, exec_refused.errno());
    try testing.expectEqualStrings("exec: interpreter /no/such/interp not found", exec_refused.reply.ename);
    // One the host found could not start (the script changed after): said
    // with the interpreter's name, and the running shell is not gone.
    p.fs.late_failure_len = 0;
    p.restartFailed(@intCast(id), error.InterpreterNotFound);
    try testing.expectEqualStrings("shell: interpreter /no/such/interp not found", p.fs.late_failure[0..p.fs.late_failure_len]);
    try testing.expect(!p.panes[id].?.shell_failed);
}

test "a language server question that finds nothing, cannot be answered, or is asked of no file fails, and a write to an image's body is refused" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const id = p.active;
    // Asked of a pane that is no file's: at once.
    _ = wr(p, root_exec, "Recent\n");
    const listed = p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?;
    p.lspRequest(listed, .incoming_calls, "");
    try testing.expect(std.mem.indexOf(u8, p.panes[listed].?.msg[0..p.panes[listed].?.msg_len], "Callers: only a file's pane asks") != null);
    // Nothing found: Callers says so, and the waiting write hears it.
    p.fs.late_failure_len = 0;
    p.lspRequest(id, .incoming_calls, "");
    try testing.expect(p.lsp_wait != null);
    p.lspResponse(p.lsp_wait.?.id, "");
    try testing.expectEqualStrings("Callers: callers not found", p.fs.late_failure[0..p.fs.late_failure_len]);
    // A backend that cannot answer says why.
    p.fs.late_failure_len = 0;
    p.lspRequest(id, .outgoing_calls, "");
    p.lspResponse(p.lsp_wait.?.id, "@none zls does not answer call hierarchy\n");
    try testing.expectEqualStrings("Callees: zls does not answer call hierarchy", p.fs.late_failure[0..p.fs.late_failure_len]);
    // No answer at all.
    p.fs.late_failure_len = 0;
    p.lspRequest(id, .hover, "");
    p.lspResponse(p.lsp_wait.?.id, null);
    try testing.expectEqualStrings("Hover: the language server did not answer", p.fs.late_failure[0..p.fs.late_failure_len]);
    // No diagnostics is no failure.
    p.fs.late_failure_len = 0;
    p.lspRequest(id, .diagnostics, "");
    p.lspResponse(p.lsp_wait.?.id, "");
    try testing.expectEqual(@as(u16, 0), p.fs.late_failure_len);
    // An image's body takes no write.
    const slot = p.freeSlot().?;
    const img = try pardes.panes.Image.create(p, slot, "/tmp/pardes-no-such.png", try p.image_gpa.dupe(u8, "not a png"));
    try testing.expectEqual(E.INVAL, wr(p, Node.of(img.serial, .body), "text\n").errno());
}

test "a corrupt image fails its look with an err, and no pane is made" {
    pardes.image.start(testing.io, testing.allocator);
    defer pardes.image.stop();
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "bad.png", .data = "\x89PNG not really" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    const r = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/bad.png\n", .{dir}));
    try testing.expectEqual(E.IO, r.errno());
    try testing.expect(std.mem.endsWith(u8, r.reply.ename, "bad.png: not an image pardes can read"));
    p.sync();
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
}

test "a truncated PDF fails its look with its path and why" {
    if (comptime !pardes.pdf_enabled) return;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    const bytes = try @import("mupdf").makeLinksTestPdf(testing.allocator);
    defer testing.allocator.free(bytes);
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "cut.pdf", .data = bytes[0..40] });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const r = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/cut.pdf\n", .{dir}));
    try testing.expectEqual(Status.err, r.reply.status);
    try testing.expect(std.mem.indexOf(u8, r.reply.ename, "cut.pdf: not a PDF pardes can read: ") != null);
}

test "a PDF's body reads its page's text layer, and takes no write" {
    if (comptime !pardes.pdf_enabled) return;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    const bytes = try @import("mupdf").makeLinksTestPdf(testing.allocator);
    defer testing.allocator.free(bytes);
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "doc.pdf", .data = bytes });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/doc.pdf\n", .{dir}));
    p.sync();
    const doc = p.panes[p.active].?;
    try testing.expect(doc.hasPdf());
    const body = Node.of(doc.serial, .body);
    try testing.expect(std.mem.indexOf(u8, rd(p, body, 0, 4096).bytes, "target.txt") != null);
    try testing.expectEqual(E.INVAL, wr(p, body, "more\n").errno());
}

test "Grep, Symbols and Diagnostics share their directory's one +Search" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const id = p.active;
    const Output = pardes.panes.Output;
    try Output.fillResults(p, id, "/tmp", .{ .cmd = .Grep }, "x", try p.gpa.dupe(u8, "a.txt:1:1 x\n"), null);
    try Output.fillResults(p, id, "/tmp", .{ .query = .document_symbols }, "", try p.gpa.dupe(u8, "a.txt:2:1 fn f\n"), null);
    try Output.fillResults(p, id, "/tmp", .{ .query = .diagnostics }, "", try p.gpa.dupe(u8, "a.txt:3:1 error\n"), null);
    var searches: usize = 0;
    for (p.panes) |slot| if (slot) |q| if (q.file) |f| if (f.output != null) {
        searches += @intFromBool(std.mem.eql(u8, f.path, "/tmp/+Search"));
    };
    try testing.expectEqual(@as(usize, 1), searches);
}

test "+Unsaved drops a pane once it has closed" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const a = try th.newPane(p);
    _ = wr(p, Node.of(a, .name), "/tmp/pardes-unsaved-a.txt\n");
    _ = wr(p, Node.of(a, .body), "edited\n");
    const b = try th.newPane(p);
    _ = wr(p, Node.of(b, .name), "/tmp/pardes-unsaved-b.txt\n");
    _ = wr(p, Node.of(b, .body), "edited\n");
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    try testing.expectEqual(Status.err, wr(p, root_ctl, "Exit\n").reply.status);
    var listed: ?*pardes.Pane = null;
    for (p.panes) |slot| if (slot) |q| if (q.file) |f| if (f.output) |o| if (o.from == .unsaved) {
        listed = q;
    };
    const list = listed.?;
    try testing.expect(std.mem.indexOf(u8, list.file.?.content, "/tmp/pardes-unsaved-a.txt: Modified") != null);
    // a closes (discarded): its row goes; b's stays.
    _ = wr(p, Node.of(a, .ctl), "Del\n");
    _ = wr(p, Node.of(a, .ctl), "Del\n");
    p.sync();
    try testing.expect(p.paneBySerial(a) == null);
    try testing.expect(std.mem.indexOf(u8, list.file.?.content, "/tmp/pardes-unsaved-a.txt: Modified") == null);
}

test "a buffer whose file was deleted on disk is dirty, and Del asks first" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    try testing.expectEqualStrings("0", std.mem.trimEnd(u8, rd(p, Node.of(serial, .dirty), 0, 8).bytes, "\n"));
    pardes.panes.File.deleted(p, @intCast(p.paneBySerial(serial).?));
    try testing.expectEqualStrings("1", std.mem.trimEnd(u8, rd(p, Node.of(serial, .dirty), 0, 8).bytes, "\n"));
    try testing.expectEqual(Status.err, wr(p, Node.of(serial, .ctl), "Del\n").reply.status);
    try testing.expect(p.paneBySerial(serial) != null);
    _ = wr(p, Node.of(serial, .ctl), "Del\n");
    p.sync();
    try testing.expect(p.paneBySerial(serial) == null);
}

test "a failure said while a 9P write waits on it posts no msg, only the write's err" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.fs.write_waits = true;
    p.saveFailed(@intCast(p.active), "/nowhere/zz.txt", error.FileNotFound);
    p.fs.write_waits = false;
    try testing.expect(!th.logHas(p, "msg "));
    try testing.expect(p.fs.late_failure_len > 0);
}

test "Mini with no argument is wrong #args, EINVAL, as every word that needs one" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const r = wr(p, Node.of(serialOf(p), .ctl), "Mini\n");
    try testing.expectEqual(E.INVAL, r.errno());
    try testing.expectEqualStrings("wrong #args in control message \"Mini\"", r.reply.ename);
}

test "a look that misses file:/re/ names the file, and is logged as its pane's" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "alpha\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/f.txt\n", .{dir}));
    p.sync();
    const f_serial = p.panes[p.active].?.serial;
    _ = wr(p, Node.of(serialOf(p), .look), try std.fmt.bufPrint(&line, "{s}/f.txt:/zzqq/\n", .{dir}));
    var want: [4300]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "err {d} look: {s}/f.txt: no match for regexp", .{ f_serial, dir })));
}

test "with no pane at all, the root look opens its file and the root exec runs in the session's directory" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "file\n" });
    var buf: [4096]u8 = undefined;
    const session = buf[0..try tmp.dir.realPath(testing.io, &buf)];
    @memcpy(p.session_dir[0..session.len], session);
    p.session_dir_len = @intCast(session.len);
    const Empty = struct {
        fn all(q: *Pardes) !void {
            while (q.anyPane()) |k| _ = wr(q, Node.of(q.panes[k].?.serial, .ctl), "delete\n");
        }
    };
    try Empty.all(p);
    const look_node = @intFromEnum(tree.TopFile.look);
    try testing.expectEqual(Status.ok, wr(p, look_node, "f.txt\n").reply.status);
    var want: [4200]u8 = undefined;
    const path = try std.fmt.bufPrint(&want, "{s}/f.txt", .{session});
    var opened: usize = 0;
    var scratches: usize = 0;
    for (p.panes) |slot| {
        const f = (slot orelse continue).file orelse continue;
        opened += @intFromBool(std.mem.eql(u8, f.path, path));
        scratches += @intFromBool(std.mem.endsWith(u8, f.path, "/+New"));
    }
    try testing.expectEqual(@as(usize, 1), opened);
    try testing.expectEqual(@as(usize, 0), scratches);

