fix(webui): clear stuck streaming after reconnect and improve stop reliability

After a gateway restart or websocket reconnect, the UI stays stuck in
processing state because reconnecting clients only replay running status
when a turn is active, never push idle when no turn is running.

Fix _hydrate_after_subscribe to always push goal_status (running with
started_at when turn is active, idle when no turn is running) so the
frontend can reset its processing indicator on reconnect.

Also fix cmd_stop reporting 'No active task to stop' when a task is
actually processing by draining the pending injection queue in addition
to cancelling active tasks. This prevents mid-turn injection deadlocks
and gives accurate task counts.

tests/command/test_stop_pending_queue.py

@@ -0,0 +1,81 @@
+"""Test cmd_stop drains pending queue to prevent mid-turn injection deadlock."""
+
+import asyncio
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from nanobot.bus.events import OutboundMessage
+from nanobot.command.builtin import cmd_stop
+from nanobot.command.router import CommandContext
+
+
+@pytest.mark.asyncio
+async def test_cmd_stop_drains_pending_queue():
+    """cmd_stop should drain pending queue in addition to cancelling active tasks."""
+    mock_loop = MagicMock()
+    mock_loop._cancel_active_tasks = AsyncMock(return_value=1)
+    mock_loop._pending_queues = {}
+    
+    pending = asyncio.Queue()
+    await pending.put("msg1")
+    await pending.put("msg2")
+    mock_loop._pending_queues["test-session"] = pending
+    
+    ctx = CommandContext(
+        msg=MagicMock(channel="websocket", chat_id="test-chat", metadata={}),
+        session=None,
+        key="test-session",
+        raw="/stop",
+        loop=mock_loop,
+    )
+    
+    result = await cmd_stop(ctx)
+    
+    assert isinstance(result, OutboundMessage)
+    assert "Stopped 3 task(s)" in result.content  # 1 cancelled + 2 drained
+    assert "test-session" not in mock_loop._pending_queues
+
+
+@pytest.mark.asyncio
+async def test_cmd_stop_with_empty_pending_queue():
+    """cmd_stop should work correctly when pending queue is empty."""
+    mock_loop = MagicMock()
+    mock_loop._cancel_active_tasks = AsyncMock(return_value=2)
+    mock_loop._pending_queues = {}
+    
+    pending = asyncio.Queue()
+    mock_loop._pending_queues["test-session"] = pending
+    
+    ctx = CommandContext(
+        msg=MagicMock(channel="websocket", chat_id="test-chat", metadata={}),
+        session=None,
+        key="test-session",
+        raw="/stop",
+        loop=mock_loop,
+    )
+    
+    result = await cmd_stop(ctx)
+    
+    assert "Stopped 2 task(s)" in result.content
+    assert "test-session" not in mock_loop._pending_queues
+
+
+@pytest.mark.asyncio
+async def test_cmd_stop_no_pending_queue():
+    """cmd_stop should work when no pending queue exists."""
+    mock_loop = MagicMock()
+    mock_loop._cancel_active_tasks = AsyncMock(return_value=0)
+    mock_loop._pending_queues = {}
+    
+    ctx = CommandContext(
+        msg=MagicMock(channel="websocket", chat_id="test-chat", metadata={}),
+        session=None,
+        key="test-session",
+        raw="/stop",
+        loop=mock_loop,
+    )
+    
+    result = await cmd_stop(ctx)
+    
+    assert "No active task to stop" in result.content