`StdioTransport` subclasses validate the command before calling
`super().__init__()`, so an object whose construction raised never got a
`_stop_event`. Garbage collection then ran `__del__`, which dereferenced it, and
CPython printed an unraisable `AttributeError` on stderr — burying the error the
caller was meant to see (`PythonStdioTransport`, `NodeStdioTransport` and
`UvStdioTransport` can each reach that path).
`__del__` now reads the event with `getattr` and skips it when the instance never
finished initialising.
Fixes#5255🤖 Generated with Claude Code
Co-authored-by: nate nowack <thrast36@gmail.com>
56652209ec