Module signed_row 

On-disk wire shape for a JSONL row that participates in the Ed25519 signature chain (T-3.D.6, ADR 0010 §1-§2).

A SignedRow is the canonical envelope written one-per-line to events.jsonl. It flattens the existing cortex_core::Event fields at the top level (so legacy tools that parse Event-shaped rows still see every field they expect) and adds one new field, signature, carrying the Ed25519 RowSignature over the row’s canonical attestation preimage.

Why a wrapper instead of a new field on Event

Event lives in cortex-core and is part of the BUILD_SPEC §9.1 wire-shape contract. Extending it would ripple through every consumer crate. The wrapper keeps the change local to cortex-ledger: we own the persistence layer, so we own the on-disk envelope.

Backward compatibility on read

signature is Option<RowSignature>; an old row that pre-dates this lane (no signature field on disk) deserializes with signature: None. That is NOT a silent pass — the audit verifier flags it as crate::audit::FailureReason::MissingSignature (per ADR 0010 §1 “Single asymmetric trust domain”: rows without a valid Ed25519 signature do not verify; there is no symmetric-MAC fallback). A one-shot resign of any pre-3.D.6 fixture is required and documented in scripts/resign-jsonl.sh.

Wire shape (illustrative — exact bytes are normative in code)

{
  "id": "evt_…",
  "schema_version": 1,
  "observed_at": "2026-05-03T12:00:00.000000Z",
  "recorded_at": "2026-05-03T12:00:00.100000Z",
  "source": { "type": "user" },
  "event_type": "cortex.event.user_message.v1",
  "trace_id": null,
  "session_id": "s-001",
  "domain_tags": [],
  "payload": { "text": "hello" },
  "payload_hash": "…",
  "prev_event_hash": null,
  "event_hash": "…",
  "signature": {
    "schema_version": 1,
    "key_id": "fp:abc…",
    "signed_at": "2026-05-03T12:00:00.000000Z",
    "bytes": "<base64 64-byte ed25519 signature>"
  }
}

Structs

RowSignature

Per-row Ed25519 signature persisted alongside the Event fields.

SignedRow

On-disk envelope for one JSONL row.

Functions

b64_decode

Decode URL-safe base64 (no padding). Returns None on any invalid byte or truncated final group; the verifier treats that as crate::audit::FailureReason::BadSignature.

b64_encode

Encode bytes as URL-safe base64 (no padding). Local helper so the crate does not pull in the base64 crate for one signature field.