GeezerVison

Summary

whats_left can currently compare a CPython introspection exception with a RustPython signature as if the exception were a reference signature. For example, the CI report records select.epoll.register with an AttributeError on the CPython side. That observation cannot establish a signature mismatch.

• Record whether inspect.signature raised, and list every CPython introspection failure explicitly as an uncomparable signature observation, including its exception. Aliases may appear more than once; the summary counts groups, not unique callables.
• Compare signatures only when the CPython reference succeeded. Do not label an inherited member missing solely because the CPython reference could not be inspected; genuine missing members and independent doc differences retain their prior handling.
• Do not list a module as fully implemented when its reference signatures contain unknowns.

This deliberately changes report accounting. Unknowns are visible, not treated as successful parity, and should be included in any future fail-closed CI coverage baseline. It overlaps the reporting work in #9565; a local source-reviewed composition retains both sets of changes.

Validation

• Independent source review checked all info-record constructors, inherited members, unknown aliases, result classification, and the local Preserve whats_left comparisons in CI #9565 composition.
• Focused synthetic execution of the extracted comparison confirmed that AttributeError/ValueError reference failures are reported as unknown, a true mismatch remains a mismatch, and an inherited unknown is not mislabeled missing.
• git diff --check, Ruff formatting/checks, and the normal commit hook passed. Full whats_left execution was not run locally: the coordinated RustPython native execution guard and lock are absent and the offline dependency cache is incomplete. Hosted three-platform CI is pending.

AI assistance

Implementation and source review were assisted by dot. The runtime does not expose its exact model version.