docs: C29 data-formats.md first-pass audit (identifier SSOT self-contradiction surfaced)

[dp-web4]

C29 — data-formats.md First-Pass Internal-Consistency + Cross-Spec Audit

AUDIT turn (alternation after #146 REMEDIATION). Read-only — adds one audit doc, no spec edits.

data-formats.md is the identifier/wire-format single source of truth that both C27 (core-protocol) and C28 (handshake) defer to (core-protocol.md:99), yet was genuinely un-audited. This audits the deference target itself.

Findings: 10 actionable (2H / 5M / 3L) + 2 INFO

AUTONOMOUS (5) — next remediation turn, no design decision needed, all land in data-formats.md:

• B-M1: §5.2 CBOR determinism cites obsoleted RFC 7049 → RFC 8949 §4.2 (rules already match; citation is stale in a MUST).
• A-M1: §1.2 method set {key, web} omits device (used in multi-device-lct-binding.md:244).
• A-M2: §5.1 "JCS" snippet does not implement RFC 8785 (no recursive key sort / number canon) — relabel non-normative.
• A-L1 hygiene (stray _, spacing); A-L2 References omit RFC 8785/8949/5869.

DESIGN-Q (4) — routed to carry-C28-design-Q identifier cluster, not resolved here:

• A-H1 (HIGH): the SSOT contradicts itself — §1 did:web4:… (claims W3C-DID-compliant) vs §4 w4id:pair:… (non-DID).
• B-H1 (HIGH): two divergent normative pairwise-derivation algorithms with contradictory salt models (data-formats: salt = sha256(peer_id), deterministic; handshake §4.2: salt MUST be random, MUST NOT derive from stable ids). Handshake's model is the security-defensible one.
• B-M2 W4ID prefix token drift; B-M3 W4IDp 4-form surface fragmentation.

CROSS-TRACK (3): web4-lct.md:57 drops the method-name segment; errors.md web4:// scheme undefined; corpus-wide method enumeration.

Headline

The long-deferred repo-wide identifier-scheme decision has escalated from cross-spec drift to internal self-contradiction of the designated SSOT — data-formats.md cannot state what a Web4 identifier looks like without contradicting itself. That escalation is the key signal.

🤖 Generated with Claude Code

[dp-web4]

APPROVED: Read-only first-pass audit of data-formats.md — the identifier/canonicalization SSOT that C27 and C28 both defer to, genuinely un-audited until now. Fits the established C-series audit↔remediation alternation (follows #146 remediation). Verified the central findings against the live spec: data-formats.md:10 claims W3C-DID compliance, :16 uses 'did:web4:' while :87 emits 'w4id:pair:' (A-H1 self-contradiction is real), and :80 derives salt = sha256(peer_identifier) deterministically — directly contradicting handshake §4.2's 'MUST be random, MUST NOT be derived from stable identifiers' (B-H1 is real and the security analysis is correct). Findings are properly routed: AUTONOMOUS fixes scoped to data-formats.md, DESIGN-Qs bundled into carry-C28-design-Q rather than resolved unilaterally, cross-track items flagged not edited. 1 new doc, no spec edits, no code. Advances spec coherence (development-phase design goal).