`> exec` through a mount no longer hangs the editor, and a close holding a last line is answered at once: the line runs at the editor's next step

A shell's truncating open of exec (or look, ctl, log, pager) sends a
setattr that changes nothing; it waited for the editor to be quiet, and
through a 9ns mount that quiet could never come: 9ns answers nothing else
on the mount while the setattr is out, and the editor's step may be out
reading a pane's file through it. This was the "truncating open of exec
hangs, only in selfmount" mystery. Only a truncate of a pane's file or a
tag waits now.

A close holding a last line with no newline hands it to the editor's step
(tree.runClosedLines, beside fillClosedPagers), as a /pager close does, and
is answered at once; a refusal is the log's err.

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

1 files changed, 1 insertions, 0 deletions

diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index e2ec31d1..c496571f 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -1571,6 +1571,7 @@ test "a name cut across writes is one name, applied once at its newline or its c
     _ = call(p, .{ .tag = 2, .op = .write, .node = node, .handle = h3, .data = "/tmp/pardes-closed.txt" });
     try testing.expectEqualStrings("/tmp/pardes-name.txt", nameOf(p, p.panes[p.paneBySerial(serial).?].?));
     _ = call(p, .{ .tag = 3, .op = .release, .node = node, .handle = h3, .opened = true });
+    tree.runClosedLines(p);
     try testing.expectEqualStrings("/tmp/pardes-closed.txt", nameOf(p, p.panes[p.paneBySerial(serial).?].?));
 }