feat(gateway): C7 synthetic checkpoint on auto-pause

Smoke run 3 showed agents auto-pausing on i_am_idle (correct behavior
for non-terminal tasks) but capturing no checkpoint — panel's
Checkpoints column stayed empty. Pre-gateway parity: the auto-pause
path now writes a synthetic checkpoint summarizing state at pause-time
so the panel reflects reality.

Manual i_will_pause (G8a, deferred) will eventually let agents pass
their own checkpoint_summary; for now this synthetic write covers the
bare i_am_idle case which is what all current agents do.

Spec ref: docs/superpowers/specs/2026-05-12-post-smoke-3-fixes-design.md
section C7.

tests/unit/gateway/test_auto_pause_checkpoint.py

@@ -0,0 +1,215 @@
+"""Wave C7 (2026-05-12): auto-pause on i_am_idle writes a synthetic checkpoint.
+
+Smoke run 3 showed agents auto-pausing on i_am_idle (correct behavior for
+non-terminal tasks) but capturing no checkpoint — panel's Checkpoints column
+stayed empty. Pre-gateway parity: the auto-pause path now writes a synthetic
+checkpoint summarizing state at pause-time so the panel reflects reality.
+"""
+
+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_with_in_progress_task_writes_checkpoint() -> None:
+    """When i_am_idle auto-pauses an in_progress task, a synthetic checkpoint is
+    written with the correct task_id, agent_id, and a summary mentioning auto-pause.
+    """
+    agent_id = uuid4()
+    task_id = uuid4()
+
+    task_obj = MagicMock()
+    task_obj.id = task_id
+    task_obj.status = "in_progress"
+    task_obj.assigned_to = agent_id
+    task_obj.commits = []
+
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = [task_obj]
+    task_svc.pause_for_agent = AsyncMock()
+    task_svc.add_checkpoint = AsyncMock()
+
+    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.add_checkpoint.assert_awaited_once()
+    call_kwargs = task_svc.add_checkpoint.await_args
+    assert call_kwargs is not None
+    # task_id and agent_id must be present
+    assert call_kwargs.kwargs.get("task_id") == task_id or (
+        len(call_kwargs.args) >= 1 and call_kwargs.args[0] == task_id
+    )
+    second_arg_index = 1
+    assert call_kwargs.kwargs.get("agent_id") == agent_id or (
+        len(call_kwargs.args) > second_arg_index
+        and call_kwargs.args[second_arg_index] == agent_id
+    )
+    # Summary must mention auto-pause
+    state_summary = call_kwargs.kwargs.get("state_summary", "")
+    assert "auto-pause" in state_summary or "auto_pause" in state_summary
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_multiple_in_progress_tasks_each_get_checkpoint() -> None:
+    """Each auto-paused task gets its own synthetic checkpoint."""
+    agent_id = uuid4()
+    task_id_1 = uuid4()
+    task_id_2 = uuid4()
+
+    commit_a = MagicMock()
+    commit_a.sha = "aaa111"
+    commit_b = MagicMock()
+    commit_b.sha = "bbb222"
+
+    task_1 = MagicMock()
+    task_1.id = task_id_1
+    task_1.status = "in_progress"
+    task_1.commits = [commit_a, commit_b]
+
+    task_2 = MagicMock()
+    task_2.id = task_id_2
+    task_2.status = "in_progress"
+    task_2.commits = []
+
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = [task_1, task_2]
+    task_svc.pause_for_agent = AsyncMock()
+    task_svc.add_checkpoint = AsyncMock()
+
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    await c.i_am_idle(agent_id)
+
+    expected_checkpoint_count = 2
+    assert task_svc.add_checkpoint.await_count == expected_checkpoint_count
+    called_task_ids = {
+        kw.kwargs.get("task_id") or kw.args[0]
+        for kw in task_svc.add_checkpoint.await_args_list
+    }
+    assert task_id_1 in called_task_ids
+    assert task_id_2 in called_task_ids
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_with_commits_includes_last_three_in_remaining_work() -> None:
+    """Checkpoint's remaining_work contains refs for the last 3 commits."""
+    agent_id = uuid4()
+    task_id = uuid4()
+
+    commits = [MagicMock(sha=f"sha{i}") for i in range(5)]
+    task_obj = MagicMock()
+    task_obj.id = task_id
+    task_obj.status = "in_progress"
+    task_obj.commits = commits
+
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = [task_obj]
+    task_svc.pause_for_agent = AsyncMock()
+    task_svc.add_checkpoint = AsyncMock()
+
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    await c.i_am_idle(agent_id)
+
+    call_kwargs = task_svc.add_checkpoint.await_args
+    remaining = call_kwargs.kwargs.get("remaining_work", [])
+    # Last 3 commit SHAs should appear somewhere in remaining_work entries
+    last_3_shas = {c.sha for c in commits[-3:]}
+    mentioned_shas = {entry for entry in remaining if isinstance(entry, str)}
+    assert last_3_shas & mentioned_shas or any(
+        sha in str(remaining) for sha in last_3_shas
+    )
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_checkpoint_failure_does_not_block_auto_pause() -> None:
+    """If add_checkpoint raises, the auto-pause and idle response still succeed."""
+    agent_id = uuid4()
+    task_id = uuid4()
+
+    task_obj = MagicMock()
+    task_obj.id = task_id
+    task_obj.status = "in_progress"
+    task_obj.commits = []
+
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = [task_obj]
+    task_svc.pause_for_agent = AsyncMock()
+    task_svc.add_checkpoint = AsyncMock(side_effect=RuntimeError("DB timeout"))
+
+    deps = _make_deps(task=task_svc)
+    c = Choreographer(deps)
+
+    env = await c.i_am_idle(agent_id)
+    body = env.as_dict()
+
+    # The idle response must still succeed even though checkpoint write failed
+    assert body["error"] is None
+    assert body["status"] == "idle"
+    # The pause must still have happened
+    task_svc.pause_for_agent.assert_awaited_once_with(agent_id, task_id)
+    task_svc.mark_agent_idle.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_i_am_idle_with_no_active_task_skips_checkpoint() -> None:
+    """No active in_progress task → no auto-pause, no checkpoint written."""
+    agent_id = uuid4()
+
+    task_svc = AsyncMock()
+    task_svc.list_assigned_for_agent.return_value = []
+    task_svc.list_in_progress_for_agent.return_value = []
+    task_svc.add_checkpoint = AsyncMock()
+
+    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.add_checkpoint.assert_not_awaited()