Block author mutations from reviewer MCP namespace (Issue #209)

Add role_namespace_gate to fail closed when reviewer-bound sessions attempt
author mutations (create_pr always blocked; create_issue only when profile
explicitly grants gitea.issue.create). Extend mutation audit records with
mcp_namespace, task_role, and operation fields. Add handoff parity checks in
review_proofs for author role vs reviewer namespace mismatches.

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

role_namespace_gate.py

@@ -0,0 +1,89 @@
+"""Block author mutations from reviewer-bound MCP namespaces (#209).
+
+Every mutation must prove that the active profile role, inferred MCP
+namespace, and declared task role align. Reviewer sessions cannot silently
+perform author-side work (especially PR creation).
+"""
+
+from __future__ import annotations
+
+import gitea_config
+import role_session_router
+
+
+def infer_mcp_namespace(profile_name: str | None) -> str:
+    """Map a runtime profile name to its MCP namespace label."""
+    lower = (profile_name or "").strip().lower()
+    if "reviewer" in lower and "author" not in lower:
+        return "gitea-reviewer"
+    if "author" in lower:
+        return "gitea-author"
+    return profile_name or "gitea-default"
+
+
+def derive_role_kind(allowed, forbidden=()) -> str:
+    """Classify the active profile the same way as ``mcp_server._role_kind``."""
+
+    def can(op):
+        return gitea_config.check_operation(op, allowed, forbidden)[0]
+
+    review = can("gitea.pr.approve") or can("gitea.pr.merge")
+    author = can("gitea.pr.create") or can("gitea.branch.push")
+    if review and author:
+        return "mixed"
+    if review:
+        return "reviewer"
+    if author:
+        return "author"
+    return "limited"
+
+
+def check_author_mutation_namespace(
+    mutation_task: str,
+    profile: dict,
+) -> tuple[bool, list[str]]:
+    """Return (allowed, reasons). Fail closed on reviewer/author mismatch."""
+    required_role = role_session_router.required_role_for_task(mutation_task)
+    if required_role != "author":
+        return True, []
+
+    allowed = profile.get("allowed_operations") or []
+    forbidden = profile.get("forbidden_operations") or []
+    active_role = derive_role_kind(allowed, forbidden)
+    profile_name = profile.get("profile_name") or ""
+    namespace = infer_mcp_namespace(profile_name)
+
+    if mutation_task == "create_pr":
+        if active_role == "reviewer" or namespace == "gitea-reviewer":
+            return False, [
+                "author mutation 'create_pr' blocked in reviewer MCP namespace "
+                f"({namespace}); launch gitea-author",
+            ]
+
+    if active_role == "reviewer" or namespace == "gitea-reviewer":
+        if mutation_task == "create_issue":
+            ok, _ = gitea_config.check_operation(
+                "gitea.issue.create", allowed, forbidden)
+            if ok:
+                return True, []
+        return False, [
+            f"author mutation '{mutation_task}' blocked: active session is "
+            f"reviewer-bound ({profile_name} / {namespace})",
+        ]
+
+    return True, []
+
+
+def mutation_audit_context(mutation_task: str, profile: dict, *,
+                           remote=None, repository=None) -> dict:
+    """Structured mutation metadata for audit records (#209)."""
+    allowed = profile.get("allowed_operations") or []
+    forbidden = profile.get("forbidden_operations") or []
+    return {
+        "mcp_namespace": infer_mcp_namespace(profile.get("profile_name")),
+        "profile_name": profile.get("profile_name"),
+        "task_role": role_session_router.required_role_for_task(mutation_task),
+        "operation": mutation_task,
+        "remote": remote,
+        "repository": repository,
+    }