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fix(server): deregister terminated streamable HTTP sessions #3302

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fix(server): deregister terminated streamable HTTP sessions #3302

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3 changes: 3 additions & 0 deletions src/mcp/server/streamable_http_manager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -281,6 +281,9 @@ async def _handle_stateful_request(self, scope: Scope, receive: Receive, send: S
if transport.idle_scope is not None and self.session_idle_timeout is not None:
transport.idle_scope.deadline = anyio.current_time() + self.session_idle_timeout # pragma: no cover
await transport.handle_request(scope, receive, send)
if transport.is_terminated:
self._server_instances.pop(request_mcp_session_id, None)
self._session_owners.pop(request_mcp_session_id, None)
return

if request_mcp_session_id is None:
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30 changes: 30 additions & 0 deletions tests/server/test_streamable_http_manager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -304,6 +304,36 @@ async def mock_receive():
assert not manager._server_instances, "No sessions should be tracked after the only session exits gracefully"


@pytest.mark.anyio
async def test_terminated_existing_session_is_removed_from_registry(
running_manager: tuple[StreamableHTTPSessionManager, Server],
):
manager, _app = running_manager
session_id = "terminated-session"
transport = AsyncMock()
transport.is_terminated = True
transport.idle_scope = None
manager._server_instances[session_id] = transport

@cubic-dev-ai cubic-dev-ai Bot Aug 13, 2026

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P3: This regression test does not verify _session_owners cleanup because it never adds session_id to _session_owners before the request. Seed that registry first so the assertion can fail if owner removal breaks.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At tests/server/test_streamable_http_manager.py, line 316:

<comment>This regression test does not verify `_session_owners` cleanup because it never adds `session_id` to `_session_owners` before the request. Seed that registry first so the assertion can fail if owner removal breaks.</comment>

<file context>
@@ -304,6 +304,36 @@ async def mock_receive():
+    transport = AsyncMock()
+    transport.is_terminated = True
+    transport.idle_scope = None
+    manager._server_instances[session_id] = transport
+
+    scope = {
</file context>


scope = {
"type": "http",
"method": "DELETE",
"path": "/mcp",
"headers": [(MCP_SESSION_ID_HEADER.encode(), session_id.encode())],
}

async def mock_receive():
return {"type": "http.request", "body": b"", "more_body": False}

async def mock_send(_message: Message):
pass

await manager.handle_request(scope, mock_receive, mock_send)

assert session_id not in manager._server_instances
assert session_id not in manager._session_owners


@pytest.mark.anyio
async def test_stateful_session_cleanup_on_exception(running_manager: tuple[StreamableHTTPSessionManager, Server]):
manager, _app = running_manager
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