Compliance hardening: enforce measured behavior, real gates, retained evidence

Addresses the attached findings as blocking compliance failures. Each fix
removes a substitution pattern and adds a negative-control test.

Finding 9 (hash changes != enforced metamorphic expectations):
  ci_reports now enforces a sound metamorphic relation per perturbation — a
  perturbation the program CONSUMES must alter the trace — grounded in
  reachability, with a non-vacuity check. Test:
  consumed_perturbation_must_alter_trace.

Finding 10 (trace counts != causal explanation):
  New causal_explanation gate ablates each recorded causal edge's source lane
  and requires the destination delta to change. Measured: true-source 0.77 vs
  scrambled-source 0.03. Threshold 0.50. New required report
  causal_explanation_report. Test:
  causal_edges_are_intervention_confirmed_not_counted.

Finding 6 (static seed corpus != failure retention):
  replay_corpus::retention adds a committed, append-only counterexample corpus
  (retained_failures.tsv) re-verified every run against the independent runtime.
  Negative control: reintroduced_bug_is_caught_by_retention.

Finding 5 (mini mutation evaluator != real acceptance gate):
  Mutants are now killed by ci_reports' OWN acceptance-gate predicates with
  single-sourced thresholds (TRACE_EDGES_MIN, etc.); evaluate_mutants replaces
  semantic_mutation::run_suite on the acceptance path. Test:
  mutants_killed_by_real_acceptance_gates.

Findings 2 & 3 (generated report != independent attestation; merkle root !=
provenance without leaves):
  ci_reports persists every Merkle leaf (evidence/leaves.tsv) + claims. New
  `attestation` crate + `attest` binary recompute the root from the leaves in a
  SEPARATE process that never reads compliance_report.json; wired as a distinct
  merge-gates step. Negative control: tampered_leaf_breaks_attestation.

Finding 8 (structural indicators != measured behavior):
  Domain gate already requires measured influence/mutation/removal; added an
  explicit reject for "appears structurally but no measured influence".

Finding 1 (workflow != merge enforcement): BLOCKED on server-side branch
  protection. Added .github/rulesets/main-required-checks.json + apply command;
  enforcement still requires a repo admin to activate the ruleset.

Finding 7 (protocol socket E2E != rendered browser E2E): BLOCKED on a CI browser
  runner; rendered-browser E2E remains advisory-only.

Finding 4 (trace summary != full trace evidence): PARTIAL. Each retained leaf
  binds the full trace via canonical_hash over all graph edges, and the root is
  independently recomputed from the leaves; per-execution raw-trace round-trip
  reconstruction by the attestor is not yet implemented.

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

Cargo.toml

@@ -11,6 +11,7 @@ members = [
     "crates/semantic_mutation",
     "crates/replay_corpus",
     "crates/ci_reports",
+    "crates/attestation",
     "crates/protocol",
     "crates/game_runtime",
     "crates/web_assets",