feat(gateway): restore Gate Set C exit-time guards

Choreographer.i_am_idle now refuses with INVALID_STATE when the caller
has any pending (assigned but never claimed) task. Pre-gateway this
was implicit because the orchestrator's auto-respawn would re-spawn
the agent for the assignment, leading to a tight respawn loop. The
explicit refusal lets the agent fix the state via i_will_work_on
(dev/qa/doc) or i_will_plan (pm) first.

Existing auto-pause for in_progress tasks is preserved (Gate Set C
spec calls this out as still required) — it runs AFTER the pending
guard, so an agent with a mix of pending+in_progress is told about
the pending task first instead of silently pausing in_progress and
then looping on the pending one.

Pre-gateway reference: roboco/runtime/orchestrator.py
auto-respawn loop guards (already preserved at HEAD); the explicit
agent-facing gate is new.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

roboco/services/gateway/choreographer.py

@@ -480,10 +480,18 @@ class Choreographer:
     async def i_am_idle(self, agent_id: UUID) -> Envelope:
         """Report no more work. Soft-block if there are unread A2As or @mentions.
 
-        Before marking the agent idle, auto-pause every in_progress task this
-        agent owns so the orchestrator's PM-closure dispatcher can wake them
-        when subtasks finish, instead of leaving the parent stuck at
-        ``in_progress`` forever.
+        Before marking the agent idle:
+
+        1. Bail with ``idle_with_unread`` when context_briefing has unread A2A
+           or @mentions (must address those first).
+        2. Refuse with INVALID_STATE if the agent has any pending tasks
+           assigned but never claimed — they must call i_will_work_on (dev/qa/
+           doc) or i_will_plan (pm) first. (Gate Set C, pre-gateway implicit
+           via the orchestrator's auto-respawn.)
+        3. Auto-pause every in_progress task this agent owns so the
+           orchestrator's PM-closure dispatcher can wake them when subtasks
+           finish, instead of leaving the parent stuck at ``in_progress``
+           forever.
         """
         briefing = await self._briefing_for(agent_id, None)
         if briefing.get("unread_a2a") or briefing.get("unread_mentions"):
@@ -496,6 +504,8 @@ class Choreographer:
                 ),
                 context_briefing=briefing,
             )
+        if guard := await self._pending_assignment_guard(agent_id, briefing):
+            return guard
         await self._auto_pause_in_progress_tasks(agent_id)
         await self.task.mark_agent_idle(agent_id)
         return Envelope.ok(
@@ -505,6 +515,37 @@ class Choreographer:
             context_briefing=briefing,
         )
 
+    async def _pending_assignment_guard(
+        self, agent_id: UUID, briefing: dict[str, Any]
+    ) -> Envelope | None:
+        """Refuse i_am_idle when caller owns any pending (unclaimed) task.
+
+        Pre-gateway: the orchestrator would respawn the agent after
+        i_am_idle if they still owned pending work, leading to a tight
+        respawn loop. Now an explicit refusal lets the agent fix it via
+        i_will_work_on or i_will_plan before exiting.
+        """
+        assigned = await self.task.list_assigned_for_agent(agent_id)
+        pending = [t for t in assigned if str(t.status) == "pending"]
+        if not pending:
+            return None
+        first = pending[0]
+        agent = await self.task.agent_for(agent_id)
+        verb = "i_will_plan" if agent and agent.role in ("cell_pm", "main_pm") else (
+            "i_will_work_on"
+        )
+        return Envelope.invalid_state(
+            message=(
+                f"You have task {first.id} assigned but never claimed; "
+                "cannot idle until claimed or unclaimed."
+            ),
+            remediate=(
+                f"call {verb}(task_id='{first.id}') to start work, or"
+                " unclaim it first; then retry i_am_idle"
+            ),
+            context_briefing=briefing,
+        )
+
     async def _auto_pause_in_progress_tasks(self, agent_id: UUID) -> None:
         """Pause every in_progress task assigned to this agent.
 

