An event reader whose pane closes reads EOF, not ENOENT

A script following a pane's event in a loop ended in an error when the
pane went, though nothing had gone wrong: the pane was simply done. A
read on an event open whose pane has closed now answers no bytes, the
end a pipe's reader sees when its writer goes, so cat and while-read
end cleanly. pty/data keeps acme's answer.

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

2 files changed, 11 insertions, 7 deletions

diff --git a/src/ninep/events.zig b/src/ninep/events.zig
index 9d59e6cc..f5631adf 100644
--- a/src/ninep/events.zig
+++ b/src/ninep/events.zig
@@ -1010,10 +1010,10 @@ test "a pane deleted while its event file is open leaves no suppression behind"
     _ = wr(p, Node.of(serial, .ctl), "Del\n");
     try testing.expect(p.paneBySerial(serial) == null);
     try testing.expectEqual(@as(u16, 0), p.fs.listeners);
-    // The reader's next read hears what acme says of a window gone under it.
+    // The reader's next read is its end: no more records, no error.
     const shut = call(p, .{ .tag = 19, .op = .read, .node = event, .handle = a.reply.handle, .size = 64 });
-    try testing.expectEqual(E.NOENT, shut.errno());
-    try testing.expectEqualStrings(tree.e_shut_down, shut.reply.ename);
+    try testing.expectEqual(tree.Status.ok, shut.reply.status);
+    try testing.expectEqualStrings("", shut.bytes);
 
     _ = call(p, .{ .tag = 20, .op = .release, .node = event, .handle = a.reply.handle });
     _ = call(p, .{ .tag = 21, .op = .release, .node = event, .handle = b.reply.handle });
diff --git a/src/ninep/tree.zig b/src/ninep/tree.zig
index 8c536c51..c71a706f 100644
--- a/src/ninep/tree.zig
+++ b/src/ninep/tree.zig
@@ -1094,10 +1094,14 @@ fn readFile(p: *Pardes, req: Req, target: Target) Reply {
             // A run's answer outlives the pane it ran in.
             if (t.file == .pty_run and req.handle != 0) return pty.readRun(p, req);
             const id = p.paneBySerial(t.serial) orelse {
-                // An event or pty/data read the pane closed under: acme's
-                // answer to the same (editors/acme/xfid.c:1005).
-                if (openOf(p, req)) |o| if (o.what == .event or o.what == .pty_data)
-                    return failText(req.tag, E.NOENT, e_shut_down);
+                // An event reader whose pane closed reads its end: there
+                // are no more records, as a pipe's writer gone is EOF, so
+                // `while read` and `cat` end cleanly. A pty/data read the
+                // pane closed under keeps acme's answer (xfid.c:1005).
+                if (openOf(p, req)) |o| {
+                    if (o.what == .event) return .{ .tag = req.tag };
+                    if (o.what == .pty_data) return failText(req.tag, E.NOENT, e_shut_down);
+                }
                 return Reply.fail(req.tag, E.NOENT);
             };
             const pn = p.panes[id].?;