docs(cache-key): serializer code must be derived, and per-identity (LAB-4351)

[27Bslash6]

Serializer Code Derivation in Cache Key Specification

Overview

This change updates spec/cache-key-format.md to close an underspecified area of the cache-key suffix: the spec defined the {serializer_code} position and referenced SERIALIZER_CODES[serializer_type] in pseudocode, but never stated where serializer_type originates or what guarantees the mapping must satisfy. The revision converts that gap into explicit normative requirements and supplies a complete derivation routine.

Specification Changes

Verification baseline. The document header moves from cachekit-py v0.12.0 to v0.18.0.

Serializer code table. The table gains a Canonical name column, binding each code to the identity string the wire format records (default, auto, orjson, arrow, local). Two rows are new:

• l — reference caching / no serialization, previously shipped but undocumented.
• x + 4 hex — the derived fallback for any identity outside the table.

The {serializer_code} field description is updated accordingly: codes are 1 character for table entries and 5 characters for derived ones, so the suffix is no longer fixed-width.

Fallback derivation. Unknown identities now map to "x" plus the lowercase hex of blake2b(identity, digest_size=2). This replaces a shared bucket with a per-identity value, which is required for the non-collision rule stated alongside it.

Normative requirements added.

• The code MUST derive from the configured serializer, not a constant default. The stated failure mode is a shared keyspace across serializers, mutual eviction via the reader-side name check, and a permanent 0% hit rate.
• Identities the wire format records differently MUST NOT share a code.
• One identity MUST always produce one code, derived from the same value the wire format records — explicitly excluding process-local values such as object addresses or randomized hashes, which would break cross-process reproducibility.
• The reader-side serializer-name check is elevated from advisory to REQUIRED; at the ≈1-in-2^16 derivation collision rate it is the sole remaining separator.
• New cross-reference to encryption.md: since cache_key is an AES-256-GCM AAD input, two serializers sharing a code yield a byte-identical AAD. The spec states directly that the cipher is not a substitute for the name check.

Python SDK scoping. Alias spellings (std/standard → default, pythonic → auto) and the instance-vs-name distinction — where an instance is recorded under its class name and therefore takes a derived x code even for built-ins — are relocated into a marked Python SDK note, as neither is a cross-SDK concept.

Pseudocode

A serializer_code() function replaces the unguarded dictionary lookup, with SERIALIZER_CODES and SERIALIZER_ALIASES declared adjacently. The alias map carries a constraint comment: the same canonicalization must be applied to the serializer name the wire format records, otherwise a key and its envelope can disagree on the writing serializer. The generate_cache_key default parameter changes from "std" to "default", and the metadata-suffix comment now states the value must come from decorator/client configuration.

Compatibility

No test-vector changes. All vectors in test-vectors/cache-keys.json use serializer_type: "std", which canonicalizes to default and still yields :1s. Vectors covering the newly reachable codes require re-vendoring the sha256-pinned fixture against a merged revision of this file and follow separately. cachekit-ts and cachekit-rs use the shorter {ns}:{hash} form and are unaffected.

---

Summary

Documentation-only change to the cache key specification clarifying how the {serializer_code} suffix is derived and tightening the associated read-side requirement.

