Support GnuPG AEAD password entries

crates/storage/tests/fixtures/compatibility/README.md

@@ -22,6 +22,14 @@ secrets. The generator reuses the checked-in identities and produces:
 - valid loose-object Git repository templates, including an automatic-commit
   history and nested-repository boundaries.
 
+`gnupg-aead/` is a separate, non-generated compatibility case. Its synthetic
+Alice entry was encrypted by GnuPG 2.4.8 with AES-256 and `--force-ocb`, yielding
+GnuPG AEAD packet type 20 addressed to Alice's encryption subkey. The directory
+contains the exact producer profile and ciphertext digest, a normal
+password-store tree, and the expected plaintext. It deliberately lives outside
+the reproducible generator's `stores/`, `expected/`, and `repositories/`
+directories so a refresh cannot silently replace genuine GnuPG producer output.
+
 Rust tests parse keys, verify signatures, decrypt every entry, compare exact
 plaintext bytes, validate ciphertext digests, validate Git objects and refs,
 and materialize isolated stores and repositories. They never invoke `pass`,
@@ -43,6 +51,11 @@ then make that rotation intentionally non-reproducible. Review all binary
 changes and the generated fingerprints, digests, and Git object IDs before
 committing them.
 
+When rotating the checked-in synthetic identities, regenerate the packet-20
+case explicitly with the producer profile in `gnupg-aead/fixture.toml`, update
+both recorded fingerprints and the digest, and independently inspect it with
+GnuPG's packet listing before review.
+
 An optional developer interoperability audit may import the generated keys
 into a disposable GnuPG home, decrypt the `.gpg` entries, and point an
 upstream `pass` 1.7.4 checkout at a materialized store. That audit is never a