fix(mcp): role-exclusive capability invariants and structured fail-closed submit (Closes #723)

Defect A - invariants:
- task_capability_map.ROLE_EXCLUSIVE_TASKS is now the single shared
  definition of role-exclusive tasks; the resolver's inline copy is gone
  (AC1/AC5 drift surface removed).
- tests: every role-exclusive task must exist in the capability map;
  formal-review tasks stay role-exclusive; canonical merger satisfies
  merge_pr; canonical reconciler satisfies branch-cleanup tasks
  (extends the #722 break-glass invariant suite).

Defect B - unactionable internal_error:
- AC3: gitea_resolve_task_capability records the capability purity
  baseline first but stamps _preflight_resolved_role/_task only for an
  ALLOWED resolve; a denied resolve clears any stale stamp
  (_clear_resolved_capability_stamp) so later mutation preflights key
  off the real profile role.
- AC4: _evaluate_pr_review_submission converts
  _verify_role_mutation_workspace failures (role binding, stale
  runtime) into result reasons with blocker_kind=workspace_role_binding
  instead of letting RuntimeError escape as a generic internal_error.
- AC5: _build_runtime_task_capabilities applies the resolver's
  role-exclusive filter when given the active role kind and labels each
  entry role_filtered/permission_only; matching_configured_profiles
  honors declared profile roles for role-exclusive tasks.

Validation: focused suites 22 passed (+48 subtests); adjacent resolver/
runtime/review suites 72 passed; full suite 2929 passed, 6 skipped,
221 subtests (single pre-existing Starlette warning, #682).

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

task_capability_map.py

@@ -330,6 +330,32 @@ TASK_CAPABILITY_MAP: dict[str, dict[str, str]] = {
     },
 }
 
+# #723 AC1/AC5: tasks where permission alone is NOT enough — the profile's
+# role kind must also match. Shared by ``gitea_resolve_task_capability`` and
+# the runtime-context capability report so the two can never disagree about
+# which tasks are role-exclusive (incident #722: runtime context said
+# review_pr was allowed while the resolver fail-closed the same session).
+ROLE_EXCLUSIVE_TASKS: frozenset[str] = frozenset({
+    "review_pr",
+    "approve_pr",
+    "request_changes_pr",
+    "blind_pr_queue_review",
+    "pr_queue_cleanup",
+    "pr-queue-cleanup",
+    "merge_pr",
+    "create_branch",
+    "push_branch",
+    "create_pr",
+    "commit_files",
+    "gitea_commit_files",
+    "address_pr_change_requests",
+    "delete_branch",
+    "cleanup_merged_pr_branch",
+    "reconciliation_cleanup",
+    "work_issue",
+    "work-issue",
+})
+
 # Issue-mutating MCP tools and their resolver task keys.
 ISSUE_MUTATION_TOOL_TASKS: dict[str, str] = {
     "gitea_create_issue": "create_issue",