A command from a missing directory fails ENOENT with no pane; one whose shell never started ends exit 127

Exec made a command pane in a directory that was not there, whose shell
never started: it said running for ever, a follower waited for an exit
that never came, and Kill found it. The line now fails up front, as Tty
does, `exec: <dir>: no such directory`; and a command pane whose shell
the host could not start ends `exit 127` at once. A shell that could not
start in its directory says `directory missing`, not `file not found`.

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

1 files changed, 18 insertions, 2 deletions

diff --git a/src/exec.zig b/src/exec.zig
index ebe90b98..79717963 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -351,11 +351,11 @@ fn spawnTtyWithMount(p: *Pardes, from: usize, v9fs: bool) ?*Pane {
     // start in it, and a dead pane would answer no run. Asked only of a host
     // that starts shells (none, as in the core's tests, starts none).
     const dir = p.execDir(from);
-    if (comptime hosted) if (p.host.vtable.spawn != null) if (@import("fs.zig").localPath(dir)) |local| if (!isDirectory(local)) {
+    if (missingDir(p, dir)) {
         var said: [pardes.memory.limits.host_path_cap + 48]u8 = undefined;
         p.reportFailure(from, std.fmt.bufPrint(&said, "Tty: {s}: no such directory", .{dir}) catch "Tty: no such directory");
         return null;
-    };
+    }
     const free = p.freeSlot() orelse {
         p.reportError(from, "Tty", error.NoPaneSlots);
         return null;
@@ -375,6 +375,15 @@ fn spawnTtyWithMount(p: *Pardes, from: usize, v9fs: bool) ?*Pane {
     return nt;
 }
 
+/// Whether a shell would be started in `dir` and `dir` is not there: asked
+/// only of a host that starts shells, and only of a local path.
+pub fn missingDir(p: *Pardes, dir: []const u8) bool {
+    if (comptime !hosted) return false;
+    if (p.host.vtable.spawn == null) return false;
+    const local = @import("fs.zig").localPath(dir) orelse return false;
+    return !isDirectory(local);
+}
+
 /// Whether `path` is a directory on this host, the turn out while it asks
 /// (it may be inside a mount this editor serves).
 pub fn isDirectory(path: []const u8) bool {
@@ -662,6 +671,13 @@ fn runCommand(p: *Pardes, from: usize, line: []const u8) ?usize {
     }
     const src = p.panes[from] orelse return null;
     const dir = p.execDir(from);
+    // A directory that is not there runs nothing, as Tty makes nothing
+    // there: no pane, and the write fails ENOENT.
+    if (missingDir(p, dir)) {
+        var said: [pardes.memory.limits.host_path_cap + 48]u8 = undefined;
+        p.reportFailure(from, std.fmt.bufPrint(&said, "exec: {s}: no such directory", .{dir}) catch "exec: no such directory");
+        return null;
+    }
     // Not one whose pty a job it left behind still prints to: reusing it
     // would hang that job up.
     // From a column's tag, only a finished pane in that column is reused,