    try Empty.all(p);
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.exec), "echo hi\n").reply.status);
    const made = p.panes[p.anyPane().?].?;
    try testing.expect(made.command != null);
    try testing.expectEqualStrings(session, made.cwdSlice());
}

test "a look at file:3:0 is refused as addr 3:0 is, a column counting from 1" {
    const p = try withFile(testing.allocator, "one\ntwo\nthree\n");
    defer p.deinit();
    const serial = serialOf(p);
    const by_addr = wr(p, Node.of(serial, .addr), "3:0");
    const by_look = wr(p, Node.of(serial, .look), "/test.txt:3:0\n");
    try testing.expectEqual(E.INVAL, by_addr.errno());
    try testing.expectEqual(E.INVAL, by_look.errno());
    try testing.expectEqualStrings(by_addr.reply.ename, by_look.reply.ename);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), "/test.txt:3:1\n").reply.status);
}

test "Kill with a name and nothing running says so and does not fail, as bare Kill does" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const r = wr(p, @intFromEnum(tree.TopFile.ctl), "Kill zzz\n");
    try testing.expectEqual(Status.ok, r.reply.status);
    try testing.expect(th.logHas(p, "Kill: nothing running"));
}

test "a restored pane whose file is gone from disk comes back dirty, and Del asks first" {
    if (comptime !pardes.hosted) return error.SkipZigTest;
    const p = try withFile(testing.allocator, "kept text\n");
    defer p.deinit();
    // On disk when dumped, gone by the Restore.
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "kept text\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var path_buf: [4200]u8 = undefined;
    try pane_files.nameBuffer(p, 0, try std.fmt.bufPrint(&path_buf, "{s}/f.txt", .{dir}), false);
    try pardes.dump.dumpState(p);
    try tmp.dir.deleteFile(testing.io, "f.txt");
    const restored = try pardes.dump.restore(p, p.dump_out.?, "/tmp/pardes.dump.zon");
    defer restored.deinit();
    const again = restored.panes[restored.paneBySerial(restored.panes[0].?.serial).?].?;
    try testing.expect(again.file.?.disk_gone);
    const r = wr(restored, Node.of(again.serial, .ctl), "Del\n");
    try testing.expectEqual(Status.err, r.reply.status);
    try testing.expect(std.mem.indexOf(u8, r.reply.ename, "Modified") != null);
}

test "a 9P look keeps its leading blanks, a blank-only look included, and exec still trims" {
    const p = try withFile(testing.allocator, "a indented\nb\n    indented\n    \n");
    defer p.deinit();
    const serial = serialOf(p);
    const pane = p.panes[p.paneBySerial(serial).?].?;
    pane_files.setDot(pane, .{ .q0 = 0, .q1 = 0 });
    // The indented line, not the `indented` after `a `.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), "    indented\n").reply.status);
    try testing.expectEqual(pane_files.State.Range{ .q0 = 13, .q1 = 25 }, pane_files.dotOf(pane));
    // Blanks alone are text to find too.
    pane_files.setDot(pane, .{ .q0 = 26, .q1 = 26 });
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), "    \n").reply.status);
    try testing.expectEqual(pane_files.State.Range{ .q0 = 26, .q1 = 30 }, pane_files.dotOf(pane));
    // exec's line is still trimmed: `  Msg hi` runs Msg.
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "  Msg blanks trimmed\n").reply.status);
    try testing.expect(th.logHas(p, "blanks trimmed"));
}

test "a focus moved over 9P tells the programs that asked for focus reports, as a click does" {
    const p = try Pardes.init(testing.allocator, .{ .cols = 90, .rows = 30, .shells = 2 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const first = for (p.panes) |slot| {
        if (slot) |pane| if (pane.isTerminal()) break pane.serial;
    } else return error.NoShell;
    try testing.expectEqual(Status.ok, wr(p, Node.of(first, .exec), "Tty\n").reply.status);
    var shells: [2]usize = undefined;
    var n: usize = 0;
    for (p.panes, 0..) |slot, id| if (slot) |pane| if (pane.isTerminal() and n < 2) {
        shells[n] = id;
        n += 1;
    };
    try testing.expectEqual(@as(usize, 2), n);
    p.active = shells[0];
    p.update(.{ .output = .{ .pane = @intCast(shells[0]), .bytes = "\x1b[?1004h" } });
    p.update(.{ .output = .{ .pane = @intCast(shells[1]), .bytes = "\x1b[?1004h" } });
    while (p.nextEffect()) |_| {}
    var digits: [16]u8 = undefined;
    const moved = wr(p, @intFromEnum(tree.TopFile.focus), try std.fmt.bufPrint(&digits, "{d}\n", .{p.panes[shells[1]].?.serial}));
    try testing.expectEqual(Status.ok, moved.reply.status);
    try testing.expectEqual(shells[1], p.active);
    try testing.expectEqualStrings("\x1b[O\x1b[I", moved.pty_buf[0..moved.pty_len]);
}

test "a Restore of a name in the DumpDir asks for, and logs, the whole path it reads" {
    if (comptime !pardes.hosted) return error.SkipZigTest;
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    try pardes.dump.dumpState(p);
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "x.dump.zon", .data = p.dump_out.? });
    var buf: [4096]u8 = undefined;
    const dir = buf[0..try tmp.dir.realPath(testing.io, &buf)];
    try testing.expect(p.settings.dump_dir.set(dir));
    try testing.expectEqual(Status.ok, wr(p, @intFromEnum(tree.TopFile.ctl), "Restore x.dump.zon\n").reply.status);
    var want: [4200]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "{s}/x.dump.zon", .{dir}), p.restore_req.?);
}

test "a line starting with # runs as nothing at an exec or a ctl, silently" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    // The setup's own announcements are made by the first write's update.
    _ = wr(p, @intFromEnum(tree.TopFile.ctl), "# settle\n");
    const before = p.next_serial;
    const log_before = try pardes.ctlfs.events.freezeLog(p);
    defer p.gpa.free(log_before.bytes);
    for ([_]u64{ @intFromEnum(tree.TopFile.exec), Node.of(serial, .exec), @intFromEnum(tree.TopFile.ctl), Node.of(serial, .ctl), Node.ofCol(layout.columnSerial(p, 0), .ctl) }) |node| {
        try testing.expectEqual(Status.ok, wr(p, node, "# Platform: tty\n  # indented too\n").reply.status);
    }
    try testing.expectEqual(before, p.next_serial);
    const log_after = try pardes.ctlfs.events.freezeLog(p);
    defer p.gpa.free(log_after.bytes);
    try testing.expectEqualStrings(log_before.bytes, log_after.bytes);
}

test "the ctl word name refuses a leading blank, as the name file does" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    const r = wr(p, Node.of(serial, .ctl), "name  /tmp/lead.txt\n");
    try testing.expectEqual(E.INVAL, r.errno());
    try testing.expectEqualStrings("bad character in file name: a blank at its start", r.reply.ename);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .ctl), "name /tmp/ok.txt\n").reply.status);
    try testing.expectEqualStrings("/tmp/ok.txt", pane_files.nameOf(p, p.panes[0].?));
}

test "a builtin that takes no argument, written with one to an exec, is refused wrong #args, as at a ctl" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    for ([_]u64{ @intFromEnum(tree.TopFile.exec), Node.of(serial, .exec) }) |node| for ([_][]const u8{ "Config extra\n", "DumpConfig extra\n" }) |line| {
        const r = wr(p, node, line);
        try testing.expectEqual(E.INVAL, r.errno());
        try testing.expectStringStartsWith(r.reply.ename, "wrong #args in control message");
    };
}

test "acme's words run as pardes's (Put is Save, Delete a Del that does not ask) or are refused, never run as commands" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    for ([_][]const u8{ "Snarf\n", "Putall\n", "Zerox\n", "Get\n", "Tab\n", "Indent\n", "Local\n", "Incl\n", "Abort\n" }) |line| {
        for ([_]u64{ Node.of(serial, .ctl), Node.of(serial, .exec) }) |node| {
            const r = wr(p, node, line);
            try testing.expectEqual(E.INVAL, r.errno());
            try testing.expect(std.mem.indexOf(u8, r.reply.ename, "is not a pardes builtin") != null);
        }
    }
    // Put saves, as Save does.
    _ = wr(p, Node.of(serial, .name), "/tmp/pardes-put.txt\n");
    const put = wr(p, Node.of(serial, .exec), "Put\n");
    try testing.expectEqual(Status.ok, put.reply.status);
    try testing.expect(put.saved);
    // Delete closes an edited pane without asking.
    const made = try th.newPane(p);
    _ = wr(p, Node.of(made, .name), "/tmp/pardes-delete.txt\n");
    _ = wr(p, Node.of(made, .body), "edited\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(made, .ctl), "Delete\n").reply.status);
    p.sync();
    try testing.expect(p.paneBySerial(made) == null);
}

