feat: add /calendar/sync endpoint for multi-agent schedule sync

Returns today's slots for all agents on a claw instance, keyed by
agent_id. Used by HF Plugin to maintain a local schedule cache
instead of per-agent heartbeat.

Also records heartbeat for all agents on the instance.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/api/routers/calendar.py

@@ -361,6 +361,62 @@ def agent_heartbeat(
     )
 
 
+@router.get(
+    "/sync",
+    summary="Sync today's schedules for all agents on a claw instance",
+)
+def sync_schedules(
+    x_claw_identifier: str = Header(..., alias="X-Claw-Identifier"),
+    db: Session = Depends(get_db),
+):
+    """Return today's slots for all agents belonging to the given claw instance.
+
+    Used by the HF OpenClaw plugin to maintain a local schedule cache.
+    Returns a dict of { agent_id: [slots] } for all agents with matching
+    claw_identifier.
+    """
+    today = date_type.today()
+
+    # Find all agents on this claw instance
+    agents = (
+        db.query(Agent)
+        .filter(Agent.claw_identifier == x_claw_identifier)
+        .all()
+    )
+
+    schedules: dict[str, list[dict]] = {}
+    for agent in agents:
+        # Get real slots for today
+        real_slots = (
+            db.query(TimeSlot)
+            .filter(
+                TimeSlot.user_id == agent.user_id,
+                TimeSlot.date == today,
+                TimeSlot.status.notin_(list(_INACTIVE_STATUSES)),
+            )
+            .all()
+        )
+        items = [_real_slot_to_item(s).model_dump(mode="json") for s in real_slots]
+
+        # Get virtual plan slots
+        virtual_slots = get_virtual_slots_for_date(db, agent.user_id, today)
+        for vs in virtual_slots:
+            items.append(_virtual_slot_to_item(vs).model_dump(mode="json"))
+
+        schedules[agent.agent_id] = items
+
+    # Record heartbeat for liveness
+    for agent in agents:
+        record_heartbeat(db, agent)
+    db.commit()
+
+    return {
+        "schedules": schedules,
+        "date": today.isoformat(),
+        "agent_count": len(agents),
+    }
+
+
 @router.patch(
     "/slots/{slot_id}/agent-update",
     response_model=TimeSlotEditResponse,