feat(reviewer): require trust-gate proof in empty-queue reports (#198)

Add assess_empty_queue_report to block empty-queue claims without
pr_inventory_trust_gate.status == trusted_empty, reject weak merge-commit
corroboration, extend inventory handoff fields, and wire the gate into
build_final_report and capability-stop terminal validation.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_review_proofs.py

@@ -27,6 +27,7 @@ from review_proofs import (  # noqa: E402
     assess_controller_handoff,
     assess_inventory_completeness,
     assess_reviewer_queue_inventory,
+    assess_empty_queue_report,
     assess_live_state_recheck,
     assess_review_mutation_final_report,
     assess_role_boundary,
@@ -1020,6 +1021,10 @@ class TestControllerHandoff(unittest.TestCase):
         complete = self.BASE_HANDOFF + "\n" + "\n".join([
             "- Repositories checked: Gitea-Tools, mcp-control-plane",
             "- Open PR counts: 2 / 0",
+            "- PR inventory trust gate: trusted_nonempty / trusted_empty",
+            "- Trust gate reasons: none",
+            "- Trust gate corroborated: true",
+            "- Inventory profile: prgs-reviewer",
             "- Selected PR or reason: none eligible (self-authored)",
             "- Inventory completeness: complete, no pagination needed",
         ])
@@ -1280,6 +1285,89 @@ class TestAssessReviewerQueueInventory(unittest.TestCase):
         self.assertEqual(result["trust_gates"], {})
 
 
+class TestAssessEmptyQueueReport(unittest.TestCase):
+    """Issue #198: empty-queue reports require formal trust-gate proof."""
+
+    def _trusted_report(self, **extra):
+        lines = [
+            "Queue inventory complete.",
+            "Repository: Scaled-Tech-Consulting/Gitea-Tools",
+            "Open PR count: 0",
+            "pr_inventory_trust_gate.status: trusted_empty",
+            "pr_inventory_trust_gate.corroborated: true",
+            "Inventory profile: prgs-reviewer",
+            "Workflow correctly stops with nothing to review.",
+        ]
+        lines.extend(extra)
+        return "\n".join(lines)
+
+    def test_non_empty_report_not_claimed(self):
+        result = assess_empty_queue_report("Reviewed PR #236 and merged.")
+        self.assertFalse(result["claimed"])
+        self.assertTrue(result["proven"])
+
+    def test_empty_claim_without_trust_gate_blocked(self):
+        report = (
+            "Open PR count: 0\n"
+            "Pagination complete: yes\n"
+            "Queue cleared."
+        )
+        result = assess_empty_queue_report(report)
+        self.assertTrue(result["claimed"])
+        self.assertFalse(result["proven"])
+        self.assertTrue(result["block"])
+
+    def test_trusted_empty_report_with_required_fields_passes(self):
+        result = assess_empty_queue_report(self._trusted_report())
+        self.assertTrue(result["proven"])
+
+    def test_weak_merge_commit_corroboration_blocked(self):
+        report = (
+            "Open PR count: 0\n"
+            "Master latest commit is merge of PR #79 so queue is empty."
+        )
+        result = assess_empty_queue_report(report)
+        self.assertFalse(result["proven"])
+        self.assertTrue(
+            any("weak corroboration" in r for r in result["reasons"])
+        )
+
+    def test_author_session_reviewer_queue_wording_blocked(self):
+        result = assess_empty_queue_report(
+            self._trusted_report(),
+            task_role="author",
+        )
+        self.assertFalse(result["proven"])
+
+    def test_build_final_report_downgrades_weak_empty_queue(self):
+        final = build_final_report(
+            checkout_proof=_good_checkout(),
+            inventory=_good_inventory(),
+            validation=_good_validation(),
+            contamination=_good_contamination(),
+            identity_eligible=True,
+            merge_performed=False,
+            issue_status_verified=True,
+            capability_evidence=_good_capability_evidence(),
+            sweep=_good_sweep(),
+            live_state=_good_live_state(),
+            role_boundary=_good_role_boundary(),
+            review_mutation=_good_review_mutation(),
+            controller_handoff=_good_handoff(),
+            capability_proof=_good_capability_proof(),
+            sweep_proof=_good_secret_sweep(),
+            worktree_proof={
+                "worktree_path": "/repo/branches/review-pr-1",
+                "porcelain_status": "",
+                "scratch_used": True,
+                "scratch_path": "/repo/branches/review-pr-1",
+            },
+            report_text="Open PR count: 0. Queue cleared.",
+        )
+        self.assertNotEqual(final["grade"], "A")
+        self.assertFalse(final["empty_queue_trust_gate_proven"])
+
+
 class TestCapabilityEvidence(unittest.TestCase):
     """#179 gap 1: capability claims need exact evidence."""