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fix(core): isolate shared initialization cancellation #745

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2 changes: 1 addition & 1 deletion packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,7 @@ async def _ensure_initialized(
self._init_task = asyncio.create_task(
self._initialize_session(headers=headers)
)
await self._init_task
await asyncio.shield(self._init_task)

@property
def base_url(self) -> str:
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34 changes: 34 additions & 0 deletions packages/toolbox-core/tests/mcp_transport/test_base.py
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Expand Up @@ -152,6 +152,40 @@ async def slow_init(*args, **kwargs):

transport._initialize_session.assert_called_once()

@pytest.mark.asyncio
async def test_cancelled_waiter_does_not_cancel_shared_initialization(self, mocker):
"""Cancelling one waiter leaves the shared initialization running."""
session = AsyncMock(spec=ClientSession)
transport = ConcreteTransport("http://fake-server.com", session=session)
init_started = asyncio.Event()
allow_init = asyncio.Event()

async def slow_init(*args, **kwargs):
init_started.set()
await allow_init.wait()

mocker.patch.object(
transport,
"_initialize_session",
new_callable=AsyncMock,
side_effect=slow_init,
)

cancelled_waiter = asyncio.create_task(transport._ensure_initialized())
await init_started.wait()
surviving_waiter = asyncio.create_task(transport._ensure_initialized())
await asyncio.sleep(0)

cancelled_waiter.cancel()
with pytest.raises(asyncio.CancelledError):
await cancelled_waiter

allow_init.set()
assert await asyncio.gather(surviving_waiter, return_exceptions=True) == [None]

await transport._ensure_initialized()
transport._initialize_session.assert_awaited_once()

def test_convert_tool_schema_valid(self, transport):
"""Test converting a valid MCP tool schema."""
raw_tool = {
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