Changes

spec/cache-key-format.md

• Derived code encoding specified precisely. An identity outside the code table maps to x plus the 2-byte blake2b(utf8(identity), digest_size=2) digest rendered as exactly 4 lowercase, zero-padded hex characters (no 0x prefix), matching the args-hash encoding. A worked example (cbor → x23d5) is included, and the pseudocode now uses digest.hex() rather than a numeric hex() to prevent truncation/padding errors.
• Collision guarantee restated as probabilistic. The prior absolute "MUST NOT share a code" wording is replaced with "MUST NOT be mapped onto one code by construction," with the residual ≈1-in-2^16 collision probability stated explicitly, along with its impact: hit-rate loss only, never an incorrect value.
• Read-side serializer-name check elevated to REQUIRED on every read. Readers must compare the serializer name recorded by the storage container (Python: the s field of the CK v3 frame) against the name they would record for their own configured serializer, before decoding, and reject on mismatch. A value recording no serializer name is explicitly defined as a mismatch. SDKs offering more than one serializer identity must record the name.
• Derivation source constrained. Codes must derive from serializer configuration alone — the canonical recorded name or an SDK-defined refinement that never merges two names — and never from process-local values.
• Python SDK note revised. The standard alias is removed from SERIALIZER_ALIASES (leaving std and pythonic). Instance-based serializers are documented as taking the key identity <custom>: + bare class name (e.g. ArrowSerializer() → x2263), with a note that the <custom>: prefix cannot collide with any Python identifier.
• Test vector scope clarified. The vectors are noted as generated by cachekit-py v0.12.0 and unchanged; all use serializer_type: "std" (→ 1s), so the derived codes are not yet covered.

CHANGELOG.md

Adds an entry for LAB-4351 recording the above, the addition of the l code (reference caching) and a Canonical name column, the defect corrected by cachekit-py#311 (through v0.18.0 every auto-mode key ended in s regardless of serializer, causing mutual eviction between caches differing only in serializer), and a known divergence: that PR's read guard still exempts frames recording no serializer name. Test-vector provenance and sha256 pinning are documented.

---

Summary

Documentation-only change to the serializer-code derivation pseudocode in spec/cache-key-format.md, clarifying which parts of the algorithm are fixed by the specification and which must be supplied by each SDK.

Changes

spec/cache-key-format.md

• SERIALIZER_ALIASES is now declared SDK-supplied and defaults to an empty map, with cachekit-py's std/pythonic entries demoted to an inline example. Previously the Python-specific aliases were presented as part of the algorithm, so a non-Python SDK transcribing the block would have assigned those spellings a table code rather than the derived x code its own API implies.
• Introduces a new normalize_identity(serializer_type) hook, also SDK-supplied, that runs ahead of alias resolution and table lookup. It reduces whatever the SDK accepts as a serializer to a canonical string identity; the default implementation returns the input unchanged for names-only SDKs. This provides the documented insertion point for instance identities (<custom>: + class name), which the prior version had no place to produce because serializer_type was passed directly into a string lookup.
• serializer_code() is updated to call normalize_identity() before alias and table lookup.
• The hook is documented as the "SDK-defined refinement" permitted by the one-identity-one-code rule and is constrained to be a pure function of serializer configuration — never an object address or randomized hash.

CHANGELOG.md — corresponding entry describing the rationale and the purity constraint.

No changes to the code table, key format, or test vectors.

---

Summary

Documentation-only change clarifying how conforming SDKs must interpret the serializer_type field in the shipped cache-key test vectors.

Changes

spec/cache-key-format.md

• The Test Vectors section now states that the serializer_type: "std" value present in all 10 vectors is a cachekit-py-specific alias for the canonical default identity. An SDK that does not accept that spelling MUST read it as default rather than adding std to its own alias map.
• A CONFORMANCE note was added to the SERIALIZER_ALIASES pseudocode block, documenting the same rule and its failure mode: treating "std" as an unaliased identity yields the derived code x + blake2b("std"), which fails all 10 vectors.

CHANGELOG.md

• The existing entry on the normalize_identity() hook was extended to record this clarification and its rationale.

Impact

No normative change to the key-derivation algorithm or the test vectors themselves (test-vectors/cache-keys.json is unchanged). The change closes an ambiguity that would otherwise push SDK implementers toward polluting their alias maps with another SDK's naming in order to pass conformance.

---

Summary

Documentation-only update to spec/cache-key-format.md clarifying test-vector conformance requirements for cache key generation.

Changes

The "Test Vectors" section previously stated that only the args-hash segment must match byte-for-byte when cross-SDK implementations substitute their own module path. The text now specifies that both the args-hash segment and the trailing {ic_flag}{serializer_code} suffix must match byte-for-byte.

Impact

Tightens the documented conformance contract for SDK implementers: the serializer code portion of the key is no longer implicitly exempt from exact-match verification alongside the func: segment substitution. This aligns the spec with the requirement that the serializer code is derived rather than implementation-defined, closing an ambiguity that could otherwise permit divergent key output across SDKs.

