On quit the lite controller's destructor never runs, because main()
ends the process with _Exit(). Any state the background refresh had
scanned since the last save was lost: the destructor is where that
final save would normally happen, and it was being skipped on the
one path that always runs.
- shutdown() now calls a new flushOnExit() that persists once on the
way out, bounded to 4 s so the existing 15 s shutdown watchdog
budget still holds. On timeout it abandons the save thread and lets
_Exit follow.
- It is a plain save through the same backend path, which writes a
temp file and renames it into place. That cannot corrupt the wallet
if it is cut off or abandoned, and it does not change the wallet
file format - it only persists sooner on the quit path.
- It reuses the destructor's guards and also skips when a wallet op
is already in progress: shutdown() has already waited for ops to go
idle, and a still-pending op holds the sync lock and issues its own
save, so flushOnExit would only block the budget on a save that
cannot take the lock.
Tests cover a save on the open, synced, idle path (exactly once), a
blocked save returning within the budget, and the retired and
never-opened guards skipping the save.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>