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>

crates/world_model/src/world.rs

@@ -262,4 +262,45 @@ impl WorldDelta {
         }
         h.finish()
     }
+
+    /// Serialize the full delta to one line of whitespace-separated integers.
+    /// Round-trips [`hash`] exactly (used as attestation evidence).
+    pub fn serialize(&self) -> String {
+        let mut t: Vec<String> = vec!["delta-v1".to_string(), self.turn_advance.to_string()];
+        t.push(self.domain_deltas.len().to_string());
+        for d in &self.domain_deltas {
+            t.push(d.domain.0.to_string());
+            for &v in &d.observed {
+                t.push(v.to_string());
+            }
+            for &v in &d.hidden {
+                t.push(v.to_string());
+            }
+        }
+        t.join(" ")
+    }
+
+    /// Reconstruct a delta from [`serialize`]. Total: `None` on malformed input.
+    pub fn deserialize(s: &str) -> Option<WorldDelta> {
+        let mut it = s.split_whitespace();
+        if it.next()? != "delta-v1" {
+            return None;
+        }
+        let turn_advance: u64 = it.next()?.parse().ok()?;
+        let n: usize = it.next()?.parse().ok()?;
+        let mut domain_deltas = Vec::with_capacity(n);
+        for _ in 0..n {
+            let domain = DomainId(it.next()?.parse().ok()?);
+            let mut observed = [0i64; LANES];
+            for v in observed.iter_mut() {
+                *v = it.next()?.parse().ok()?;
+            }
+            let mut hidden = [0i64; HIDDEN_LANES];
+            for v in hidden.iter_mut() {
+                *v = it.next()?.parse().ok()?;
+            }
+            domain_deltas.push(DomainDelta { domain, observed, hidden });
+        }
+        Some(WorldDelta { domain_deltas, turn_advance })
+    }
 }