No functional or API changes; no test vectors were modified.

---

Summary

Documentation-only change to the cache key specification clarifying two aspects of serializer code handling.

Test Vectors conformance scope

The byte-for-byte match requirement in spec/cache-key-format.md was previously unscoped, requiring both the args-hash segment and the trailing {ic_flag}{serializer_code} suffix to match. This was unsatisfiable for cachekit-ts and cachekit-rs, which implement no serializer codes, and contradicted the fixture's own note field. The requirement is now split:

• The args-hash segment MUST match byte-for-byte (unconditional).
• The {ic_flag}{serializer_code} suffix MUST match only for SDKs that implement serializer codes.

normalize_identity() contract

The hook's documented contract is tightened with two additional requirements:

• Injectivity: configurations that alter the serialized container's bytes MUST NOT normalize to the same identity (e.g. arrow+gzip and arrow+none MUST NOT both yield "arrow"). Since both the derived code and the frame tag are computed from this identity, a collapsed identity causes differently-configured serializers to self-report identical frame tags, defeating the read-side mismatch check and returning a mismatched container as a hit rather than a miss.
• Object-to-string marker: a refinement mapping a serializer object to a string MUST use a marker no bare identity can produce. This was previously presented as a cachekit-py implementation example and is now a requirement on the hook's contract.

CHANGELOG.md is updated with corresponding entries. No behavioral or API surface changes beyond the specification text.

---

This PR revises the cache-key specification and its changelog. The main change updates how the serializer code in cache keys is documented. It also marks the 7-segment key format as a Python SDK convention and documents what the backend actually enforces on keys.

Serializer code in cache keys (LAB-4351)

• Upstream fix status: references to cachekit-py#311 are updated from open @ 3fd7c35 to merged as ee65250, shipping in v0.20.0.
  • The defect window is corrected to "through v0.19.0". In that window every auto-mode key ended in s, so two caches over the same function that differed only in serializer shared a key and evicted each other.
  • The noted divergence about the read guard exempting frames with no recorded serializer name is removed.
• Python SDK note: custom-serializer identity and the recorded name both carry only the bare class name. Two classes with the same __name__, from any module or nesting level, therefore get one code and one recorded name.
  • When such serializers write different bytes and share a func: segment, the application MUST key them under different ns: namespaces. Having no namespace does not count as one.
  • A configuration or implementation changed across a deploy must use a namespace the old one never wrote.
• Pseudocode:
  • It now defines the code table and serializer_code().
  • The alias map and the normalize_identity() hook are marked as SDK-supplied.
  • The earlier conformance comment on reading "std" as default is shortened to a plain note.
• normalize_identity() contract: the rationale for the injectivity requirement is clarified.
  • The derived code comes from the identity, while the read-side check compares the recorded name, which the identity equals or refines.
  • If two configurations collapse onto one identity, they share one key and one recorded name, which defeats the mismatch check.
  • Distinct identities that share a recorded name are kept apart only by their codes; for identities outside the table, that is a 16-bit digest.

Key format scope and server requirements

• Key format: a note marks the 7-segment ns:…:func:…:args:…:{ic_flag}{serializer_code} structure as the Python SDK's internal convention, not a server contract.
• New "Server-Side Requirements" section lists the checks the backend enforces:
  • percent-encoded transport
  • a decoded length of at most 400 characters
  • the charset [a-zA-Z0-9_.:-]
  • rejection of ..
  • namespace rules for ns: and nsapi: keys
  • write-space rules: ns: keys are writable only by ck_sdk_ keys, nsapi: only by ck_api_ keys, and legacy ck_live_ keys are exempt
• Default namespace: keys with neither prefix fall into an open default write space, which any key class may write.
• Test Vectors: cache-keys.json is now declared Python-SDK-only.
  • The rule that other SDKs substitute their own module path and match the args-hash byte-for-byte is withdrawn.
  • Cross-SDK conformance moves to interop-mode.json.
  • No vector changed.

