fix(fuse): end a mirror pass at the stop (B169)

A stop that came while a mirror pass was uploading let the pass go on to
the next level of folders until the stop gave up on it and the runtime's
end cancelled the uploads under it. Once the daemon is stopping, a batch
starts none of its waiting ops, lets the ones sending finish, and ends
the pass; the remote walk and a new pass stop too.

docs/BUGS.md

@@ -12,6 +12,32 @@ Conventions:
 
 ---
 
+## B169 — A stop lets a mirror pass go on until the runtime ends under it
+
+**Status:** Fixed.
+**Found:** 2026-10-04, in the journal of the account run on the working tree after B165. A
+stop that came while a mirror pass was uploading logged "background workers did not finish in
+time" for `pdfs-sync`, then "sync: task panicked … was cancelled" and a run of "no remote
+parent" warnings: the pass had gone on to deeper folders while the stop waited for it, and the
+runtime's end cancelled the uploads under it.
+
+**Where:** `flush_batch`, `walk_remote` and `reconcile_pass` in `crates/pdfs-fuse/src/sync.rs`.
+
+**Cause.** The mirror pass never asked whether the daemon was stopping. It sends its work a
+level of folders at a time and went on to the next level after the stop, until the stop gave up
+on it at its 10 s limit (B165).
+
+**Fix.** Once the daemon is stopping, a batch starts none of its ops still waiting for their
+turn, lets the ones already sending finish, and ends the pass. So do the remote walk and the
+start of a pass. The folder keeps the state it had before the pass; the next start's pass picks
+up from the baseline.
+
+**Test:** `a_stop_ends_a_mirror_pass_after_the_uploads_it_is_sending` in `sim/daemon.rs` holds a
+mirror upload, stops the daemon, then lets the upload through, and checks that the file in the
+deeper folder was not sent and the stop did not run into its limit.
+
+---
+
 ## B168 — A file removed with its folder while uploading is sent again, to the root
 
 **Status:** Fixed.