Ratify the byte-level identity procedure — JCS (RFC 8785) canonical form + SHA-256, operation_id concatenation, key derivation

Context

RFC-001 §1 pins the byte-level identity procedure and states that implementing it requires a short ADR ratifying items 1–4 (master doc §12.5: identity rules are invariant-affecting). ADR-0013 supplied the encoder/hash pins (rfc8785 0.1.4, version-pinned and vendor-ready; stdlib hashlib.sha256) and the cross-implementation evidence: four independent JCS implementations (Python/Node/Go/Rust) produced byte-identical canonical output on all shared vectors, including the RFC 8785 number/string torture vector and a non-ASCII key-sorting vector [VF] (T-000 spike, recorded in ADR-0013). T-101 implements the procedure in src/detent/identity/.

Decision

Ratify RFC-001 §1 items 1–4 exactly as written, as the implemented contract:

1. Canonical form: the identity tuple is encoded as the JSON object {"effect_type": …, "scope": …, "stable_ids": {…}} and canonicalized per RFC 8785 (JCS) — lexicographic member ordering, canonical number/string encoding, UTF-8 bytes.
2. Normalization: stable-id values are opaque strings, hashed exactly as supplied (no case folding); absent optional members are omitted, never null.
3. Hash: intent_id = lowercase-hex SHA-256 over the canonical UTF-8 bytes.
4. operation_id = intent_id ‖ ":" ‖ step, step allocated by the ledger (RFC-002 §1 refinement of “workflow-assigned”); idempotency evidence derives only from operation_id.

Implementation pins: rfc8785==0.1.4 (exact pin, not a floor), guarded by the committed cross-implementation conformance vectors in tests/identity/vectors/ (the four T-000 spike vectors with their cross-language SHA-256 digests as the external oracle). Any vector failure is a stop-and-ask event, never a re-pin in place (T-101 human-review trigger).

Alternatives

• Naive string concatenation of tuple members — rejected: separator-injection collisions ({"a":"b:c"} vs {"a:b":"c"}); property-tested against.
• json.dumps(sort_keys=True) as canonical form — rejected: not JCS-conformant on number/string edge cases; no cross-language byte agreement.
• Hash of full contract including parameters — rejected long ago (ADR-001): breaks under re-synthesis; parameters is a carrier, never an identity input (ADR-0019).

Consequences

Every ledger record keys off this procedure; changing it re-keys the ledger (the least reversible decision in the slice). The M3 conformance tests (master doc §12.1 row 1) — permutation invariance, model-output independence, sensitivity, cross-process determinism, pinned vectors — enforce it continuously.

Risks

rfc8785 is a near-dormant micro-library (ADR-0013 negative finding 1); the frozen spec, exact pin, conformance vectors, and vendor-readiness (Apache-2.0) bound the risk. A silent encoder regression is caught by the vectors before any identity is mis-derived.

Reopen trigger

Any committed conformance vector fails to reproduce byte-for-byte under the pinned encoder; or a destination requires an identity input the three-member tuple cannot carry (would also reopen ADR-001).