pty/ctl exec fails the write when the shell cannot start; a directory removed under a shell leaves its name

`exec` on pty/ctl restarted a shell in a directory that was gone, the
write succeeding and the pane dead; and the pane was then renamed
`<dir> (deleted)` from /proc, so a restart failed even once the directory
was back. `exec` is now refused up front, ENOENT, where the directory is
gone; a shell the host cannot start fails the waiting write (late
failure, as a Save's); and a `(deleted)` cwd is no name to take.

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

1 files changed, 19 insertions, 0 deletions

diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index eea033ed..2f94dd3c 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -1949,6 +1949,25 @@ test "a command line from a missing directory fails ENOENT and makes no pane; a
     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 "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();