F-S2 + F-S3: compose-derived appdata dir resolution (v0.131.0)

The controller assumed an app's HDD appdata dir is always appdata/<stackName>.
paperless-ngx writes appdata/paperless (stack paperless-ngx), so every consumer
keying by stack name silently missed it via a stat-and-skip. One canonical
resolver appbackup.AppDataDirNames derives the real dir name(s) from the app's
compose ${HDD_PATH} binds; all consumers use it.

- F-S2 (tier-2): RunTier2 mirrors the resolved appdata/<name> (paperless docs
  got NO tier-2 copy before). Tier2Info size + RestoreTier2Files live dir use it.
  WARN when a declared appdata dir is absent. New tier2Mirror seam.
- F-S3 (migrate, NEW): all six per-app appdata legs (collision/size/copy/verify/
  cleanup/skip-set) now loop resolved names. scope="app" migration of paperless
  previously copied nothing and left an empty media dir (scope="all" was saved by
  the merge walk). WARN on missing declared dir in the copy leg.
- Multi-dir (N>1) refusal: tier-2 backup/info/restore refuse loudly (Hungarian);
  migrate supports N. No catalog app hits it today; lifted by Task 3.
- Display: storage page sums resolved dirs.
- Truth repair: the v0.130.0 "tier-2 copies the namespace wholesale" claim is
  false; corrected in CHANGELOG + main.go export-adapter comment.

+9 tests; red-proofs RP-1..RP-5 all confirmed. Controller-only, no agent/hub
coupling. Task 1 of the backup-classification-redesign arc.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A45Qop8YY8tS94bz63LFne

CONTEXT.md

@@ -7,7 +7,28 @@
 >
 > Ask Claude Code: "Please update CONTEXT.md with what we did today"
 
-Last updated: 2026-07-14 (v0.130.0 — CRITICAL C6B-F1 hollow-.fab-export fix + C6B-F2 share-removal guard)
+Last updated: 2026-07-14 (v0.131.0 — F-S2 + F-S3 compose-derived appdata dir resolution)
+
+> **2026-07-14 — v0.131.0: F-S2 + F-S3 (compose-derived appdata dir resolution).** Task 1 of the
+> backup-classification-redesign arc (spike: `felhom.eu/documentation/audits/SPIKE-backup-classification-2026-07-14.md`).
+> The controller assumed `appdata/<stackName>`; paperless-ngx writes `appdata/paperless` (stack
+> `paperless-ngx`). ONE canonical resolver `appbackup.AppDataDirNames(hddPath, stackName, mounts)`
+> derives the real dir name(s) from compose `${HDD_PATH}` binds (deduped/sorted; fallback `[stackName]`);
+> all consumers use it. **F-S2** (spike-proven): `RunTier2`/`Tier2Info`/`RestoreTier2Files` now hit the
+> resolved dir (paperless documents got NO tier-2 copy before — the appdata leg stat-skipped a dir that
+> never existed). **F-S3 (NEW, found this session):** `migrate.go` keyed all six per-app appdata legs by
+> stack name; **scope="app"** has no merge walk, so migrating paperless-ngx copied nothing, verified
+> vacuously, flipped HDD_PATH → **empty media dir** (scope="all" was saved by the merge walk — data safe,
+> accounting off). All six legs now loop resolved names. **Multi-dir (N>1) refusal** is defensive (no
+> catalog app hits it today: immich/nextcloud/romm match, paperless mismatches, each app = exactly ONE
+> dir): tier-2 backup/info/restore refuse loudly (Hungarian); **migrate supports N naturally**. This
+> limitation is **deferred to Task 3 (tier-policy engine)**, which owns the destination layout. Storage
+> page sums resolved dirs. Truth repairs: the v0.130.0 CHANGELOG/CONTEXT "tier-2 copies the namespace
+> wholesale" claim is FALSE — corrected in the v0.131.0 CHANGELOG entry + `main.go` export-adapter
+> comment; tier-2 copies the recovery unit + resolved `appdata/<name>` ONLY (NOT userdata — F-S1,
+> unaddressed here). New seam `tier2Mirror`; `migSeams.resolveNames`. +9 tests, RP-1..RP-5 all
+> confirmed. Controller-only, no agent/hub coupling. **NOT live-validated here:** scope="app" migration
+> of a real app between drives (F-S3 live proof — supervised leg, Viktor's session).
 
 > **2026-07-14 — v0.130.0: CRITICAL C6B-F1 (hollow .fab export) + C6B-F2 (share-removal guard).**
 > CAMPAIGN-6B proved `.fab` export shipped **config-only, data-free bundles** for 12/13 `needs_hdd`