Other CHANGELOG entries (spec/doc files not in this diff)

• An interop-mode.md validator note: the deployed validator accepts interop-format keys.
• A new intent-presets.md contract (LAB-514), including a correction of the master-key minimum to 32 bytes.
• Keyring encryption conformance vectors and verifier mutation tests (LAB-687), plus status reconciliation.
• TypeScript cache.secure.wrap() now fails closed when encryption is not configured (LAB-513).

---

This PR tightens the cache-key specification for serializer identities that share a recorded name.

Summary

Previously, the spec said that distinct serializer identities sharing one recorded name are "kept apart by their codes alone." This PR states that serializer codes are not a collision-resistant separator and adds a normative requirement to cover that gap.

Changes

• spec/cache-key-format.md: In the serializer identity/alias normalization section:

  • Serializer codes are no longer described as enough to separate identities that share a recorded name.
  • For two identities outside the alias table, the derived code is a 16-bit digest, so a pair collides at roughly 1 in 2^16.
  • When such a collision happens, both the key and the recorded name match. The read-side mismatch check therefore cannot catch it, and the reader gets wrong data rather than a recoverable miss.
  • The existing hit-rate-only collision guarantee applies only to identities recorded under different names.
  • New requirement (MUST): Identities that share a recorded name but write different bytes must be keyed under different ns: namespaces. This matches the existing Python note for same-name classes.

• CHANGELOG.md: The corresponding entry now states that codes are not collision-resistant (16-bit derived digest). It also records that byte-distinct identities sharing a recorded name must use distinct ns: namespaces, consistent with the Python note.

Impact

This is a documentation and specification change only. Implementations that allow multiple serializer identities with the same recorded name must now isolate them by namespace instead of relying on the derived serializer code. No wire format or key layout changes are introduced.

---

This PR refines the cache-key specification's serializer-code rules (LAB-4351). It consolidates scattered uniqueness requirements into a single rule and tightens several edge cases. Documentation only (spec/cache-key-format.md, CHANGELOG.md); no test vectors change.

Spec changes (spec/cache-key-format.md)

• Read-side name check scope: The required pre-decode comparison of the recorded serializer name now applies explicitly to serialized entries. Reference caching (l) is exempt because it stores the object itself, not a serialized container, so there is no recorded name to compare.
• AAD statement corrected: Serializers sharing a code share only the cache_key AAD component, not the entire AAD. AAD binding fails to separate them only when they also share the format token.
• Unified uniqueness rule (new):
  • An SDK SHOULD make the serializer identity distinguish configurations that write different bytes.
  • Wherever the identity does not, such configurations MUST be keyed under different ns: namespaces; no namespace does not count as one.
  • The same ns: requirement covers distinct identities that share a recorded name, because the 16-bit derived code is not collision-resistant.
  • This replaces the stricter injectivity requirement previously placed on normalize_identity(), which is now reduced to a pure-function constraint that points to this rule.
• Python SDK note:
  • Adds the alias standard → default, alongside std and pythonic.
  • States explicitly that instances of one class with different constructor arguments share one identity.
  • Defers to the unified ns: rule instead of restating it.
• Pseudocode API changes:
  • SERIALIZER_ALIASES example adds "standard": "default".
  • serializer_code() now MUST raise an error for an empty or non-string identity instead of mapping it to a fallback code.
  • generate_cache_key(...): serializer_type becomes a required keyword-only parameter. It previously defaulted to "default".
• Header: The verification line is simplified to reference cachekit-py @ ee65250 (the #311 merge) only.

Changelog

• Reworded to reflect the items above.
• The separate normalize_identity() injectivity entry is folded into the main entry.
• The provenance note is shortened to state that no vector changed and that derived codes are not yet covered by vectors.

---

This PR is documentation-only and changes no test vectors. It tightens the serializer-code rules in the cache-key spec and routes all cross-SDK cache sharing through Interop Mode.

spec/cache-key-format.md

Serializer Codes table

• Removes the Cross-language? column.
• Removes the guidance to "always use s for cross-SDK interoperability."
• New statement: no serializer code makes auto-mode keys shareable across SDKs.

