[codex] Allow ternary __rpow__ in protocols

[EltonChang1]

Fixes #10786.

What changed

This skips the concrete reverse-operator signature validation for methods declared on protocol classes. Protocol declarations are structural requirements, so they should be able to describe a ternary __rpow__ method without mypy rejecting the declaration as an invalid binary reverse-operator signature.

A regression test covers a protocol that declares both ternary __pow__ and ternary __rpow__.

Validation

• pytest -n0 mypy/test/testcheck.py::TypeCheckSuite::check-protocols.test -k testProtocolTernaryRpow
• pytest -n0 mypy/test/testcheck.py::TypeCheckSuite::check-protocols.test
• pytest -n0 mypy/test/testcheck.py::TypeCheckSuite::check-classes.test -k 'ReverseOperator or Operator'
• Manual reproducer from the issue with python -m mypy --config-file=/dev/null now reports success.

Limitations

I did not run the full mypy test suite locally; the targeted protocol and adjacent operator tests passed.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[Copilot]

Pull request overview

This PR fixes mypy rejecting protocol declarations that include a ternary __rpow__ method by skipping the reverse-operator signature validation for methods defined on protocol classes. This aligns protocol method declarations with their role as structural requirements rather than concrete runtime operator implementations.

Changes:

• Skip check_reverse_op_method() for reverse-operator methods when the enclosing class is a protocol (TypeInfo.is_protocol).
• Add a regression test ensuring a protocol can declare ternary __pow__ and ternary __rpow__ without triggering an “Invalid signature” error.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
mypy/checker.py	Avoids reverse-operator signature validation for methods declared on protocol classes.
test-data/unit/check-protocols.test	Adds a regression test case for a protocol declaring ternary __pow__/__rpow__.

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