tests/unit/gateway/test_choreographer_idle_guards.py

@@ -0,0 +1,161 @@
+"""Gate Set C: exit-time guards in Choreographer.i_am_idle.
+
+Pre-gateway behavior: an agent that signaled idle while owning unclaimed
+pending work was implicitly stuck because the orchestrator's PM-closure
+dispatcher would respawn them. The gateway makes this explicit:
+
+- pending-parent guard: refuse i_am_idle if caller has any pending task
+  assigned. They must call i_will_work_on / i_will_plan first.
+- in_progress preserved: existing auto-pause for in_progress remains.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+from unittest.mock import AsyncMock, MagicMock
+from uuid import uuid4
+
+import pytest
+from roboco.services.gateway.choreographer import Choreographer, ChoreographerDeps
+
+
+def _make_deps(**overrides: Any) -> ChoreographerDeps:
+    base: dict[str, Any] = {
+        "task": AsyncMock(),
+        "work_session": AsyncMock(),
+        "git": AsyncMock(),
+        "a2a": AsyncMock(),
+        "journal": AsyncMock(),
+        "audit": AsyncMock(),
+        "evidence_repo": AsyncMock(),
+    }
+    base.update(overrides)
+    repo = base["evidence_repo"]
+    for method in (
+        "list_unread_a2a",
+        "list_unread_mentions",
+        "list_pending_notifications",
+        "task_metadata_gaps",
+        "recent_team_activity",
+        "blockers_in_lane",
+        "journal_highlights_for_task",
+    ):
+        getattr(repo, method).return_value = []
+    return ChoreographerDeps(**base)
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_refuses_when_pending_assignment_exists() -> None:
+    """An agent with a pending (unclaimed) task assigned cannot exit."""
+    agent_id = uuid4()
+    pending_id = uuid4()
+    pending = MagicMock(id=pending_id, status="pending")
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = [pending]
+    task_svc.list_in_progress_for_agent.return_value = []
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    assert body["error"] == "invalid_state"
+    assert str(pending_id) in body["message"] or str(pending_id) in body["remediate"]
+    assert "i_will_work_on" in body["remediate"] or "i_will_plan" in body["remediate"]
+    task_svc.mark_agent_idle.assert_not_awaited()
+    task_svc.pause_for_agent.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_lets_pm_through_with_pending_remediate() -> None:
+    """The pending guard recommends i_will_plan when the agent is a PM."""
+    agent_id = uuid4()
+    pending_id = uuid4()
+    pending = MagicMock(id=pending_id, status="pending")
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = [pending]
+    task_svc.list_in_progress_for_agent.return_value = []
+    task_svc.agent_for.return_value = MagicMock(role="cell_pm", team="backend")
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    assert body["error"] == "invalid_state"
+    assert "i_will_plan" in body["remediate"]
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_lets_dev_through_with_pending_remediate() -> None:
+    """The pending guard recommends i_will_work_on for a developer."""
+    agent_id = uuid4()
+    pending_id = uuid4()
+    pending = MagicMock(id=pending_id, status="pending")
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = [pending]
+    task_svc.list_in_progress_for_agent.return_value = []
+    task_svc.agent_for.return_value = MagicMock(role="developer", team="backend")
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    assert body["error"] == "invalid_state"
+    assert "i_will_work_on" in body["remediate"]
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_ignores_non_pending_assigned_tasks() -> None:
+    """Other active states (claimed/in_progress/etc) don't trigger pending guard."""
+    agent_id = uuid4()
+    in_progress = MagicMock(id=uuid4(), status="in_progress")
+    task_svc = AsyncMock()
+    # Even though list_assigned_for_agent includes in_progress, only pending
+    # triggers the guard.
+    task_svc.list_assigned_for_agent.return_value = [in_progress]
+    task_svc.list_in_progress_for_agent.return_value = [in_progress]
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    assert body["error"] is None
+    # The auto-pause path should still fire for in_progress.
+    task_svc.pause_for_agent.assert_awaited_once_with(agent_id, in_progress.id)
+    task_svc.mark_agent_idle.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_with_no_assigned_tasks_proceeds_normally() -> None:
+    """Empty assignment list: no pending guard, no auto-pause, idle goes through."""
+    agent_id = uuid4()
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = []
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    assert body["error"] is None
+    assert body["status"] == "idle"
+    task_svc.pause_for_agent.assert_not_awaited()
+    task_svc.mark_agent_idle.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_pending_guard_runs_after_unread_check() -> None:
+    """Unread A2A check still wins; pending guard only runs after."""
+    agent_id = uuid4()
+    pending = MagicMock(id=uuid4(), status="pending")
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = [pending]
+    deps = _make_deps(task=task_svc)
+    deps.evidence_repo.list_unread_a2a.return_value = ["mention"]
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+    # Unread takes precedence and returns ok+idle_with_unread, NOT invalid_state
+    assert body["error"] is None
+    assert body["status"] == "idle_with_unread"
+    task_svc.mark_agent_idle.assert_not_awaited()