Read-side check scoped to multi-serializer SDKs

• An SDK offering more than one serializer identity MUST record the serializer name in the container of each serialized entry.
• On every read, such an SDK MUST compare that recorded name against its own before decoding. On mismatch it MUST return a miss.
• For such an SDK, an entry recording no name counts as a mismatch.
• SDKs offering a single identity (cachekit-ts, cachekit-rs) are exempt from both the recording and the comparison.
• The following fall outside both rules:
  • Interop Mode entries.
  • In-process live-object caches (in cachekit-py: reference caching l and backend=None).

New normative "Deriving the identity" paragraph
These rules previously existed only as pseudocode comments:

• Each accepted alias MUST resolve to exactly one canonical name. The key code, the recorded name and the serializer that writes the bytes MUST all correspond to that canonical name.
• When an SDK accepts a serializer object, the resulting string identity MUST carry a marker that no table name, alias or accepted name contains.
• Empty or non-string identities MUST be rejected with an error.

Python SDK note

• Accepted aliases are now std → default and pythonic → auto.
• standard is noted as present in the key generator's alias map but rejected by the cache as a serializer name.

Cross-SDK Key Generation Strategy

• Replaced. The section previously described namespace-matched keys; it now states that keys in this format are never shared across SDKs.
• Cross-language sharing uses Interop Mode exclusively.
• The RFC discrepancy warning is updated to match.

Pseudocode

• SERIALIZER_ALIASES example drops standard.
• Comments in normalize_identity() and serializer_code() now reference the normative prose instead of restating the rules.

spec/wire-format.md

• The CK v3 frame's header s table adds a row for a serializer instance's bare class name. A built-in class writes the same payload as its string name.
• The framing statement now excludes the two in-process modes that store no bytes: @cache.local (l) and backend=None.
• Clarifies that cachekit-py's L1 holds framed bytes only when it sits in front of a backend.

README.md

• The implementor Quick Start now describes auto-mode keys as SDK-specific and points cross-SDK sharing to Interop Mode.

CHANGELOG.md

• Updated to reflect all of the above.

---

This PR tightens the security reasoning in the serializer-code rules of the cache key specification (LAB-4351). It also adds changelog and wire-format documentation for several related work items.

Cache key format (spec/cache-key-format.md)

• Collision guarantee scoped to honest writers. A 16-bit derived-code collision costs hit rate only, never a wrong value, between honestly written entries.
• Recorded serializer name is not an integrity control. In the CK v3 frame, the serializer name is a plaintext header field. It is not an AAD input, so nothing authenticates it, even for encrypted entries. It offers no protection against a writer with backend write access. The text links to the Encryption AAD section and the wire-format frame header caution.
• AAD backstop statement corrected. The previous text implied AAD binding separates serializers that share a code but differ in format token. That is wrong because a reader takes format from the stored entry's metadata, not from its own serializer. The spec now states that AAD binding does not separate serializers sharing a code, whatever their format tokens, and the cipher is not a backstop for a missing name check.

Wire format (spec/wire-format.md)

This file now documents the twin_of field on the python-frame bin twin vector:

• It is an operator-owned declaration that the vector differs from default_saas_write_msgpack_bytestorage only in envelope encoding.
• verify enforces it as a hard failure.
• generate never adds or removes it and only warns on divergence.
• When the default write path legitimately changes, twin_of is dropped in the same commit as the regenerated vector. The legacy vector stays frozen as legacy-read proof.

