test(e2e): backup → fresh-instance restore full-fidelity drill

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What this is

The data-safety proof needed before 1.0. A new e2e spec,
apps/openbucket-backend-e2e/src/backup-restore-fidelity.e2e-spec.ts, that
answers the real "will my data survive an upgrade" question.

The existing backup-restore.e2e-spec.ts restores WITHIN one running instance
and checks only object keys + bytes. This drill instead:

1. Populates instance A with rich state (versioned bucket with 3 versions of
   a key; an object with user-metadata + tags + explicit Content-Type; an
   at-rest-encrypted object; a bucket with lifecycle + CORS + policy config).
2. Takes a whole-instance backup .zip.
3. Spawns a FRESH instance B — new DATA_DIR, fresh migrations, a
   different generated SSE key (asserted != A's), same root creds + admin.
4. Restores the backup into B.
5. Asserts rich fidelity on B, per dimension.

Uses the real spawn harness (two instances, ports 9280/9281) — no mocks.

What actually survived vs. the gaps found

SURVIVES (faithfully round-trips into B):

• Current object bytes — byte-exact (doc.txt, rich.json, secret.bin).
• Content-Type (S3 HEAD).
• User-metadata — carried by the manifest, re-applied on restore, present on B's
  row (asserted via the admin metadata endpoint; see caveat below).
• Object tags (S3 GET ?tagging).
• Bucket versioning status (Enabled).
• At-rest SSE round-trip across DIFFERENT instance keys — the backup stores
  DECRYPTED bytes, so B serves the original plaintext even though B generated its
  own SSE key. The bytes are not lost when the instance key changes.

GAPS — asserted as ACTUAL (lossy) behavior; candidate 1.0 data-loss surfaces:

• Prior object versions are DROPPED. A had 3 versions of doc.txt; only the
  current pointer row is backed up (objectRepo.listByPrefix), so B has exactly
  1. Version history does not survive backup/restore.
• GET ?versionId is ignored on read (unsupported) — even on A there is no
  way to fetch an old version's bytes over the wire.
• Per-bucket default-encryption config is DROPPED. B's bucket has no default
  encryption after restore (404), and because the writer keys off that
  now-missing config, the restored blob is written PLAINTEXT on B — the
  at-rest-encryption property is lost even though the bytes survive.
• Bucket lifecycle, CORS, and policy are DROPPED (all 404 on B). The manifest
  never captures them, though they live on the same bucket row.

Incidental pre-existing bug (NOT a backup defect), pinned by its own test:
S3 HEAD never emits x-amz-meta-* response headers, even for a freshly-written
object — the metadata IS stored (DB) and IS returned by the admin metadata
endpoint. Reproduces on both A and B, so it is a property of the S3 HEAD response
path, not of restore. User-metadata fidelity is therefore asserted through the
admin endpoint, and the HEAD omission has a clearly-labelled caveat test so a
future fix trips it.

Verification

• npx nx build openbucket-backend
• New spec: 14/14 pass, run 3× with no flakes; no leftover listeners on
  9280/9281 after teardown.
• Full e2e suite: 38 suites passed (1 pre-existing skip), 189 tests, no
  regressions.
• nx lint openbucket-backend-e2e: 0 errors for the new file.

🤖 Generated with Claude Code