fix(fuse): run a burst's named folders first and retry failed watches

A poll in the same burst as a new folder's Reconcile(id) took its place,
so the new folder waited behind a pass over every other one (B260).

A recursive watch that failed partway left its watches registered, was
never retried, and its events ran passes over every folder (B262). It
is now unwatched and retried every 10 minutes, symlinks are not followed,
and watcher errors are logged. A folder removed and added again in one
burst keeps its watch under the new id (B272).

crates/pdfs-fuse/src/sync.rs

@@ -48,11 +48,11 @@ mod engine;
 mod local_scan;
 mod model;
 mod planner;
-#[cfg(test)]
-use engine::Running;
 pub(crate) use engine::SYNC_CONCURRENCY;
 pub(crate) use engine::{EngineHealth, SyncMsg, spawn};
 #[cfg(test)]
+use engine::{Running, burst_order, keep_wanted};
+#[cfg(test)]
 use engine::{classify, event_target, settle_with};
 #[cfg(test)]
 use local_scan::is_write_mode;
@@ -2478,6 +2478,28 @@ mod tests {
         assert_eq!(health.report().panics, 1);
     }
 
+    /// Folders named by id run before the rest of a `ReconcileAll` in the
+    /// same burst, so a folder just added does not wait behind a pass over
+    /// every other folder (`docs/BUGS.md` B260).
+    #[test]
+    fn named_folders_run_before_the_rest_of_a_burst() {
+        let ids: HashSet<i64> = [9, 4].into();
+        assert_eq!(burst_order(&ids, &[1, 4, 6, 9]), [4, 9, 1, 6]);
+        assert_eq!(burst_order(&HashSet::new(), &[1, 4]), [1, 4]);
+        // A folder the list no longer has still gets the pass it asked for.
+        assert_eq!(burst_order(&[12].into(), &[1]), [12, 1]);
+    }
+
+    /// A folder removed and added again keeps its watch under the new id;
+    /// a folder that is gone loses its watch (`docs/BUGS.md` B272).
+    #[test]
+    fn a_re_added_folder_keeps_its_watch_under_the_new_id() {
+        let mut have = vec![(PathBuf::from("/a"), 1), (PathBuf::from("/b"), 2)];
+        let dropped = keep_wanted(&mut have, &[(PathBuf::from("/a"), 7)]);
+        assert_eq!(have, [(PathBuf::from("/a"), 7)]);
+        assert_eq!(dropped, [PathBuf::from("/b")]);
+    }
+
     /// While a pass runs, the report names its folder, which is what tells a
     /// long pass apart from an idle engine.
     #[test]