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ruv a3478ea3b5 cog-ha-matter (ADR-116 P4): witness JSONL persistence
Third P4 sub-unit: serialize/parse for the witness hash chain so
audit bundles can be written to disk and replayed.

Wire shape (one record per line, alphabetical field order locked):

  {"kind":"...","payload_hex":"...","prev_hash":"...","seq":N,
   "this_hash":"...","timestamp_unix_s":N}

Why alphabetical field order: auditors archive whole bundles and
hash them. A rebuild that reordered fields would silently
invalidate every archival hash — locking the order is what makes
the JSONL stable across compiler / serde-json upgrades.

Why hex everywhere: human-greppable, monospace-friendly, no base64
ambiguity, no Vec<u8> JSON-array ugliness. Same convention as
ADR-101's `binary_sha256`.

Critically, `from_jsonl_line` RE-VERIFIES `this_hash` against
the canonical bytes derived from the parsed fields. A tampered
bundle fires `WitnessParseError::HashMismatch` BEFORE the event
loads — the parser is itself an auditor.

New surfaces:
  * `WitnessHash::from_hex` (with structured length/parse errors)
  * `WitnessEvent::to_jsonl_line`, `from_jsonl_line`
  * `WitnessParseError` enum: Json | MissingField | WrongType |
    HashLength | HashHex | PayloadHex | PayloadLength | HashMismatch
  * private `hex_encode` / `hex_decode` helpers (no `hex` crate dep)

10 new tests:
  * jsonl round-trip preserves all fields
  * jsonl line has no embedded \n / \r (one record per line)
  * jsonl field order is alphabetical (byte-stable archival)
  * parser rejects tampered payload via HashMismatch
  * parser rejects non-hex characters in hash
  * parser rejects missing field
  * hex encode/decode round-trip across empty / single byte / 0xff /
    UTF-8 / arbitrary bytes
  * hex decode rejects odd-length input
  * WitnessHash::from_hex round-trip
  * WitnessHash::from_hex rejects wrong length

44/44 cog tests green (34 → 44).

ADR-116 P4 row enumerates 4 sub-units now:  mDNS record-builder,
 witness chain primitive,  witness JSONL persistence,
 responder + embedded broker + Ed25519 signing.

Co-Authored-By: claude-flow <ruv@ruv.net>
2026-05-23 18:12:59 -04:00
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