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fix: propagate SSE stream errors to waiting requests #2122

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heyhayes wants to merge 5 commits into from
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fix: propagate SSE stream errors to waiting requests #2122

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ddd2a37
fix: change _handle_reconnection to return bool and fix infinite recu…
heyhayes Feb 21, 2026
75cd668
fix: propagate error when SSE stream ends without a response
heyhayes Feb 21, 2026
0efb392
fix: stop infinite GET stream reconnection on repeated empty connections
heyhayes Feb 21, 2026
ae0bc81
Log warning for unhandled exceptions in default message handler
heyhayes Feb 21, 2026
f0af07e
test: cover branch where reconnection exhausts max attempts
heyhayes Feb 21, 2026
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Log warning for unhandled exceptions in default message handler 
Transport errors that are not tied to a specific pending request (e.g.,
GET stream failures) were silently swallowed by the default message
handler. Add a warning log so these exceptions are at least visible in
logs as an observability safety net.

Github-Issue: #1401
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@heyhayes
heyhayes committed Feb 21, 2026
commit ae0bc81a22ba997a2de1eac6c6fd83b58594f37d
2 changes: 2 additions & 0 deletions src/mcp/client/session.py
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,8 @@ async def __call__(
async def _default_message_handler(
message: RequestResponder[types.ServerRequest, types.ClientResult] | types.ServerNotification | Exception,
) -> None:
if isinstance(message, Exception):
logger.warning("Unhandled exception in message handler: %s", message)
await anyio.lowlevel.checkpoint()


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