test "a pane's ctl takes acme's words: done by the files that replace them, or refused with why" {
    const p = try withFile(testing.allocator, "one two\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const pane = p.panes[p.paneBySerial(serial).?].?;
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "name /tmp/pardes-acme-ctl.txt\n").reply.status);
    try testing.expectEqualStrings("/tmp/pardes-acme-ctl.txt", pane.file.?.path);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "dirty\n").reply.status);
    try testing.expectEqualStrings("1", std.mem.trimEnd(u8, rd(p, Node.of(serial, .dirty), 0, 8).bytes, "\n"));
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "clean\n").reply.status);
    try testing.expectEqualStrings("0", std.mem.trimEnd(u8, rd(p, Node.of(serial, .dirty), 0, 8).bytes, "\n"));
    _ = wr(p, Node.of(serial, .addr), "/two/");
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "dot=addr\nshow\nnomark\nmark\nlimit=addr\n").reply.status);
    try testing.expectEqual(@as(u32, 4), pane_files.dotOf(pane).q0);
    try testing.expect(pane.fs.limit != null);
    try testing.expectEqual(Status.ok, wr(p, ctl_node, "cleartag\n").reply.status);
    for ([_][]const u8{ "menu", "nomenu", "dump echo hi", "dumpdir /tmp", "font Go Mono" }) |line| {
        const r = wr(p, ctl_node, line);
        try testing.expectEqual(E.INVAL, r.errno());
        try testing.expect(std.mem.startsWith(u8, r.reply.ename, "invalid: acme's "));
    }
    // Checked whole: a refused word anywhere and nothing ran.
    try testing.expectEqual(E.INVAL, wr(p, ctl_node, "dirty\nmenu\n").errno());
    try testing.expectEqualStrings("0", std.mem.trimEnd(u8, rd(p, Node.of(serial, .dirty), 0, 8).bytes, "\n"));
}

test "ctl reads acme's fields in acme's order, undo and redo flags included, then pardes's own" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const ctl_node = Node.of(serial, .ctl);
    const fields = struct {
        fn of(text: []const u8, buf: *[16][]const u8) [][]const u8 {
            var it = std.mem.tokenizeScalar(u8, text, ' ');
            var n: usize = 0;
            while (it.next()) |t| : (n += 1) buf[n] = t;
            return buf[0..n];
        }
    };
    var buf: [16][]const u8 = undefined;
    var f = fields.of(rd(p, ctl_node, 0, 4096).bytes, &buf);
    try testing.expectEqualStrings("0", f[8]); // nothing to undo
    try testing.expectEqualStrings("0", f[9]); // nothing to redo
    try testing.expect(std.mem.eql(u8, f[10], "current") or std.mem.eql(u8, f[10], "notcurrent"));
    _ = wr(p, Node.of(serial, .body), "two\n");
    f = fields.of(rd(p, ctl_node, 0, 4096).bytes, &buf);
    try testing.expectEqualStrings("1", f[8]);
    _ = wr(p, ctl_node, "Undo\n");
    f = fields.of(rd(p, ctl_node, 0, 4096).bytes, &buf);
    try testing.expectEqualStrings("1", f[9]);
}

test "a write to addr, limit or mark asks for no frame; one to body does" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    for ([_]tree.PaneFile{ .addr, .limit, .mark }) |file| {
        p.needs_frame = false;
        _ = p.serveFs(.{ .tag = 1, .op = .write, .node = Node.of(serial, file), .data = if (file == .mark) "1" else "#0" });
        try testing.expect(!p.needs_frame);
    }
    p.needs_frame = false;
    _ = p.serveFs(.{ .tag = 1, .op = .write, .node = Node.of(serial, .body), .data = "two\n" });
    try testing.expect(p.needs_frame);
}

test "every EINVAL a write gets says why, in its err record too; DEL is a control character in a line" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log, .omode = 2 }).reply.handle;
    const Case = struct { node: u64, data: []const u8, words: []const u8, handle: u32 = 0 };
    for ([_]Case{
        .{ .node = root_exec, .data = "echo a\x7fb\n", .words = "control character" },
        .{ .node = root_look, .data = "a\x7fb\n", .words = "control character" },
        .{ .node = Node.of(serial, .name), .data = "\n", .words = "an empty name" },
        .{ .node = log, .data = "bogus\n", .words = "takes `follow`", .handle = h },
    }) |c| {
        const refused = call(p, .{ .tag = 2, .op = .write, .node = c.node, .handle = c.handle, .data = c.data });
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expect(std.mem.indexOf(u8, refused.reply.ename, c.words) != null);
    }
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
    try testing.expect(!th.logHas(p, "Invalid argument"));
    try testing.expect(th.logHas(p, "an empty name"));
}

test "/index shows a name as the log does: a newline in it is \\n, a control byte, C1 or byte not UTF-8 \\xNN" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const term = p.paneBySerial(serialOf(p)).?;
    p.setCwd(term, "/tmp/two\nlines\x07\x7f\xc2\x85\xff");
    const index = rd(p, @intFromEnum(tree.TopFile.index), 0, 4096).bytes;
    // Each byte as itself, so the name decodes to what it is.
    try testing.expect(std.mem.indexOf(u8, index, "/tmp/two\\nlines\\x07\\x7f\\xc2\\x85\\xff ") != null);
    try testing.expectEqual(@as(usize, 1), std.mem.count(u8, index, "\n"));
    try testing.expect(index.len > 0);
    try testing.expectEqual(@as(u64, 0), call(p, .{ .tag = 1, .op = .getattr, .node = @intFromEnum(tree.TopFile.index) }).reply.attr.size);
    // Its tag never carries the raw newline either.
    const tag = rd(p, Node.of(serialOf(p), .tag), 0, 4096).bytes;
    try testing.expect(std.mem.indexOf(u8, tag, "/tmp/two\\nlines") != null);
    // A backslash of the name's own is doubled: `\n` written in a name
    // reads back unlike a newline.
    p.setCwd(term, "/tmp/back\\nslash");
    try testing.expect(std.mem.indexOf(u8, rd(p, @intFromEnum(tree.TopFile.index), 0, 4096).bytes, "/tmp/back\\\\nslash") != null);
}

test "a look at a ./ or ../ name that is not there names the file, ENOENT; a plain one is looked for as text" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.createDirPath(testing.io, "many");
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, Node.of(serialOf(p), .name), try std.fmt.bufPrint(&line, "{s}/many/a.txt\n", .{dir}));
    for ([_][]const u8{ "./zz.txt", "../zz.txt" }) |name| {
        const r = wr(p, Node.of(serialOf(p), .look), try std.fmt.bufPrint(&line, "{s}\n", .{name}));
        try testing.expectEqual(E.NOENT, r.errno());
        var want: [64]u8 = undefined;
        try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "look: {s}: no such file", .{name}), r.reply.ename);
    }
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .look), "zz.txt\n").reply.status);
    try testing.expect(th.logHas(p, "look: no match for \"zz.txt\""));
}

test "a served-tree pane spoils no Grep, and Look . from a gone directory is ENOENT, not /virtual/" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "hit.txt", .data = "needle here\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, Node.of(serialOf(p), .name), try std.fmt.bufPrint(&line, "{s}/other.txt\n", .{dir}));
    // A pane of the served tree.
    const virtual = try th.newPane(p);
    _ = wr(p, Node.of(virtual, .name), "/virtual/index\n");
    // One named the served tree's root, whose directory is `/`.
    const top = try th.newPane(p);
    _ = wr(p, Node.of(top, .name), "/virtual\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .exec), "Grep needle\n").reply.status);
    // `.` from a pane whose directory is gone.
    const gone = try th.newPane(p);
    _ = wr(p, Node.of(gone, .name), "/tmp/pardes-no-such-dir-zz/f.txt\n");
    const looked = wr(p, Node.of(gone, .look), ".\n");
    try testing.expectEqual(E.NOENT, looked.errno());
    try testing.expectStringStartsWith(looked.reply.ename, "look: /tmp/pardes-no-such-dir-zz: no such directory");
}

test "a tag write refuses NUL and the other control characters" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    for ([_]u64{ @intFromEnum(tree.TopFile.tag), tree.Node.ofCol(pardes.layout.columnSerial(p, 0), .tag), Node.of(serialOf(p), .tag) }) |node| {
        const refused = wr(p, node, " a\x00b");
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expectStringStartsWith(refused.reply.ename, "invalid tag text");
        try testing.expectEqual(E.INVAL, wr(p, node, " \x7f").errno());
    }
}

test "a malformed address is bad address syntax; on a pane with no text any address is refused as nothing to address" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const t = try withFile(testing.allocator, "one\n");
    defer t.deinit();
    for ([_][]const u8{ "1x", "/(/", ",,x" }) |expr| {
        const refused = wr(t, Node.of(serialOf(t), .addr), expr);
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expect(refused.reply.ename.len > 0);
    }
    try testing.expectEqualStrings("bad address syntax", wr(t, Node.of(serialOf(t), .addr), "1x").reply.ename);
    // A terminal (as an image or a PDF): addr, dot and limit alike.
    for ([_]tree.PaneFile{ .addr, .dot, .limit }) |file| for ([_][]const u8{ "1", "1x" }) |expr| {
        const refused = wr(p, Node.of(serialOf(p), file), expr);
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expectEqualStrings("invalid address: this pane has no text to address", refused.reply.ename);
    };
}

