A shell that exits under a run answers exit N, and the log says exit before del

A dogfood agent ran `exit 3` through pty/run: the reader got ENOENT, and
the log went straight to del. The hosts now read a shell's exit status at
its pty's end as they do a command's; a run waiting on the line answers
`exit 3` with what it printed, the log says `exit <serial> 3` before
the pane's `del`, and an open run still stats after its pane is gone
(cat fstats its input). Pins cloud9 f35b7ed, whose stat of an open fid names
its open. Writes to a gone pane's pty/data, held open or not, fail ENOENT.

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

1 files changed, 19 insertions, 1 deletions

diff --git a/src/ninep/tree.zig b/src/ninep/tree.zig
index b3f3dde6..779ecff3 100644
--- a/src/ninep/tree.zig
+++ b/src/ninep/tree.zig
@@ -385,7 +385,7 @@ pub fn handle(p: *Pardes, req: Req) Reply {
     };
     return switch (req.op) {
         .lookup => lookup(p, req, target),
-        .getattr => .{ .tag = req.tag, .attr = attrOf(p, target) orelse return Reply.fail(req.tag, E.NOENT) },
+        .getattr => .{ .tag = req.tag, .attr = attrOf(p, target) orelse runAttr(p, req, target) orelse return Reply.fail(req.tag, E.NOENT) },
         .setattr => setattr(p, req, target),
         .open => open(p, req, target),
         .release => release(p, req),
@@ -395,6 +395,24 @@ pub fn handle(p: *Pardes, req: Req) Reply {
     };
 }
 
+/// A run's answer outlives its pane, so its file still stats while a run
+/// is open on it (a reader's fstat, cat's), as acme's fid keeps its window.
+/// The stat names the open when it came on one; a mount's comes on the
+/// file's walked name, and serials are never reused, so any run open on
+/// this node is the reader's.
+fn runAttr(p: *Pardes, req: Req, target: Target) ?Reply.Attr {
+    const t = switch (target) {
+        .pane => |t| t,
+        .top => return null,
+    };
+    if (t.file != .pty_run) return null;
+    const run = if (req.handle != 0) openOf(p, req) else for (&p.fs.opens) |*o| {
+        if (o.node == req.node and o.what == .run) break o;
+    } else null;
+    if ((run orelse return null).what != .run) return null;
+    return .{ .name = t.file.fileName(), .node = Node.of(t.serial, t.file), .mode = t.file.mode(), .mtime = p.fs.started };
+}
+
 fn attrOf(p: *Pardes, target: Target) ?Reply.Attr {
     switch (target) {
         .top => |f| return .{