Fix post-merge audit findings; unify staging teardown

Audit
-----
- create_task.py verify failed on a DEFAULT install. hook_status.json emitted a
  per-file entry for the nested module with ok:false whenever the feature was
  switched off -- the default -- so verify printed [FAIL] and exited 1, right
  after the README tells users to run it. Status is now per MODULE with an
  `active` flag, and verify renders an inactive module as [SKIP].

- A partial apply suppressed the middlewared restart. The exit code conflated
  "nothing applied" with "one module applied, one failed", so a failing providers
  patch would prevent the restart that a freshly-applied nested patch needs,
  leaving it on disk and never loaded. Exit 2 now means partial and the restart
  still fires.

- The native-nested probe could never fire. It scanned crud.py for the guard
  message, but our own injected block quotes that message, so once applied the
  probe would always conclude the guard was still present. It now reads only the
  stock portion of the file.

- recover.sh did not unmount staging trees, so an emergency recovery left bind
  mounts pinning ZFS snapshots that could then never be destroyed.

- uninstall.sh deleted sidecar files without reading them. A sidecar is the only
  record that an interrupted run's snapshot tree is still on disk; both scripts
  now name the snapshot before clearing it.

- Removed a dead branch in the restart gate (unreachable: the kill switch exits).

Refactor
--------
- Staging teardown had been copy-pasted into uninstall.sh and recover.sh -- two
  untested shell copies of the fiddly depth-ordering and lazy-umount logic. Both
  now call `python3 patch/truecloud_nested.py cleanup`, so there is exactly one
  implementation and it is the one under test.

- Dropped the in-memory ACTIVE dict. The sidecar file was already the source of
  truth; a second in-process record could only desync -- and it is precisely the
  middlewared-restart case (which empties it) that must not orphan a snapshot
  tree. One record, on disk, or none.

Not done: the overlay-unmount loop is duplicated across apply.sh/uninstall.sh/
recover.sh. It is pre-existing, and apply.sh runs at PREINIT under a tight
timeout -- giving it a source dependency would trade 10 lines of duplication for
a boot-time failure mode.

74 tests, ruff and shellcheck clean.

CHANGELOG.md

@@ -123,6 +123,40 @@
 - `patch/__pycache__/create_task.cpython-314.pyc` was committed to the
   repository; it is now untracked and `__pycache__/` is gitignored.
 
+### Fixed (post-merge audit)
+
+- **`create_task.py verify` failed on a default install.** `hook_status.json`
+  emitted a per-file entry for the nested module with `ok: false` whenever the
+  feature was switched off — which is the default — so `verify` printed `[FAIL]`
+  and exited 1 right after the README told users to run it. Status is now
+  reported per *module* with an `active` flag, and `verify` renders an inactive
+  module as `[SKIP]` rather than a failure.
+- **A partial apply suppressed the middlewared restart.** The exit code
+  conflated "nothing applied" with "one module applied, one failed", so a failing
+  providers patch would prevent the restart that a freshly-applied nested patch
+  needs — leaving it on disk and never loaded. Exit 2 now means partial, and the
+  restart still fires.
+- **The native-nested probe could never fire.** It scanned `crud.py` for the
+  guard message, but our own injected block *quotes* that message, so once
+  applied the probe would always conclude the guard was still present. It now
+  reads only the stock portion of the file.
+- `recover.sh` did not unmount staging trees, so an emergency recovery left bind
+  mounts pinning ZFS snapshots that could then never be destroyed.
+- `uninstall.sh` deleted sidecar files without reading them. A sidecar is the
+  only record that an interrupted run's snapshot tree is still on disk; both
+  scripts now name the snapshot (`zfs destroy -r ...`) before clearing it.
+
+### Refactored
+
+- Staging teardown had been copy-pasted into `uninstall.sh` and `recover.sh` —
+  two untested shell copies of the fiddly depth-ordering and lazy-umount logic.
+  Both now call `python3 patch/truecloud_nested.py cleanup`, so there is one
+  implementation and it is the one under test.
+- Dropped the in-memory `ACTIVE` dict. The sidecar file was already the source of
+  truth; a second in-process record could only desync — and it is the
+  middlewared-restart case (which empties it) that must not orphan a snapshot
+  tree. One record, on disk, or none.
+
 ### Known issues
 
 - Stock `restic_backup()` deletes the ZFS snapshot in its own `finally`, which