test "a bad event record says what is wrong with it" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const event = Node.of(serialOf(p), .event);
    const h = call(p, .{ .tag = 1, .op = .open, .node = event, .omode = 2 }).reply.handle;
    for ([_][2][]const u8{
        .{ "MI0 1 0 1 x\n", "only a look or exec" },
        .{ "MX3 1 0 0 \n", "ends before it starts" },
        .{ "MX9 9 0 0 \n", "range past end" },
        .{ "garbage\n", "a record is" },
    }) |c| {
        const refused = call(p, .{ .tag = 2, .op = .write, .node = event, .handle = h, .data = c[0] });
        try testing.expectEqual(E.INVAL, refused.errno());
        try testing.expect(std.mem.indexOf(u8, refused.reply.ename, c[1]) != null);
    }
    _ = call(p, .{ .tag = 3, .op = .release, .node = event, .handle = h });
}

test "a column takes panes until their documented minimums fill it, not until none can be halved" {
    const p = try Pardes.init(testing.allocator, .{ .tty_only = true, .cols = 160, .rows = 50 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const new = @intFromEnum(tree.TopFile.new);
    while (call(p, .{ .tag = 1, .op = .open, .node = new }).reply.status == .ok) p.sync();
    p.sync();
    const avail = p.screen_h - (p.topBarHeight() + p.columnBarHeight());
    for (0..p.ncol) |c| {
        var need: u32 = 0;
        for (p.col_panes[c][0..p.col_n[c]]) |k| need += layout.minRows(p, k);
        // Refused only when one more pane's tag and two rows would not fit.
        if (p.col_n[c] > 1) try testing.expect(avail - need < 3);
        // Every pane keeps its minimum.
        for (p.col_panes[c][0..p.col_n[c]]) |k| try testing.expect(p.rects[k].h >= layout.minRows(p, k));
    }
}

test "Jumplist fills its one +Jumps again, as Recent does, never a second" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    var count: [2]usize = undefined;
    for (&count) |*n| {
        try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .exec), "Jumplist\n").reply.status);
        p.sync();
        n.* = 0;
        for (p.panes) |slot| if (slot) |pane| if (pane.file) |f| if (f.output) |o| {
            n.* += @intFromBool(std.meta.eql(o.from, panes.Output.Origin{ .cmd = .Jumplist }));
        };
    }
    try testing.expectEqual(@as(usize, 1), count[0]);
    try testing.expectEqual(@as(usize, 1), count[1]);
}

test "a Jumplist entry is (closed) only while no pane has its file open" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = "one\n" });
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "b.txt", .data = "two\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt\n", .{dir}));
    p.sync();
    const a = p.panes[p.active].?.serial;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/b.txt\n", .{dir}));
    p.sync();
    _ = wr(p, Node.of(a, .ctl), "Del\n");
    p.sync();
    var closed: usize = 0;
    for (p.jumps[0..p.njumps]) |j| closed += @intFromBool(j.serial == 0);
    try testing.expect(closed > 0);
    // Open again, by a look: no entry is closed any more.
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt\n", .{dir}));
    p.sync();
    for (p.jumps[0..p.njumps]) |j| try testing.expect(j.serial != 0);
}

test "Recent's row for a file still open is where its dot is now, not where it last closed" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = "one\ntwo\nthree\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt:3\n", .{dir})).reply.status);
    p.sync();
    const pane = p.panes[p.active].?;
    pane.body.vsel.active = false; // the look's selection of line 3 let go
    pane.body.cur_row = 1;
    pane.body.cur_col = 2;
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Recent\n").reply.status);
    const rows = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?].?;
    var want: [4300]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, rows.file.?.content, try std.fmt.bufPrint(&want, "{s}/a.txt:2:3 open\n", .{dir})) != null);
}

test "a closed file is found again: Recent and /recent list it closed, a look at its row reopens it at its dot, and a jump back does too" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = "one\ntwo\nthree\n" });
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "b.txt", .data = "bee\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const a_path = try std.fmt.bufPrint(&line, "{s}/a.txt", .{dir});
    var a_buf: [4200]u8 = undefined;
    const a = a_buf[0..a_path.len];
    @memcpy(a, a_path);
    // Opened, its dot on line 3, then closed.
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&line, "{s}:3\n", .{a})).reply.status);
    p.sync();
    const opened = p.active;
    try testing.expectEqualStrings(a, p.panes[opened].?.file.?.path);
    var want: [4300]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, rd(p, @intFromEnum(tree.TopFile.recent), 0, 8192).bytes, try std.fmt.bufPrint(&want, "open {s}\n", .{a})) != null);
    // Another file, so the jumplist has somewhere to come back from.
    try testing.expectEqual(Status.ok, wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/b.txt\n", .{dir})).reply.status);
    p.sync();
    try testing.expectEqual(Status.ok, wr(p, Node.of(p.panes[opened].?.serial, .ctl), "Del\n").reply.status);
    p.sync();
    try testing.expect(std.mem.indexOf(u8, rd(p, @intFromEnum(tree.TopFile.recent), 0, 8192).bytes, try std.fmt.bufPrint(&want, "closed {s}\n", .{a})) != null);
    // Recent lists it, closed, at its dot; a look at the row opens it there.
    try testing.expectEqual(Status.ok, wr(p, root_exec, "Recent\n").reply.status);
    const rows = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?].?;
    const at = std.mem.indexOf(u8, rows.file.?.content, try std.fmt.bufPrint(&want, "{s}:3:", .{a})).?;
    const row = rows.file.?.content[at .. std.mem.indexOfScalarPos(u8, rows.file.?.content, at, '\n').?];
    try testing.expect(std.mem.endsWith(u8, row, " (closed)"));
    try testing.expectEqual(Status.ok, wr(p, Node.of(rows.serial, .look), try std.fmt.bufPrint(&line, "{s}\n", .{row[0 .. row.len - " (closed)".len]})).reply.status);
    p.sync();
    const back = p.panes[p.active].?;
    try testing.expectEqualStrings(a, back.file.?.path);
    try testing.expectEqual(@as(i32, 2), back.body.cur_row);
    // Closed again; the jumplist keeps its entry, closed, and a jump back
    // to it opens it again.
    _ = wr(p, Node.of(back.serial, .ctl), "Del\n");
    p.sync();
    var closed_entry = false;
    for (p.jumps[0..p.njumps]) |j| closed_entry = closed_entry or j.serial == 0;
    try testing.expect(closed_entry);
    var tries: usize = 0;
    while (tries < p.njumps) : (tries += 1) {
        p.jumpBy(-1);
        p.sync();
        if (p.panes[p.active].?.file) |f| if (std.mem.eql(u8, f.path, a)) break;
    }
    try testing.expectEqualStrings(a, p.panes[p.active].?.file.?.path);
}

test "Back and Forward over a closed file's entries: one reopen is that file's pane in every entry, so the next step moves" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    var long: [400]u8 = undefined;
    var n: usize = 0;
    for (0..100) |_| {
        @memcpy(long[n..][0..4], "row\n");
        n += 4;
    }
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "a.txt", .data = long[0..n] });
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "b.txt", .data = "bee\n" });
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "c.txt", .data = "sea\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/b.txt\n", .{dir}));
    p.sync();
    const b_serial = p.panes[p.active].?.serial;
    // Two entries for a.txt, far apart in it.
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt:1\n", .{dir}));
    p.sync();
    const a = p.active;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt:90\n", .{dir}));
    p.sync();
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/c.txt\n", .{dir}));
    p.sync();
    const c_serial = p.panes[p.active].?.serial;
    _ = wr(p, Node.of(p.panes[a].?.serial, .ctl), "Del\n");
    p.sync();
    var closed: usize = 0;
    for (p.jumps[0..p.njumps]) |j| closed += @intFromBool(j.serial == 0);
    try testing.expectEqual(@as(usize, 2), closed);
    // Back reopens it at line 90: both its entries are that pane now.
    p.jumpBy(-1);
    p.sync();
    const re = p.panes[p.active].?;
    try testing.expect(std.mem.endsWith(u8, re.file.?.path, "/a.txt"));
    try testing.expectEqual(@as(i32, 89), re.body.cur_row);
    for (p.jumps[0..p.njumps]) |j| try testing.expect(j.serial != 0);
    // Back again goes to its line 1, in the same pane, then to b.
    p.jumpBy(-1);
    p.sync();
    try testing.expectEqual(re.serial, p.panes[p.active].?.serial);
    try testing.expectEqual(@as(i32, 0), re.body.cur_row);
    p.jumpBy(-1);
    p.sync();
    try testing.expectEqual(b_serial, p.panes[p.active].?.serial);
    // And Forward walks it all again, to c.
    p.jumpBy(1);
    p.sync();
    p.jumpBy(1);
    p.sync();
    try testing.expectEqual(@as(i32, 89), re.body.cur_row);
    p.jumpBy(1);
    p.sync();
    try testing.expectEqual(c_serial, p.panes[p.active].?.serial);
}

test "Recent keeps only files on disk: not a name never saved, nor the served tree's" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "real.txt", .data = "real\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    const names = [_][]const u8{ try std.fmt.allocPrint(testing.allocator, "{s}/c", .{dir}), try testing.allocator.dupe(u8, "/virtual/zz"), try std.fmt.allocPrint(testing.allocator, "{s}/real.txt", .{dir}) };
    defer for (names) |n| testing.allocator.free(n);
    for (names) |name| {
        const made = try th.newPane(p);
        _ = wr(p, Node.of(made, .name), try std.fmt.bufPrint(&line, "{s}\n", .{name}));
        p.sync();
        _ = wr(p, Node.of(made, .ctl), "Del\n");
        _ = wr(p, Node.of(made, .ctl), "Del\n");
        p.sync();
    }
    try testing.expect(p.recent.get(names[0]) == null);
    try testing.expect(p.recent.get(names[1]) == null);
    try testing.expect(p.recent.get(names[2]) != null);
}

