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Evan Mattson 2a9b68d1bd Python: Fix MCPStreamableHTTPTool leaking asyncio.CancelledError when MCP server is unreachable (#5687 )

* fix: wrap asyncio.CancelledError in ToolException in _connect_on_owner (#5667)

asyncio.CancelledError is a BaseException (not Exception) in Python 3.8+.
When an MCP server is unreachable, the MCP library's internal anyio task
group raises CancelledError, which escaped all three 'except Exception'
handlers in _connect_on_owner(). This propagated through
_run_lifecycle_owner -> _run_on_lifecycle_owner -> connect -> __aenter__,
bypassing user except Exception blocks entirely.

Fix: change the three except-Exception clauses in _connect_on_owner to
'except (Exception, asyncio.CancelledError)' so spurious CancelledErrors
from the MCP transport layer are caught and wrapped in ToolException,
consistent with the method's documented contract.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(mcp): propagate genuine task CancelledError in connect() (#5667)

On Python >= 3.11, check task.cancelling() > 0 before wrapping
CancelledError as ToolException in the three except blocks inside
_connect_on_owner(). When the current task is being cancelled by its
caller, the CancelledError now propagates after cleanup, consistent
with the existing pattern at _mcp.py:560-564 and _runner.py:115-120.

On Python < 3.11 task.cancelling() is unavailable, so MCP-internal
CancelledErrors still cannot be reliably distinguished from
caller-driven cancellation; they continue to be wrapped as
ToolException with a comment documenting the trade-off.

Tests:
- Add cleanup assertion to transport-creation CancelledError test
- Add MCPStdioTool variants exercising the 'command' message branches
  for both transport-creation and initialize CancelledError paths
- Add Python 3.11+-gated tests verifying genuine task cancellation
  propagates (and still cleans up) for transport and initialize stages

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(mcp): log CancelledError with exc_info before wrapping in ToolException (#5667)

CancelledError inherits from BaseException (not Exception) on Python >= 3.8,
so the 'inner_exception=ex if isinstance(ex, Exception) else None' guard
always yields None for CancelledError. This means ToolException.__init__
calls logger.log(level, message, exc_info=None), dropping the traceback.

Add an explicit logger.debug(error_msg, exc_info=ex) before each
raise ToolException(...) in the three CancelledError handlers so the
full traceback is preserved in debug logs when MCP-internal cancellation
is wrapped rather than propagated.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review feedback for #5667: Python: [Bug]: Error Handling Issue regarding Python MCPStreamableHTTPTool Class

* refactor(_mcp): extract cancellation helper, fix session error msg and exc_info

- Extract _should_propagate_cancelled_error() helper to eliminate duplicated
  genuine-cancellation detection logic across the three connect() except blocks
- Fix session-creation ToolException message to include exception details
  (e.g. 'Failed to create MCP session: <ex>') matching the transport and
  initialize failure paths
- Change exc_info=ex to exc_info=True in all three logger.debug() calls
  for idiomatic logging
- Add tests for _should_propagate_cancelled_error helper
- Add regression test asserting session error message includes exception text
- Add test verifying logger.debug is called with exc_info=True

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refactor: factor out _close_and_check_cancelled helper in _connect_on_owner

Addresses review comment on PR #5687:

1. Add _close_and_check_cancelled() helper method that combines
   _safe_close_exit_stack() + _should_propagate_cancelled_error() into a
   single await-able call. This eliminates the duplicated close-then-check
   pattern that appeared identically in all three connect phases (transport,
   session, initialize), reducing future drift risk.

2. Comments 2 and 3 (missing {ex} in session error message and non-idiomatic
   exc_info=ex) were already addressed in the current code: all error messages
   include {ex} and all logger.debug calls use exc_info=True.

3. Add test_connect_genuine_cancellation_during_session_creation_propagates
   to cover the previously untested genuine-cancellation path in the
   session-creation phase (transport and initialize phases already had tests).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review feedback for #5667: review comment fixes

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>