[armagankaratosun]

What changed

release create --archive writes a full ZIP, then incremental backups that hold only what changed since the previous release. --retain-versions records S3 VersionIds instead. release verify checks both, and archive restore applies the backup chain. Archive code now lives in core/archive/.

Why

Closes #135.

Affected behavior

• User / CLI: new --archive, --archive-full, --retain-versions and release verify --sample. archive create without --overwrite now needs hard links.
• Plugin authors: ReleaseRecord gains an optional retention field.
• Operators / production: N/A
• Stored formats or control-plane state: new inventory manifests, a retention key on the release record, a marker inside each ZIP.

Type of change

• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (CLI flags, plugin contract, config, or stored format)
• Documentation
• CI / build / chore

Checks run

• uv run ruff check .
• uv run ruff format --check .
• uv run pyright
• uv run --with bandit bandit -c pyproject.toml -r src scripts -lll
• uv run pytest --strict-deps -m "not slow and not s3 and not docs_static and not snapshot and not race" -q
• Docs build (if docs changed): uv run mkdocs build --strict

Follow-up work

• Run the --retain-versions tests against a real Ceph RGW (S3-compatible store).
• Add a fallback for archive create on filesystems without hard links.
• Open a release as a Zarr store without restoring it (not part of [REQUEST] firecube release: retain and restore the chunk bytes of a release #135; deferred to v0.2.x).

Contributor certification

• Commits are signed off (git commit -s) with my real name and a reachable email.
• No credentials, generated products, caches, or virtualenvs are included in this PR.
• If AI assistance materially shaped this change, I disclosed it here and added an Assisted-by trailer.