CHANGELOG

• Updates the serializer-code entry to match the spec changes above.
• Adds entries for:
  • Encryption: a default-tenant conformance vector (LAB-4666).
  • SaaS API:
    • X-CacheKit-Fresh-For response header (LAB-557).
    • Cache-Control: no-store and Vary: Authorization on every response.
    • An effective-TTL definition.
    • No-expiry follow-ons, including GET /v1/cache/{key}/ttl returning 200 {"ttl": null}.
  • SaaS API alignment with the deployed server (LAB-677):
    • DELETE is idempotent.
    • GET /v1/cache/health response shape.
    • PATCH /v1/cache/{key}/ttl behavior.
    • Accepted auth key prefixes.
    • X-CacheKit-L1-Status is required for ck_sdk_ keys.
    • HEAD on a missing key returns 404, with the deployed server's 200 recorded as a known server deviation.
  • Test vectors: twin_of enforcement (LAB-3967) and upsert-by-name generate (LAB-1203), with the fixture sha256 change recorded.
• Minor wording edit in an existing entry ("expert-panel review" → "review").

No normative wire bytes or public API behavior change in this PR. The changes are documentation and specification clarifications.

---

Summary

This is a documentation-only change to the CacheKit Protocol Specification, touching spec/wire-format.md and CHANGELOG.md. It corrects outdated statements about which fixture version cachekit-core vendors. It also records how serializer class names map to the s field.

Changes

spec/wire-format.md: vendored-fixture coverage (LAB-1750)

• Removes the statement that cachekit-core vendors wire-format fixture 1.1.0.
• Removes the paragraph describing the resulting gap: no lz4_flex compressed-byte or xxh3-64 checksum check for width_boundary_bin16, and a list of three changes needed to re-vendor.
• Now states that cachekit-core's re-encode assertions recompute each twin's lz4_flex bytes and xxh3-64 checksum for the vectors in its vendored fixture.
• Adds a rule for anyone vendoring the fixture. Derive each *_bin twin's expected MessagePack bin marker from its decoded compressed_data length:
  • ≤255 → 0xc4
  • ≤65535 → 0xc5
  • otherwise 0xc6
• Explains why both alternatives are wrong:
  • Asserting that every twin is bin8 fails on width_boundary_bin16_bin (0xc5, 303 bytes).
  • Accepting all three widths cannot detect a non-shortest header.

spec/wire-format.md: serializer-code table

• The row for a serializer instance's bare class name now states two cases that record the same s value:
  • different classes sharing a bare name
  • differently configured instances of one class
• The row links to the ns: rule in cache-key-format.md#serializer-codes.

CHANGELOG.md

• Adds the entry "Wire format — vendored-fixture coverage note corrected (LAB-1750)", which summarizes the fixture correction above.

Notes

• No code, test vectors, or wire-format behavior change.
• The PR title refers to LAB-4351 (serializer code derived per identity). The only related change in this diff is the table note and its cross-reference; cache-key-format.md is not modified here.

Summary by CodeRabbit

• Documentation
  • Clarified canonical serializer identities, accepted aliases and derived cache-key codes, including how configured serializers affect cache reads and recorded-name checks.
  • Documented namespace separation for configurations that produce different bytes under the same identity, and explained how cache misses and wrong-data hits differ.
  • Listed exemptions for reference caching and SDKs with a single serializer identity.
  • Noted that existing test vectors use std as an alias for default and do not cover derived codes.
  • Clarified that the seven-segment key format is a Python SDK convention; cross-SDK key sharing uses interop mode.
  • Added details about Python cache storage formats and the deployed validator’s handling of interop-format keys in the default namespace.

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Walkthrough

The specifications define serializer-derived cache key codes, require configured serializer identities, and describe read-side name checks. They also document Python storage cases and direct cross-SDK key sharing to Interop Mode.

Changes

Serializer-aware cache keys

Layer / File(s)	Summary
Serializer identity and key generation spec/cache-key-format.md, CHANGELOG.md	The specification defines canonical and derived codes, identity normalisation, and a required serializer_type that supplies the key metadata code. It also describes test-vector coverage and verification references.
Serializer checks and SDK key conventions spec/cache-key-format.md, README.md, CHANGELOG.md	The specification documents recorded-name checks, namespace constraints, and Interop Mode for cross-SDK sharing. The README and changelog identify the seven-segment format as a Python SDK convention.
Python wire-storage cases spec/wire-format.md	The specification distinguishes live-object caching and backend=None from framed-byte storage. It also identifies serializer instances by bare class name and notes their built-in payload equivalence.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Other

Merge Risk: 🔵 Low · up to f5df2

This PR is a specification/documentation update. One remaining gap describes a theoretical serializer-identity collision that implementers should address with qualified identities or distinct namespaces before relying on this spec for cross-serializer safety.

