From f46e321ab4aabd7e643be0ee7c294c953bc470fa Mon Sep 17 00:00:00 2001
From: Garry Tan <garrytan@gmail.com>
Date: Tue, 18 Aug 2026 16:46:15 -0700
Subject: [PATCH] =?UTF-8?q?fix(settings-hook):=20GNU-first=20stat=20in=20t?=
 =?UTF-8?q?he=20lock=20stale=20check=20=E2=80=94=20Linux=20abort=20on=20he?=
 =?UTF-8?q?ld=20locks?=
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On Linux, BSD-style `stat -f %m` prints a multi-line FILESYSTEM block to
stdout before exiting 1, so the BSD-first || chain captured that garbage
concatenated with the real `stat -c %Y` epoch. The non-numeric mtime made
`$(( now - mtime ))` a syntax error and set -e killed the binary with
exit 1 whenever a lock dir already existed — every contention path (stale
takeover, give-up, concurrent writers) broke on CI while staying green on
macOS, where BSD stat -f succeeds cleanly.

GNU `stat -c %Y` now goes first (BSD stat rejects -c with no stdout, so
macOS falls through cleanly), and a numeric guard blanks any residual
garbage so a future platform quirk degrades to the normal give-up path
instead of an arithmetic abort. Same defect class as gstack-repo-mode's
GNU-first ordering (#2195). Verified in an oven/bun Linux container:
the four CI-failing lock tests now pass (62/62 across both files).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 bin/gstack-settings-hook | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/bin/gstack-settings-hook b/bin/gstack-settings-hook
index 56dd28828..6fd8b121a 100755
--- a/bin/gstack-settings-hook
+++ b/bin/gstack-settings-hook
@@ -265,7 +265,14 @@ _acquire_lock() {
     fi
     # Stale takeover: atomic rename means exactly one contender wins; the
     # loser loops and re-contends against the winner's fresh mkdir.
-    mtime=$(stat -f %m "$_LOCK_DIR" 2>/dev/null || stat -c %Y "$_LOCK_DIR" 2>/dev/null || echo "")
+    # GNU stat (-c %Y) first: on Linux, BSD-style `stat -f %m` prints a
+    # multi-line FILESYSTEM block to stdout before failing, and the || chain
+    # would capture that garbage alongside the real epoch. BSD stat rejects
+    # -c with no stdout, so macOS falls through cleanly. The numeric guard
+    # below makes any residual garbage inert (no takeover, normal give-up)
+    # instead of an arithmetic abort under set -e.
+    mtime=$(stat -c %Y "$_LOCK_DIR" 2>/dev/null || stat -f %m "$_LOCK_DIR" 2>/dev/null || echo "")
+    case "$mtime" in *[!0-9]*) mtime="" ;; esac
     now=$(date +%s)
     if [ -n "$mtime" ] && [ $(( now - mtime )) -gt "$stale_after_s" ]; then
       stale="$_LOCK_DIR.stale.$$-$RANDOM"