docs: fix stale rustdoc claims — phantom CACHEKIT_NAMESPACE, self-heal overstatement (LAB-682)

[27Bslash6]

Closes LAB-682. Doc-truth fix: three rustdoc surfaces in this repo claimed behaviour the code does not have (trust-bug class per LAB-388; the docs-site pages were already fixed in cachekit-io/docs#10, this PR fixes the source comments).

Changes

1. CACHEKIT_NAMESPACE phantom env var removed — CachekitConfig::from_env reads only CACHEKIT_API_KEY / API_URL / MASTER_KEY / PREVIOUS_MASTER_KEYS / DEFAULT_TTL; nothing reads CACHEKIT_NAMESPACE. Removed from:
   • crates/cachekit/src/client.rs — interop_get rustdoc # Errors section
   • crates/cachekit/src/client.rs — reject_namespaced_interop error-message string (explicitly required by the issue AC; the only non-comment line touched — message content only, no logic change, and interop_get_fails_closed_on_namespaced_client asserts on the Config variant, not the text)
   • crates/cachekit-macros/src/lib.rs — #[cachekit] macro rustdoc
   • README.md — interop callout (same lie, found by grep during implementation)
2. Self-heal claim scoped (crates/cachekit-macros/src/lib.rs) — "treated as a miss and overwritten (self-healing), never an error loop" now states what the generated code does: only CachekitError::Serialization self-heals; on secure functions an AES-GCM auth failure raises CachekitError::Encryption, which propagates (fail-closed) until expiry. Wording matches cachekit-io/docs#10.
3. 16-byte key minimum — already fixed on main (encryption_from_bytes rustdoc says ≥ 32 bytes, matching EncryptionLayer::new); nothing to change.

Verification

• cargo fmt --all --check clean; cargo clippy clean (pre-commit hooks).
• cargo doc --no-deps --workspace builds; the two remaining rustdoc warnings are pre-existing unresolved intra-doc links on untouched lines.
• cargo test --workspace — all green (169 tests + doc-tests, 0 failures).
• No runtime behaviour changes; git diff is doc comments + README + the one error-message string the AC calls out.

Summary by CodeRabbit

• Documentation
  • Clarified interoperation guidance: clients must omit the .namespace() setting.
  • Updated configuration guidance to remove references to CACHEKIT_NAMESPACE.
  • Documented the distinction between deserialisation misses and AES-GCM authentication failures.
  • Clarified that secure authentication errors persist until the affected entry expires or is deleted.

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📥 Commits

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📒 Files selected for processing (3)

• README.md
• crates/cachekit-macros/src/lib.rs
• crates/cachekit/src/client.rs

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Walkthrough

The change updates interop-mode documentation and its namespace configuration error message. It removes CACHEKIT_NAMESPACE references, requires clients to omit .namespace(), and documents distinct handling for deserialisation misses and AES-GCM authentication failures.

Changes

Interop documentation

Layer / File(s)	Summary
Align interop guidance and error behaviour README.md, crates/cachekit-macros/src/lib.rs, crates/cachekit/src/client.rs	Interop guidance now refers to the client’s .namespace() setting. Macro documentation distinguishes deserialisation misses from AES-GCM authentication failures and documents their handling. The namespace rejection error message uses the same guidance.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: kodus-27b

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarises the documentation fixes for the obsolete CACHEKIT_NAMESPACE reference and the self-healing claim.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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