Architecture Summary

Architecture risk: 🔵 Low · up to f5df2

The change affects 3 systems.

Changed systems: spec, CHANGELOG.md, README.md

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — spec (service) was modified; 2 changed files map to changed impact.
• observed — CHANGELOG.md (service) was modified; 1 changed file maps to changed impact.
• observed — README.md (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in README.md: The Quick Start replaces the requirement for matching keys across SDKs with the distinction that auto-mode keys are SDK-specific (with the seven-segment format identified as Python’s convention), while cross-SDK key sharing uses interop mode.
• observed — Modified behavior in spec/cache-key-format.md: The verification reference changes from cachekit-py v0.12.0 to the upstream serializer-code derivation change.
• observed — Modified behavior in spec/cache-key-format.md: The serializer-code segment is documented as one character for canonical table entries or x plus four lowercase hexadecimal characters for other identities, derived from a two-byte Blake2b digest. The table adds canonical names and the local code.
• observed — Modified behavior in spec/cache-key-format.md: The requirements specify deriving codes from configured serializer identities, recording and checking serializer names for serialized entries, and rejecting missing or mismatched names; reference caching and single-identity SDKs are exempt. They distinguish hit-rate misses for collisions between differently recorded identities from wrong-data hits when identities share a recorded name, and require different namespaces for configurations that write different bytes but share an identity or recorded name.

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Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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In `@spec/cache-key-format.md`:
- Around line 60-62: Update the fallback identity-code specification around the
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either define deterministic collision handling, enlarge the identity component
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- Line 9: Align the cache-key vector provenance between the version metadata in
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🟡 Minor · Qualify the built-in serializer equivalence. · wire-format.md:548

spec/wire-format.md:548
🗄️ Data Integrity & Integration | 🟡 Minor | ⚡ Quick win

Qualify the built-in serializer equivalence.

The row applies to every built-in serializer instance, but the cache-key specification states that same-class instances can share one identity and recorded name even when constructor settings produce different bytes. Such configurations require separate ns: namespaces. Limit this statement to default or byte-equivalent configurations.

Suggested fix

-| A serializer instance's bare class name (`StandardSerializer`, `ArrowSerializer`, a custom class) | That serializer's own output; a built-in class writes the same payload as its string name above |
+| A serializer instance's bare class name (`StandardSerializer`, `ArrowSerializer`, a custom class) | That serializer's own output; a built-in instance writes the same payload as its string name above only when its configuration is byte-equivalent |

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Review comment at @spec/wire-format.md at line 548:
Qualify the built-in equivalence in the serializer cache-key table: update the
row describing a serializer instance’s bare class name so it says its output
matches the string-name payload only for default or otherwise byte-equivalent
configurations. Keep the statement that each serializer produces its own output.

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Outside diff comments:
Review comments at @spec/wire-format.md:
- Line 548: Qualify the built-in equivalence in the serializer cache-key table:
update the row describing a serializer instance’s bare class name so it says its
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• Definition of Done / Standards: include `@file:DOD.md` or `@file:CONTRIBUTING.md` if your repo has them.
• Design System Source of Truth: include `@file:ui/index.ts` (replace with your DS entrypoint path).
• Feature Flags: include the flag key/name and `@file:flags.ts` / `@file:config.json` (and optionally the PostHog flag name).
• Edge/CDN Rules: link the Cloudflare rule/zone or describe the intended redirect/header behavior.
• Attach an MCP tool output: use `@mcp<provider|tool>` (replace with an installed MCP provider + tool, e.g., `@mcp<sentry|events.search>`).

Current Kody Configuration

Review Options

The following review options are enabled or disabled:

Options	Enabled
Bug	✅
Performance	✅
Security	✅
Business Logic	✅

Access your configuration settings here.