test "a new file saved shows in /recent, open, while it is" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    // A host that writes files, as the real ones do.
    const Writing = struct {
        fn write(_: ?*anyopaque, _: u8, path: []const u8, bytes: []const u8) void {
            std.Io.Dir.cwd().writeFile(testing.io, .{ .sub_path = path, .data = bytes }) catch {};
        }
    };
    p.host = .{ .vtable = &.{ .write_file = Writing.write } };
    defer p.host = .{};
    const made = try th.newPane(p);
    var line: [4200]u8 = undefined;
    const path = try std.fmt.bufPrint(&line, "{s}/new.txt", .{dir});
    var name: [4200]u8 = undefined;
    _ = wr(p, Node.of(made, .name), try std.fmt.bufPrint(&name, "{s}\n", .{path}));
    _ = wr(p, Node.of(made, .body), "fresh\n");
    try testing.expectEqual(Status.ok, wr(p, Node.of(made, .ctl), "Save\n").reply.status);
    p.perform(.{ .save_file = .{ .pane = @intCast(p.paneBySerial(made).?) } });
    var want: [4300]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, rd(p, @intFromEnum(tree.TopFile.recent), 0, 8192).bytes, try std.fmt.bufPrint(&want, "open {s}\n", .{path})) != null);
}

test "/recent shows a name as /index does, a newline in it escaped" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.recent.opened(p.recentGpa(), "/tmp/a\nb\\c");
    const text = rd(p, @intFromEnum(tree.TopFile.recent), 0, 8192).bytes;
    try testing.expect(std.mem.indexOf(u8, text, "closed /tmp/a\\nb\\\\c\n") != null);
}

test "Back over a closed file deleted since skips it, says so, and goes on to the place before" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    for ([_][]const u8{ "a.txt", "gone.txt", "c.txt" }) |name| try tmp.dir.writeFile(testing.io, .{ .sub_path = name, .data = "text\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/a.txt\n", .{dir}));
    p.sync();
    const a_serial = p.panes[p.active].?.serial;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/gone.txt\n", .{dir}));
    p.sync();
    const gone = p.active;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/c.txt\n", .{dir}));
    p.sync();
    const c_id = p.active;
    _ = wr(p, Node.of(p.panes[gone].?.serial, .ctl), "Del\n");
    p.sync();
    try tmp.dir.deleteFile(testing.io, "gone.txt");
    p.active = c_id;
    p.jumpBy(-1);
    p.sync();
    try testing.expectEqual(a_serial, p.panes[p.active].?.serial);
    try testing.expect(std.mem.indexOf(u8, p.panes[c_id].?.msg[0..p.panes[c_id].?.msg_len], "gone.txt: deleted, skipped") != null);
}

test "a remembered place is clamped to the file as it is now, its selection's two ends kept where they fit" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "c.txt", .data = "one\ntwo\nthree\nfour\nfive\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    _ = wr(p, root_look, try std.fmt.bufPrint(&line, "{s}/c.txt:2\n", .{dir}));
    p.sync();
    const c = p.panes[p.active].?;
    // A selection over lines 2 to 4, then closed.
    @import("pane.zig").setDot(c, .{ .q0 = 4, .q1 = 19 });
    try testing.expect(c.body.vsel.active);
    _ = wr(p, Node.of(c.serial, .ctl), "Del\n");
    p.sync();
    // The file shrinks to two lines while it is closed.
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "c.txt", .data = "one\ntwo\n" });
    _ = wr(p, root_exec, "Recent\n");
    const rows = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, std.mem.trimEnd(u8, rd(p, root_exec, 0, 64).bytes, "\n"), 10)).?].?;
    const at = std.mem.indexOf(u8, rows.file.?.content, "c.txt:").?;
    const row = rows.file.?.content[at .. std.mem.indexOfScalarPos(u8, rows.file.?.content, at, '\n').?];
    // Both ends are in the row, a range.
    try testing.expect(std.mem.indexOfScalar(u8, row, '-') != null);
    var full: [4400]u8 = undefined;
    const loc = try std.fmt.bufPrint(&full, "{s}/{s}\n", .{ dir, row[0 .. std.mem.indexOfScalar(u8, row, ' ').?] });
    // A look at it opens the file, never a miss, clamped to its last line.
    try testing.expectEqual(Status.ok, wr(p, Node.of(rows.serial, .look), loc).reply.status);
    p.sync();
    const back = p.panes[p.active].?;
    try testing.expect(std.mem.endsWith(u8, back.file.?.path, "/c.txt"));
    try testing.expect(back.body.cur_row <= 1);
    try testing.expect(back.body.vsel.active);
    // Its ends clamped to the last character, `two`'s `o`, not its newline.
    try testing.expect(back.body.cur_col <= 2 and back.body.vsel.col <= 2);
    try testing.expect(std.mem.indexOf(u8, back.msg[0..back.msg_len], "c.txt has 2 lines now: at its last") != null);
    // The same row with the file open: the same place, said the same way.
    _ = wr(p, Node.of(rows.serial, .look), loc);
    p.sync();
    try testing.expectEqual(back.serial, p.panes[p.active].?.serial);
    try testing.expect(back.body.cur_row <= 1);
    try testing.expect(std.mem.indexOf(u8, back.msg[0..back.msg_len], "at its last") != null);
}

test "size is monotonic: growing is never refused, and a size once taken is taken again" {
    const p = try Pardes.init(testing.allocator, .{ .tty_only = true, .cols = 160, .rows = 60 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    p.unattended = true;
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    const new = @intFromEnum(tree.TopFile.new);
    // The dogfood's repro: Newcol, three pane/new, a Tty, then pane/new
    // until a column has no room (ENOSPC).
    try testing.expectEqual(Status.ok, wr(p, root_ctl, "Newcol\n").reply.status);
    for (0..3) |_| try testing.expectEqual(Status.ok, call(p, .{ .tag = 1, .op = .open, .node = new }).reply.status);
    try testing.expectEqual(Status.ok, wr(p, Node.of(p.panes[p.active].?.serial, .ctl), "Tty\n").reply.status);
    p.sync();
    while (call(p, .{ .tag = 1, .op = .open, .node = new }).reply.status == .ok) p.sync();
    p.sync();
    var line: [32]u8 = undefined;
    // Down a row at a time (59, 58, 57, 56 and on) until one is refused:
    // once refused, every smaller one is too.
    var taken: [60]bool = @splat(false);
    var rows: u16 = 59;
    var refused = false;
    while (rows >= 20) : (rows -= 1) {
        taken[rows] = wr(p, root_ctl, try std.fmt.bufPrint(&line, "size 160 {d}\n", .{rows})).reply.status == .ok;
        if (refused) try testing.expect(!taken[rows]);
        if (!taken[rows]) refused = true;
    }
    try testing.expect(refused); // the columns are full: some size is too small
    // Back up: each size is taken again exactly when it was on the way down.
    rows = 20;
    while (rows <= 59) : (rows += 1) {
        const ok = wr(p, root_ctl, try std.fmt.bufPrint(&line, "size 160 {d}\n", .{rows})).reply.status == .ok;
        try testing.expectEqual(taken[rows], ok);
    }
    for ([_]u16{ 60, 61, 64, 70, 100 }) |grown| {
        try testing.expectEqual(Status.ok, wr(p, root_ctl, try std.fmt.bufPrint(&line, "size 160 {d}\n", .{grown})).reply.status);
        try testing.expectEqual(grown, p.screen_h);
    }
    // Out of range is EINVAL, in words 9ns reads as that.
    const bad = wr(p, root_ctl, "size 5 2\n");
    try testing.expectEqual(E.INVAL, bad.errno());
    try testing.expectStringStartsWith(bad.reply.ename, "invalid size");
}

test "Repl with no such language names a few whole, and where the rest are" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const refused = wr(p, Node.of(serialOf(p), .ctl), "Repl zzlang\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, "Repl: no language \"zzlang\"; - or one like zig ada bash c c_sharp clojure (") != null);
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, " more: docs/typ/reference.typ, REPLs)") != null);
}

test "a 10k-line Edit text block is taken in linear time and memory" {
    const gpa = testing.allocator;
    const p = try withFile(gpa, "x\n");
    defer p.deinit();
    var block: std.ArrayList(u8) = .empty;
    defer block.deinit(gpa);
    try block.appendSlice(gpa, "Edit $a\n");
    for (0..10_000) |i| try block.print(gpa, "line {d} of the block {{ with a brace }}\n", .{i});
    try block.appendSlice(gpa, ".\n");
    const started = std.Io.Clock.awake.now(std.testing.io);
    try testing.expectEqual(Status.ok, wr(p, Node.of(serialOf(p), .ctl), block.items).reply.status);
    const took = started.durationTo(std.Io.Clock.awake.now(std.testing.io)).toNanoseconds();
    try testing.expect(took < std.time.ns_per_s);
    try testing.expect(p.scratch.queryCapacity() < 50 * 1024 * 1024);
    try testing.expectEqual(@as(usize, 10_001), std.mem.count(u8, p.panes[0].?.file.?.content, "\n"));
}

