v0.263.0: a failed update puts the app back by itself (09 decision 15, R-637)

The guarded update gains a folder copy of the app's named volumes, taken
after the pull where the app stops anyway (decision 19, chosen by the
2026-09-23 bake-off). On a failed health check the box undoes: every copy
validated by its finished-marker first, volumes refilled, definition and pin
from the job's own pre-update copies, the old version checked with the OLD
.felhom.yml probe. It holds only if the undo fails, and the hold sentence
says so and what state the data is in. Bind-mounted folders are never
touched.

- R-637 built; R-638/R-640/R-641 do not arise with a folder copy; R-639
  (pre-update copies incl. .felhom.yml kept until the undo is over).
- journal phases copying/undoing with power-cut recovery.
- app.yaml last_update_undone + one line on the app page (hu/en).
- R-642: start/restart never answer "completed".
- Removal deletes kept undo copies.

MinAgent unchanged (0.131.0). Nine red-proofs in REPORT.md.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/scripts/docker_run_volume_path_gate.py

@@ -35,6 +35,16 @@ ALLOWLIST = [
     ("internal/backup/restore.go", '"-v", dumpDir+":/in:ro"',
      "Tier-1 volume restore source: same registered-drive namespace argument as the dump "
      "target above — host-visible by the identical binds"),
+    ("internal/stacks/undo.go", '"-v", vol+":/v:ro"',
+     "the undo's size check (v0.263.0): `du` on a NAMED volume mounted read-only — no host path, "
+     "daemon-side, the estimate.go class"),
+    ("internal/stacks/undo.go", '"-v", src+":/from:ro", "-v", dst+":/to"',
+     "the undo's copy (v0.263.0): named volume -> named volume, both resolved daemon-side; no host "
+     "path is involved, so the containerized-controller stranding class cannot occur"),
+    ("internal/stacks/undo.go", '"-v", copyVol+":/c:ro"',
+     "the undo's finished-marker check (v0.263.0): a named copy volume, read-only, daemon-side"),
+    ("internal/stacks/undo.go", '"-v", copyVol+":/from:ro", "-v", vol+":/to"',
+     "the undo's restore (v0.263.0): named copy volume -> the app's named volume, daemon-side"),
     ("internal/web/handlers.go", '"compose", "down", "-v"',
      "docker compose's own --volumes flag (DR reset wipes the stack's volumes) — not a mount"),
 ]