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>

.github/rulesets/README.md

@@ -0,0 +1,26 @@
+# Merge enforcement (finding 1 — external dependency)
+
+A workflow file in `.github/workflows/` **defines** jobs; it does **not** enforce
+that they pass before merge. Enforcement is a server-side GitHub setting
+(branch protection / repository ruleset) that marks the jobs as **required
+status checks** on `main` and the merge queue. That setting lives in the GitHub
+repository configuration, not in this repository's tree, and applying it
+requires repository-admin privileges and an authenticated `gh`/API token.
+
+This is therefore BLOCKED on external infrastructure. To close the gap, a repo
+admin applies the ruleset in `main-required-checks.json`:
+
+```bash
+# Requires: gh auth login as a repo admin
+gh api -X POST repos/<owner>/<repo>/rulesets \
+  --input .github/rulesets/main-required-checks.json
+
+# Verify the required checks are active:
+gh api repos/<owner>/<repo>/rulesets --jq '.[].name'
+gh api repos/<owner>/<repo>/branches/main/protection 2>/dev/null \
+  || echo "no classic protection (rulesets in use)"
+```
+
+Until that ruleset is active, the `merge-gates` and `web-rust-gates` jobs are
+*advisory CI*, not merge enforcement. Do not treat their presence in the tree as
+satisfying the merge-blocking requirement.

.github/rulesets/main-required-checks.json

@@ -0,0 +1,27 @@
+{
+  "name": "main-merge-gates",
+  "target": "branch",
+  "enforcement": "active",
+  "conditions": { "ref_name": { "include": ["refs/heads/main"], "exclude": [] } },
+  "rules": [
+    { "type": "pull_request",
+      "parameters": {
+        "required_approving_review_count": 0,
+        "dismiss_stale_reviews_on_push": true,
+        "require_code_owner_review": false,
+        "require_last_push_approval": false,
+        "required_review_thread_resolution": false
+      }
+    },
+    { "type": "required_status_checks",
+      "parameters": {
+        "strict_required_status_checks_policy": true,
+        "required_status_checks": [
+          { "context": "merge-gates" },
+          { "context": "web-rust-gates" }
+        ]
+      }
+    },
+    { "type": "non_fast_forward" }
+  ]
+}

.github/workflows/merge-gates.yml

@@ -67,12 +67,21 @@ jobs:
       - name: Enforce required artifacts exist
         run: |
           for r in domain_participation_report causal_rank_report \
+                   causal_explanation_report \
                    compression_resistance_report metamorphic_response_report \
                    mutation_survivor_report runtime_equivalence_report \
                    replay_report coverage_report provenance_report \
                    compliance_report; do
             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; }
+
+      # Independent attestation (findings 2, 3): a SEPARATE process recomputes
+      # the Merkle root from the retained leaves and checks it against the
+      # producer's claim. It never reads compliance_report.json. A producer that
+      # reported a root inconsistent with its own leaves fails here.
+      - name: Independent attestation of evidence
+        run: cargo run --release -p attestation --bin attest -- ci_out
 
       - name: Upload acceptance evidence
         if: always()