test "a file changed on disk under unsaved edits is not reloaded: it says so, get asks, Save warns once" {
    const p = try withFile(testing.allocator, "one\n");
    defer p.deinit();
    const serial = serialOf(p);
    const f = &p.panes[0].?.file.?;
    // Clean, it takes the new text.
    pardes.panes.File.changed(p, 0, "two\n");
    try testing.expectEqualStrings("two\n", f.content);
    var reloaded: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&reloaded, "changed {d} reloaded\n", .{serial})));
    // Edited, it keeps its text and stays dirty.
    _ = wr(p, Node.of(serial, .body), "mine\n");
    pardes.panes.File.changed(p, 0, "three\n");
    try testing.expectEqualStrings("two\nmine\n", f.content);
    try testing.expect(f.revision != f.saved_revision);
    try testing.expect(th.logHas(p, "changed on disk (get reloads it, Save overwrites it)"));
    var want: [32]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "changed {d}\n", .{serial})));
    // Exit and get still ask about the edits.
    try testing.expectEqual(Status.err, wr(p, @intFromEnum(tree.TopFile.ctl), "Exit\n").reply.status);
    try testing.expect(std.mem.indexOf(u8, wr(p, Node.of(serial, .ctl), "get\n").reply.ename, "Modified") != null);
    // Save warns once before overwriting the newer file, then writes.
    const first = wr(p, Node.of(serial, .ctl), "Save\n");
    try testing.expectEqual(Status.err, first.reply.status);
    try testing.expect(std.mem.indexOf(u8, first.reply.ename, "modified on disk since read") != null);
    try testing.expect(wr(p, Node.of(serial, .ctl), "Save\n").saved);
}

test "a looked word is found in its own pane, next place after the dot, wrapping, and opens no pane" {
    const p = try withFile(testing.allocator, "foo x foo y\n");
    defer p.deinit();
    const serial = serialOf(p);
    const look_node = Node.of(serial, .look);
    const dot = Node.of(serial, .dot);
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    for ([_][]const u8{ "          0           3 ", "          6           9 ", "          0           3 " }) |want| {
        try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
        try testing.expectEqualStrings(want, rd(p, dot, 0, 64).bytes);
    }
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    // LookWord list: the +Search listing, as before.
    try testing.expect(p.executeBuiltinLine(0, "LookWord list"));
    try testing.expectEqual(Status.ok, wr(p, look_node, "foo\n").reply.status);
    after = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expect(after > count);
    // ...and look reads back that +Search pane, where the places are.
    var listed = false;
    var rows = std.mem.tokenizeScalar(u8, rd(p, look_node, 0, 256).bytes, '\n');
    while (rows.next()) |row| {
        const made = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, row, 10)).?].?;
        if (made.file) |f| if (f.output) |o| if (o.from == .search) {
            listed = true;
        };
    }
    try testing.expect(listed);
}

test "every word's /commands description is its own doc comment's first sentence, no citation" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const listed = rd(p, @intFromEnum(tree.TopFile.commands), 0, 1 << 16).bytes;
    for ([_][]const u8{
        "\nRepl arg pane -- Binds this terminal as a language's REPL, so an exec on that language's files is typed into it instead of run.\n",
        "\nJoincol root -- Fold the active pane's column into the one on its right, keeping its panes.\n",
        "\nExit root -- Quit the editor, refusing once while a pane holds unsaved text: an Exit with nothing edited since discards it.\n",
        "\nColors arg root on,off -- Syntax colours in text panes, on or off.\n",
        // the reference's examples, as they read.
        "\nNewcol root -- An empty column right of the keyboard's, its tag taking the keyboard.\n",
        "\nSave arg pane -- Write the pane's text to its file, or to the file its argument names.\n",
        "\nVerbose arg root on,off -- A builtin says its own name on the message row as it runs, on or off.\n",
        "\nPlacement arg root acme,pardes -- Where a new pane goes: acme, as makenewwindow does, or pardes, the older rules.\n",
        "\nKill arg root -- acme's Kill: stop the commands pardes started",
    }) |row| try testing.expect(std.mem.indexOf(u8, listed, row) != null);
    try testing.expect(std.mem.indexOf(u8, listed, ".c:") == null);
    // Every description is the first sentence of the doc comment just
    // above its word's declaration in builtins.zig.
    const source = @embedFile("../builtins.zig");
    var it = std.mem.tokenizeScalar(u8, listed, '\n');
    var undescribed: usize = 0;
    while (it.next()) |line| {
        // Every builtin has one: a word nobody can look up is no use.
        const dashes = std.mem.indexOf(u8, line, " -- ") orelse {
            std.debug.print("no doc comment: {s}\n", .{line});
            undescribed += 1;
            continue;
        };
        const word = line[0 .. std.mem.indexOfScalar(u8, line, ' ').?];
        if (config.Runtime.find(word)) |setting| {
            try testing.expect(std.mem.endsWith(u8, line, setting.doc));
            continue;
        }
        var needle: [64]u8 = undefined;
        const at = std.mem.indexOf(u8, source, try std.fmt.bufPrint(&needle, "\npub const {s} = struct", .{word})).?;
        const said = std.mem.trimEnd(u8, line[dashes + 4 ..], "…");
        // Its opening words are in the comment block right above.
        const head = said[0..@min(said.len, 10)];
        const block_start = std.mem.lastIndexOf(u8, source[0..at], "\n\n") orelse 0;
        try testing.expect(std.mem.indexOf(u8, source[block_start..at], head) != null);
    }
    try testing.expectEqual(0, undescribed);
}

test "Newcol at the column cap fails the write and says the cap" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.{ .resize = .{ .cols = 4000, .rows = 30 } });
    const root_ctl = @intFromEnum(tree.TopFile.ctl);
    while (p.ncol < pardes.MAX_COLS) {
        // From the widest column's tag, so no column gets too narrow first.
        p.sync();
        var widest: usize = 0;
        for (0..p.ncol) |c| if (p.col_w[c] > p.col_w[widest]) {
            widest = c;
        };
        pardes.tagline.enterHeader(p, widest);
        try testing.expectEqual(Status.ok, wr(p, root_ctl, "Newcol\n").reply.status);
    }
    const refused = wr(p, root_ctl, "Newcol\n");
    try testing.expectEqual(Status.err, refused.reply.status);
    var want: [64]u8 = undefined;
    try testing.expect(std.mem.indexOf(u8, refused.reply.ename, try std.fmt.bufPrint(&want, "no space for a column: {d} max", .{pardes.MAX_COLS})) != null);
    try testing.expect(th.logHas(p, "no space for a column"));
}

test "Save on a terminal asked over 9P is an ask in the log, answered with a path, and not asked twice" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const serial = serialOf(p);
    const id = p.paneBySerial(serial).?;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .tagexec), "Save\n").reply.status);
    var want: [48]u8 = undefined;
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "ask {d} save path\n", .{serial})));
    try testing.expect(p.panes[id].?.prompt == .save);
    // Again: the one open stands, one ask in the log.
    _ = wr(p, Node.of(serial, .tagexec), "Save\n");
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    try testing.expectEqual(@as(usize, 1), std.mem.count(u8, call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes, "save path\n"));
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
    // Answered: the path is written to, the prompt goes.
    const answered = wr(p, Node.of(serial, .ctl), "answer /tmp/pardes-ask-save.txt\n");
    try testing.expectEqual(Status.ok, answered.reply.status);
    try testing.expect(p.panes[id].?.prompt == .none);
    try testing.expect(th.logHas(p, try std.fmt.bufPrint(&want, "answer {d} /tmp/pardes-ask-save.txt\n", .{serial})));
}

test "get names the path it could not read, logs the edits it threw away, and a deleted file is said once" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const serial = serialOf(p);
    const f = &p.panes[0].?.file.?;
    const path = f.path;
    // Its file is not on disk: get names it.
    const missing = wr(p, Node.of(serial, .ctl), "get\n");
    try testing.expectEqual(E.NOENT, missing.errno());
    var want: [512]u8 = undefined;
    try testing.expectEqualStrings(try std.fmt.bufPrint(&want, "get: {s}: no such file", .{path}), missing.reply.ename);
    // Deleted on disk: said once.
    pardes.panes.File.deleted(p, 0);
    pardes.panes.File.deleted(p, 0);
    var rec: [32]u8 = undefined;
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    try testing.expectEqual(@as(usize, 1), std.mem.count(u8, call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes, try std.fmt.bufPrint(&rec, "changed {d} deleted\n", .{serial})));
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
}

