A REPL takes text only while its program has the terminal

A binding outlived its program: a command pane reused kept the REPL of the
command before, a done command pane could be bound, a document pane (a
terminal with no emulator) was accepted, and after Ctrl-D in python3 the text
went to the shell, which ran import os as ImageMagick's. A command pane's
binding now ends with its command and a done one is refused, a pane with no
emulator is refused, and an interactive terminal's REPL is live only while a
program other than its shell holds the tty (the host's tty_taken); when none
of the language's REPLs is, nothing is sent or run and the pane says so.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 29 insertions, 7 deletions

diff --git a/src/exec.zig b/src/exec.zig
index dbda7217..57eaad8f 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -394,10 +394,15 @@ pub fn langOf(pane: *const Pane) ?u8 {
     return null;
 }
 
-/// A bound REPL whose program can still take input: a command pane's is
-/// gone once its command is done.
-pub fn replLive(pane: *const Pane) bool {
-    return pane.repl != null and pane.isTerminal() and !(pane.command != null and pane.command_done);
+/// A bound REPL whose program is there to take input: a command pane's
+/// while its command runs; an interactive terminal's while a program, not
+/// the shell, has its tty (the host's `tty_taken`) -- a python3 left with
+/// Ctrl-D leaves the shell, which would run `import os` as ImageMagick's.
+pub fn replLive(p: *const Pardes, id: usize) bool {
+    const pane = p.panes[id] orelse return false;
+    if (pane.repl == null) return false;
+    if (pane.command != null) return !pane.command_done;
+    return p.hostTtyTaken(id);
 }
 
 /// `python-a`.
@@ -408,22 +413,37 @@ pub fn replId(buf: []u8, pane: *const Pane) []const u8 {
 
 const Routed = union(enum) { none, sent: usize, asked };
 
+/// The REPL bound here has no program running to take the text: said,
+/// and nothing sent or run.
+fn replGone(p: *Pardes, from: usize, repl: *const Pane) Routed {
+    var idbuf: [48]u8 = undefined;
+    var said: [128]u8 = undefined;
+    p.setMessage(from, std.fmt.bufPrint(&said, "Repl: {s} has no program running; nothing sent", .{replId(&idbuf, repl)}) catch "Repl: no program running");
+    return .asked;
+}
+
 /// Where an exec from `from`'s body goes when a REPL is bound for it: the
 /// one there is, or a question when there are several.
 fn routeToRepl(p: *Pardes, from: usize, text: []const u8) Routed {
     const src = p.panes[from] orelse return .none;
-    if (src.repl != null and replLive(src)) {
+    if (src.repl != null) {
+        if (!replLive(p, from)) return replGone(p, from, src);
         sendToRepl(p, from, from, text);
         return .{ .sent = from };
     }
     const lang = langOf(src) orelse return .none;
     var bound: [26]usize = undefined;
     var n: usize = 0;
-    for (p.panes, 0..) |slot, i| if (slot) |pane| if (pane.repl) |r| if (r.lang == lang and replLive(pane) and n < bound.len) {
+    var gone: ?usize = null;
+    for (p.panes, 0..) |slot, i| if (slot) |pane| if (pane.repl) |r| if (r.lang == lang and n < bound.len) {
+        if (!replLive(p, i)) {
+            gone = i;
+            continue;
+        }
         bound[n] = i;
         n += 1;
     };
-    if (n == 0) return .none;
+    if (n == 0) return if (gone) |i| replGone(p, from, p.panes[i].?) else .none;
     if (n == 1) {
         sendToRepl(p, from, bound[0], text);
         return .{ .sent = bound[0] };
@@ -593,6 +613,8 @@ fn noteRun(p: *Pardes, pane: *Pane, what: []const u8, said: []const u8) void {
 pub fn commandDone(p: *Pardes, id: usize, status: ?u8) void {
     const pane = p.panes[id] orelse return;
     pane.command_done = true;
+    // A REPL it was is gone with its command; the pane's next is not one.
+    pane.repl = null;
     pane.command_status = status;
     pane.body.mode = .normal;
     var buf: [16]u8 = undefined;