test(interop): pin read_every_path paths and scope bare-envelope README claim (LAB-8602)

[27Bslash6]

Follow-ups to #158. Tests and README only: no library change.

• README, interop section. The bare-envelope sentences ("fails only when its shape does not fit the requested type", "does read one") now say they hold for a client without encryption, and that an encrypting client fails at decrypt whatever the type.
• CK-frame sweep. every_ck_frame_in_the_file_is_refused_on_every_path now assert_eq!s the path names read_every_path returns against the five expected ones (serializer::deserialize, interop::deserialize, CacheKit::get, CacheKit::interop_get, CacheKit::interop_get_swr). Before, dropping a push from read_every_path would shrink the sweep silently; checked by removing the CacheKit::get push locally, which makes the sweep fail.
• Test docs. The EnvelopedValue comment cites default_saas_write_msgpack_bytestorage_bin's payload (the bytes the bare-envelope vector carries). The module doc mentions the positional-match assertion the bare-envelope test already makes. The read_every_path doc says "every read path of a client without encryption" and "this SDK writes".
• plain_reads_reject_a_plaintext_entry also checks that interop_get_swr returns Encryption on a plaintext entry.

cargo fmt --check, cargo clippy --all-targets -D warnings and cargo test -p cachekit-rs pass locally.

Closes LAB-8602

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📥 Commits

Reviewing files that changed from the base of the PR and between b5fb2a6 and eae0040.

📒 Files selected for processing (4)

• README.md
• crates/cachekit/tests/common/mod.rs
• crates/cachekit/tests/encryption_tests.rs
• crates/cachekit/tests/python_frame_tests.rs

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Summary by CodeRabbit

• Bug Fixes
  • Encrypted clients now consistently reject plaintext entries during decryption, including when using stale-while-revalidate reads.
• Documentation
  • Clarified how unencrypted clients read backend entries and how bare envelopes are decoded.
• Tests
  • Expanded coverage of encrypted-client plaintext rejection and confirmed that the CK-frame test exercises all five read paths.

Walkthrough

Documentation now describes bare ByteStorage envelope decoding for encrypted and unencrypted clients. Tests add an interop_get_swr encryption-error assertion and check that the CK-frame test covers five read paths.

Changes

Bare envelope read paths

Layer / File(s)	Summary
Document and check bare-envelope read paths README.md, crates/cachekit/tests/common/mod.rs, crates/cachekit/tests/encryption_tests.rs, crates/cachekit/tests/python_frame_tests.rs	The documentation clarifies encrypted-client rejection and unencrypted-client decoding. Tests check the interop_get_swr encryption error and confirm that the CK-frame test covers five read paths.

Priority: ⬇️ Low

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

Change: Other

Merge Risk: ⚪ Minimal · up to eae00

The PR clarifies documented read behavior and strengthens coverage of the affected paths; no material user-facing or operational risk is apparent.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check		The title clearly identifies the interop test changes and the README scope. It is concise and related to the main changes.
Description check		The description accurately covers the test updates, README clarification, documentation changes, and validation results.
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files. (1 skipped: 1 …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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