Tty in a missing directory fails and makes no pane; a shell that never started answers runs

The host could not start the shell (its chdir failed), and the pane stayed
with no pty: a run written to it waited for a prompt for ever. Tty now
refuses a directory that is not there, `Tty: <dir>: no such directory`,
before making a pane; and a terminal whose shell the host could not start
(Pardes.shellFailed, from each host's spawn) answers any run with
`error shell gone`.

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

2 files changed, 35 insertions, 1 deletions

diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index 6a8a37be..9bb9c044 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -1746,6 +1746,37 @@ test "a root exec that fails logs its err against the pane it ran at" {
     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.IO, 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 "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();
diff --git a/src/ninep/pty.zig b/src/ninep/pty.zig
index 4009af49..68f98554 100644
--- a/src/ninep/pty.zig
+++ b/src/ninep/pty.zig
@@ -196,7 +196,10 @@ pub fn writeRun(p: *Pardes, req: Req, id: usize, pane: *Pane) Reply {
     const pf = &pane.fs;
     const state = pane.terminal orelse return tree.failText(req.tag, E.INVAL, e_bad_line);
     const marks = &state.stream.handler;
-    if (pane.command != null) {
+    if (pane.shell_failed) {
+        // Its shell never started: no prompt is coming to wait for.
+        answer(p, slot, "error shell gone", .{});
+    } else if (pane.command != null) {
         // Its child is the command, and no shell is there to take a line.
         answer(p, slot, "error {s}", .{if (pane.command_done) "command done; not a shell" else "a command runs here, not a shell"});
     } else if (pf.unmarked) {