test "a builtin that fails through exec, tagexec or a column's exec fails the write with one err and no msg" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.update(.tick); // the pane's `new` is logged first
    while (p.nextEffect()) |_| {}
    const serial = serialOf(p);
    for ([_]u64{ root_exec, Node.of(serial, .exec), @intFromEnum(tree.TopFile.tagexec), Node.ofCol(pardes.layout.columnSerial(p, 0), .exec) }) |node| {
        const failed = wr(p, node, "Unmount zzz\n");
        try testing.expectEqual(Status.err, failed.reply.status);
        try testing.expect(std.mem.indexOf(u8, failed.reply.ename, "Unmount: no such mount zzz") != null);
    }
    const log = @intFromEnum(tree.TopFile.log);
    const h = call(p, .{ .tag = 1, .op = .open, .node = log }).reply.handle;
    const text = call(p, .{ .tag = 2, .op = .read, .node = log, .handle = h, .size = 1 << 16 }).bytes;
    try testing.expect(std.mem.indexOf(u8, text, "msg ") == null);
    // The root's exec ran at the pane, so its err and the pane's exec's are
    // the same record, counted.
    try testing.expectEqual(@as(usize, 3), std.mem.count(u8, text, "Unmount: no such mount zzz"));
    try testing.expect(std.mem.indexOf(u8, text, "mount zzz (x2)") != null);
    _ = call(p, .{ .tag = 3, .op = .release, .node = log, .handle = h });
    // A control character is refused with its reason.
    try testing.expectEqualStrings(e_control, wr(p, root_exec, "Msg a\x01b\n").reply.ename);
    // A look miss: one err, no msg.
    _ = wr(p, @intFromEnum(tree.TopFile.look), "zzqqnotthere\n");
    try testing.expect(th.logHas(p, "look: no match for \"zzqqnotthere\""));
    try testing.expect(!th.logHas(p, "msg 1 Look: no match"));
    // The same miss again is that record counted, as any repeated err is.
    _ = wr(p, @intFromEnum(tree.TopFile.look), "zzqqnotthere\n");
    try testing.expect(th.logHas(p, "look: no match for \"zzqqnotthere\" (x2)\n"));
}

test "a word written to a raw terminal's look is listed as in normal mode" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const serial = serialOf(p);
    const id = p.paneBySerial(serial).?;
    p.update(.{ .output = .{ .pane = @intCast(id), .bytes = "one MARK two\r\n" } });
    p.panes[id].?.body.mode = .tty;
    try testing.expectEqual(Status.ok, wr(p, Node.of(serial, .look), "MARK\n").reply.status);
    const said = std.mem.trimEnd(u8, rd(p, Node.of(serial, .look), 0, 64).bytes, "\n");
    const made = p.panes[p.paneBySerial(try std.fmt.parseInt(u32, said, 10)).?].?;
    try testing.expect(made.file.?.output.?.from == .search);
}

test "@p<serial>:<address> takes any sam address; a miss and an unknown serial are errs" {
    const p = try withFile(testing.allocator, "foo x foo y\nbar\n");
    defer p.deinit();
    const serial = serialOf(p);
    const root = @intFromEnum(tree.TopFile.look);
    const dot = Node.of(serial, .dot);
    const Case = struct { addr: []const u8, want: []const u8 };
    for ([_]Case{
        .{ .addr = "0/foo/", .want = "          0           3 " },
        .{ .addr = "/foo/", .want = "          6           9 " },
        .{ .addr = "#12,#15", .want = "         12          15 " },
        .{ .addr = "$", .want = "         16          16 " },
        .{ .addr = "1,2", .want = "          0          16 " },
        // Backward, as in addr: from the dot's start, wrapping to the last.
        .{ .addr = "?foo?", .want = "          6           9 " },
        .{ .addr = "$-?y?", .want = "         10          11 " },
    }) |c| {
        var line: [64]u8 = undefined;
        try testing.expectEqual(Status.ok, wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:{s}\n", .{ serial, c.addr })).reply.status);
        try testing.expectEqualStrings(c.want, rd(p, dot, 0, 64).bytes);
    }
    var line: [64]u8 = undefined;
    _ = wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:/zzqq/\n", .{serial}));
    try testing.expect(th.logHas(p, ": no match for regexp"));
    try testing.expectEqualStrings("", rd(p, root, 0, 64).bytes);
    _ = wr(p, root, "@p999:/foo/\n");
    try testing.expect(th.logHas(p, "look: no pane @p999"));
    try testing.expectEqualStrings("", rd(p, root, 0, 64).bytes);
    // A line address to no pane is a miss too, not the active pane.
    _ = wr(p, root, "@p77:1\n");
    try testing.expect(th.logHas(p, "look: no pane @p77"));
    try testing.expectEqualStrings("", rd(p, root, 0, 64).bytes);
}

test "a look that goes to another pane leaves the looking pane's dot alone" {
    const p = try withFile(testing.allocator, "alpha bravo\ncharlie\n");
    defer p.deinit();
    const source = serialOf(p);
    const other = try th.newPane(p);
    _ = wr(p, Node.of(other, .body), "one\ntwo\nthree\n");
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "f.txt", .data = "f one\nf two\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var line: [4200]u8 = undefined;
    for ([_][]const u8{ "@p{d}:2", "@p{d}:/three/", "{s}/f.txt:2" }) |form| {
        @import("pane.zig").setDot(p.panes[p.paneBySerial(source).?].?, .{ .q0 = 6, .q1 = 11 });
        const text = if (form[0] == '@')
            (if (std.mem.eql(u8, form, "@p{d}:2")) try std.fmt.bufPrint(&line, "@p{d}:2\n", .{other}) else try std.fmt.bufPrint(&line, "@p{d}:/three/\n", .{other}))
        else
            try std.fmt.bufPrint(&line, "{s}/f.txt:2\n", .{dir});
        try testing.expectEqual(Status.ok, wr(p, Node.of(source, .look), text).reply.status);
        try testing.expect(p.active != p.paneBySerial(source).?);
        try testing.expectEqualStrings("          6          11 ", rd(p, Node.of(source, .dot), 0, 64).bytes);
    }
}

test "@p<terminal>:<address> takes any address over the terminal's lines, selecting the match" {
    const p = try th.withTerm(testing.allocator);
    defer p.deinit();
    const serial = serialOf(p);
    const id = p.paneBySerial(serial).?;
    p.update(.{ .output = .{ .pane = @intCast(id), .bytes = "one\r\ntwo MARK three\r\n" } });
    const pane = p.panes[id].?;
    const root = @intFromEnum(tree.TopFile.look);
    var line: [64]u8 = undefined;
    try testing.expectEqual(Status.ok, wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:0/MARK/\n", .{serial})).reply.status);
    try testing.expectEqual(@as(i32, 1), pane.body.cur_row);
    try testing.expect(pane.body.vsel.active);
    // #n lands on that byte: #5 is the `w` of `two`.
    try testing.expectEqual(Status.ok, wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:#5\n", .{serial})).reply.status);
    try testing.expectEqual(@as(i32, 1), pane.body.cur_row);
    try testing.expectEqual(@as(i32, 1), pane.body.cur_col);
    _ = wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:/zzqq/\n", .{serial}));
    try testing.expect(th.logHas(p, "look: no match for regexp"));
    // A line past its last is a miss, as in a file.
    const row_before = pane.body.cur_row;
    _ = wr(p, root, try std.fmt.bufPrint(&line, "@p{d}:999\n", .{serial}));
    try testing.expect(th.logHas(p, "has no line 999"));
    try testing.expectEqual(row_before, pane.body.cur_row);
    try testing.expectEqualStrings("", rd(p, root, 0, 64).bytes);
}

test "a bad command inside an Edit block written whole is named, not the } after it" {
    const p = try withFile(testing.allocator, "abc\n");
    defer p.deinit();
    const r = wr(p, Node.of(serialOf(p), .ctl), "Edit {\n,s/a/b/\nzq\n}\n");
    try testing.expectEqual(Status.err, r.reply.status);
    try testing.expect(std.mem.indexOf(u8, r.reply.ename, "\"}\"") == null);
    try testing.expect(std.mem.indexOf(u8, r.reply.ename, "z") != null);
    try testing.expectEqualStrings("abc\n", p.panes[0].?.file.?.content);
}

test "a refused Delcol changes nothing: no pane, no focus" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    _ = wr(p, @intFromEnum(tree.TopFile.ctl), "Newcol\n");
    const made = try th.newPane(p);
    _ = wr(p, Node.of(made, .name), "/tmp/pardes-delcol-refused.txt\n");
    _ = wr(p, Node.of(made, .body), "edit\n");
    p.sync();
    const col = layout.findPane(p, p.paneBySerial(made).?).?.col;
    const active = p.active;
    const active_column = p.active_column;
    var count: usize = 0;
    for (p.panes) |slot| count += @intFromBool(slot != null);
    try testing.expectEqual(Status.err, wr(p, Node.ofCol(layout.columnSerial(p, col), .ctl), "Delcol\n").reply.status);
    p.sync();
    var after: usize = 0;
    for (p.panes) |slot| after += @intFromBool(slot != null);
    try testing.expectEqual(count, after);
    try testing.expectEqual(active, p.active);
    try testing.expectEqual(active_column, p.active_column);
    try testing.expect(th.logHas(p, "unsaved "));
}

