Finding 4: full-trace evidence — reconstructed and re-derived, not summarized

Removes the deferral. Each sampled execution's FULL trace (every graph edge,
count, weight) and delta are persisted as evidence; the independent attestor
reconstructs them, recomputes the canonical trace hash and delta hash, re-derives
the replay-record leaf, and confirms it is among the retained Merkle leaves the
root is built from. The behavior-fingerprint hash is re-derived from features
(not trusted), and f64 divergence is stored bit-exact for an identical hash.

- trace_model: ExecutionTrace::serialize/deserialize (round-trips canonical_hash;
  total on garbage). Test: full_trace_serialize_roundtrips_canonical_hash.
- world_model: WorldDelta::serialize/deserialize (round-trips hash).
- ci_reports: retains TRACE_EVIDENCE_SAMPLE full traces; writes
  evidence/traces.tsv.
- attestation: depends on trace_model/world_model; reconstructs each trace,
  recomputes the leaf, requires it to match the claimed leaf AND be a retained
  leaf. Negative control: tampered_trace_breaks_attestation (corrupting the full
  trace, leaving the claimed leaf, fails attestation).
- merge-gates: requires evidence/traces.tsv; the separate attest step verifies it.

End-to-end (fast profile): 256/256 full traces reconstructed and re-derived to
retained leaves; recomputed root matches the claim over 6600 leaves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/merge-gates.yml

@@ -75,6 +75,7 @@ jobs:
             test -s "ci_out/${r}.json" || { echo "MISSING ARTIFACT: ${r}.json"; exit 1; }
           done
           test -s ci_out/evidence/leaves.tsv || { echo "MISSING EVIDENCE: leaves.tsv"; exit 1; }
+          test -s ci_out/evidence/traces.tsv || { echo "MISSING EVIDENCE: traces.tsv"; exit 1; }
 
       # Independent attestation (findings 2, 3): a SEPARATE process recomputes
       # the Merkle root from the retained leaves and checks it against the