feat: enforce PR review/merge workflow state machine gates (Closes #290)

Add fail-closed review/merge state progression helpers, pre-merge gate
requirements, blocked recovery handoff checks, and MCP assessment tool.

Closes #290

gitea_mcp_server.py

@@ -477,6 +477,7 @@ import review_proofs  # noqa: E402
 import agent_temp_artifacts
 import issue_lock_worktree  # noqa: E402
 import merged_cleanup_reconcile  # noqa: E402
+import review_merge_state_machine  # noqa: E402
 
 
 # Fail-closed exact-issue-lock file (#204): written by gitea_lock_issue,
@@ -4082,6 +4083,14 @@ _GUIDE_RULES = {
         "inventory, summarize) needs no explicit authorization. Enforced "
         "fail closed via subagent_gate.assess_subagent_delegation and "
         "validate_subagent_report (#266)."),
+    "review_merge_state_machine": (
+        "PR review/merge must follow the enforced state machine: PRECHECK → "
+        "INVENTORY → SELECT_PR → PIN_HEAD_SHA → CREATE_BRANCHES_WORKTREE → "
+        "VALIDATE → REVIEW_DECISION → APPROVE_OR_REQUEST_CHANGES → "
+        "PRE_MERGE_RECHECK → MERGE → POST_MERGE_REPORT. Failed upstream "
+        "states forbid downstream approve/merge. infra_stop and capability "
+        "blocks stop immediately. Blocked recovery handoffs must restart the "
+        "full workflow — never replay approve/merge commands (#290)."),
 }
 
 _COMMON_WORKFLOWS = [
@@ -4786,6 +4795,66 @@ def _build_runtime_task_capabilities(
     }
 
 
+@mcp.tool()
+def gitea_assess_review_merge_state_machine(
+    target_state: str | None = None,
+    state_completion: dict[str, bool] | None = None,
+    pre_merge_gates: dict[str, bool] | None = None,
+    infra_stop: bool = False,
+    capability_blocked: bool = False,
+    recovery_handoff_text: str | None = None,
+    final_report_text: str | None = None,
+) -> dict:
+    """Read-only: assess enforced PR review/merge workflow state (#290)."""
+    completion = state_completion or {}
+    blockers = review_merge_state_machine.assess_workflow_blockers(
+        infra_stop=infra_stop,
+        capability_blocked=capability_blocked,
+    )
+    result = {
+        "workflow": review_merge_state_machine.workflow_status(
+            completion,
+            infra_stop=infra_stop,
+            capability_blocked=capability_blocked,
+        ),
+        "blockers": blockers,
+        "approve": review_merge_state_machine.can_approve(
+            completion,
+            infra_stop=infra_stop,
+            capability_blocked=capability_blocked,
+        ),
+        "merge": review_merge_state_machine.can_merge(
+            completion,
+            pre_merge_gates=pre_merge_gates,
+            infra_stop=infra_stop,
+            capability_blocked=capability_blocked,
+        ),
+    }
+    if target_state:
+        result["advancement"] = review_merge_state_machine.assess_state_advancement(
+            completion,
+            target_state=target_state,
+            infra_stop=infra_stop,
+            capability_blocked=capability_blocked,
+        )
+    if recovery_handoff_text is not None:
+        result["recovery_handoff"] = (
+            review_merge_state_machine.assess_blocked_recovery_handoff(
+                recovery_handoff_text
+            )
+        )
+    if final_report_text is not None:
+        result["final_report_claims"] = (
+            review_merge_state_machine.assess_final_report_state_claims(
+                final_report_text,
+                state_completion=completion,
+                approve_completed=bool(completion.get("APPROVE_OR_REQUEST_CHANGES")),
+                merge_completed=bool(completion.get("MERGE")),
+            )
+        )
+    return result
+
+
 @mcp.tool()
 def gitea_get_runtime_context(
     remote: str = "dadeschools",