test "pager answers its +Pager on the open that asked, whatever another client exec'd meanwhile" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const pager = @intFromEnum(tree.TopFile.pager);
    const exec = @intFromEnum(tree.TopFile.exec);
    const asked = call(p, .{ .tag = 1, .op = .open, .node = pager, .omode = 2 }).reply.handle;
    try testing.expectEqual(Status.ok, call(p, .{ .tag = 2, .op = .write, .node = pager, .handle = asked, .data = "/tmp\n" }).reply.status);
    const paged = for (p.panes) |slot| {
        const pn = slot orelse continue;
        if (pn.file) |f| if (std.mem.eql(u8, f.path, "/tmp/+Pager")) break pn.serial;
    } else return error.NoPager;
    // Another client execs between the request and its read: a pane of its own.
    const racer = call(p, .{ .tag = 3, .op = .open, .node = exec, .omode = 2 }).reply.handle;
    try testing.expectEqual(Status.ok, call(p, .{ .tag = 4, .op = .write, .node = exec, .handle = racer, .data = "New\n" }).reply.status);
    var line: [16]u8 = undefined;
    const want = try std.fmt.bufPrint(&line, "{d}\n", .{paged});
    // A fresh open reads the session's last answer, the racer's pane: what
    // `pardes -` once read, and wrote its text into.
    try testing.expect(!std.mem.eql(u8, want, rd(p, exec, 0, 64).bytes));
    try testing.expectEqualStrings(want, call(p, .{ .tag = 5, .op = .read, .node = pager, .handle = asked, .size = 64 }).bytes);
    // Refused, the same open answers nothing, not its last answer.
    try testing.expectEqual(E.INVAL, call(p, .{ .tag = 6, .op = .write, .node = pager, .handle = asked, .data = "relative\n" }).errno());
    try testing.expectEqualStrings("", call(p, .{ .tag = 7, .op = .read, .node = pager, .handle = asked, .size = 64 }).bytes);
    // Resolved: `/tmp/../tmp/.` is /tmp's +Pager, the one made above.
    try testing.expectEqual(Status.ok, call(p, .{ .tag = 8, .op = .write, .node = pager, .handle = asked, .data = "/tmp/../tmp/.\n" }).reply.status);
    try testing.expectEqualStrings(want, call(p, .{ .tag = 9, .op = .read, .node = pager, .handle = asked, .size = 64 }).bytes);
    // One that may not be written is refused, permission denied.
    try testing.expectEqual(E.PERM, wr(p, pager, "/proc/1\n").errno());
    // One directory a write, absolute, and there.
    try testing.expectEqual(E.INVAL, wr(p, pager, "/a\n/b\n").errno());
    const relative = wr(p, pager, "relative\n");
    try testing.expectEqual(E.INVAL, relative.errno());
    try testing.expectEqualStrings("pager: invalid directory \"relative\": must be absolute", relative.reply.ename);
    try testing.expectEqual(E.NOENT, wr(p, pager, "/tmp/pardes-surely-missing-dir\n").errno());
}

test "a command pane an exec open was answered is leased to it while it stays open: another client's command gets a pane of its own" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const exec = Node.of(serialOf(p), .exec);
    const Client = struct {
        fn run(pp: *Pardes, node: u64, h: u32, line: []const u8) !usize {
            try testing.expectEqual(Status.ok, call(pp, .{ .tag = 2, .op = .write, .node = node, .handle = h, .data = line }).reply.status);
            const id = pp.paneBySerial(pp.fs.results[0]).?;
            // Its command finishes and its output ends.
            pp.panes[id].?.command_done = true;
            pp.panes[id].?.command_pty = false;
            return id;
        }
    };
    const a = call(p, .{ .tag = 1, .op = .open, .node = exec, .omode = 2 }).reply.handle;
    const b = call(p, .{ .tag = 1, .op = .open, .node = exec, .omode = 2 }).reply.handle;
    const a_pane = try Client.run(p, exec, a, "echo a\n");
    const b_pane = try Client.run(p, exec, b, "echo b\n");
    try testing.expect(a_pane != b_pane);
    // Each one's next command runs in its own pane again.
    try testing.expectEqual(a_pane, try Client.run(p, exec, a, "echo a2\n"));
    try testing.expectEqual(b_pane, try Client.run(p, exec, b, "echo b2\n"));
    // Closed, a lease ends: the directory's one command pane is reused.
    _ = call(p, .{ .tag = 3, .op = .release, .node = exec, .handle = a, .opened = true });
    try testing.expectEqual(Status.ok, wr(p, exec, "echo c\n").reply.status);
    try testing.expectEqual(a_pane, p.paneBySerial(p.fs.results[0]).?);
}

test "a Save whose directory is missing because one above refuses says permission denied, not no such directory" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    p.saveFailed(0, "/proc/1/root/x/f.txt", error.FileNotFound);
    try testing.expect(th.logHas(p, "Save /proc/1/root/x/f.txt: permission denied"));
    p.saveFailed(0, "/tmp/pardes-surely-missing-dir/f.txt", error.FileNotFound);
    try testing.expect(th.logHas(p, "no such directory"));
}

test "a body write to an image pane says its body takes none, not that terminals have no text" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const doc = try p.newDocPane(p.freeSlot().?);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    try testing.expectEqualStrings(pane_files.e_no_body, wr(p, Node.of(doc.serial, .body), "x").reply.ename);
}

test "Tty+bash on a pane ctl is Tty with its argument, as exec and the tag take it" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const r = call(p, .{ .tag = 1, .op = .write, .node = Node.of(serialOf(p), .ctl), .data = "Tty+sh\n" });
    try testing.expectEqual(Status.ok, r.reply.status);
    try testing.expect(r.spawned);
}

test "a Rename that reaches other files previews them, says so, and is the pane a waiting write answers" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const id = p.active;
    p.fs.lsp_result = null;
    p.lspRequest(id, .rename, "sum");
    p.lspResponse(p.lsp_wait.?.id, "lib.rs:2:8 sum\nmain.rs:4:13-15 sum\n");
    const preview = p.panes[p.panes[id].?.search_pane.?].?;
    try testing.expectEqual(preview.serial, p.fs.lsp_result.?);
    try testing.expect(th.logHas(p, "Rename: 2 edit(s) across files, previewed, not applied"));
}

test "Edit on an image pane is refused as a data write there is, EINVAL, before it runs" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const doc = try p.newDocPane(p.freeSlot().?);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    const edit = wr(p, Node.of(doc.serial, .ctl), "Edit ,d\n");
    const data = wr(p, Node.of(doc.serial, .data), "x");
    try testing.expectEqual(E.INVAL, edit.errno());
    try testing.expectEqualStrings(data.reply.ename, edit.reply.ename);
    try testing.expectEqual(E.INVAL, wr(p, Node.of(doc.serial, .name), "/tmp/other.ppm\n").errno());
}

test "`@pN:` looks at pane N as `a.txt:` looks at a.txt, and a line past the end is said one way, `:N` or `file:N`" {
    const p = try withFile(testing.allocator, "one\ntwo\n");
    defer p.deinit();
    const s = serialOf(p);
    var buf: [64]u8 = undefined;
    p.look_missed = false;
    pardes.look.lookAt(p, 0, try std.fmt.bufPrint(&buf, "@p{d}:", .{s}));
    try testing.expect(!p.look_missed);
    const f = pane_files.fileOf(p.panes[0].?).?;
    for ([_][]const u8{ ":99999", try std.fmt.bufPrint(&buf, "{s}:99999", .{f.path}) }) |looked| {
        pardes.look.lookAt(p, 0, looked);
        const said = p.panes[0].?.msg[0..p.panes[0].?.msg_len];
        try testing.expect(std.mem.endsWith(u8, said, "/test.txt:99999 has no line 99999"));
    }
}

test "a second LookWord list look in a directory refills its +Search rather than stacking another" {
    if (comptime !pardes.hosted) return;
    const gpa = testing.allocator;
    var tmp = testing.tmpDir(.{});
    defer tmp.cleanup();
    try tmp.dir.writeFile(testing.io, .{ .sub_path = "words.txt", .data = "alpha beta\nalpha beta\n" });
    var dir_buf: [4096]u8 = undefined;
    const dir = dir_buf[0..try tmp.dir.realPath(testing.io, &dir_buf)];
    var path_buf: [4200]u8 = undefined;
    const path = try std.fmt.bufPrint(&path_buf, "{s}/words.txt", .{dir});
    const p = try Pardes.init(gpa, .{ .file = path, .tty_only = true, .cols = 80, .rows = 30 });
    defer p.deinit();
    _ = wr(p, @intFromEnum(tree.TopFile.ctl), "LookWord list\n");
    pardes.look.lookAt(p, 0, "alpha");
    pardes.look.lookAt(p, 0, "beta");
    var searches: usize = 0;
    for (p.panes) |slot| if (slot) |pn| if (pn.file) |f| if (std.mem.endsWith(u8, f.path, "+Search")) {
        searches += 1;
        try testing.expectEqualStrings("beta", f.output.?.arg());
    };
    try testing.expectEqual(@as(usize, 1), searches);
}

test "Petscii, Palette and Ascii take the state their tag word names, set rather than flipped" {
    const p = try withFile(testing.allocator, "x\n");
    defer p.deinit();
    const doc = try p.newDocPane(p.freeSlot().?);
    doc.image = .{ .path = try p.gpa.dupe(u8, "/tmp/pardes-pic.ppm") };
    const ctl_node = Node.of(doc.serial, .ctl);
    for ([_][]const u8{ "Petscii on\n", "Petscii on\n" }) |line| {
        try testing.expectEqual(Status.ok, wr(p, ctl_node, line).reply.status);
        try testing.expect(doc.image.?.glyph_art);
    }
    _ = wr(p, ctl_node, "Petscii off\n");
    try testing.expect(!doc.image.?.glyph_art);
    _ = wr(p, ctl_node, "Palette terminal\n");
    _ = wr(p, ctl_node, "Palette terminal\n");
    try testing.expectEqual(pardes.panes.Image.PaletteMode.terminal, doc.image.?.pmode);
    _ = wr(p, ctl_node, "Ascii off\n");
    _ = wr(p, ctl_node, "Ascii off\n");
    try testing.expect(!doc.image.?.ascii);
    // Bare, each still flips.
    _ = wr(p, ctl_node, "Ascii\n");
    try testing.expect(doc.image.?.ascii);
    _ = wr(p, ctl_node, "Petscii maybe\n");
    try testing.expect(th.logHas(p, "Petscii takes on or off"));
}