collections.abc isinstance checks return False

[pirapira]

Summary

collections.abc types (Iterable, Iterator, Mapping, Sequence, Set, etc.) are stubbed as .none values. While this allows imports to succeed, isinstance() checks against these types always return False.

Current behavior

from collections.abc import Iterable
isinstance([1, 2, 3], Iterable)  # Returns False (should be True)

Impact

• Low for current leanSpec E2E coverage — these types are mostly used in type annotations with from __future__ import annotations (deferred, never evaluated)
• Could affect runtime code that uses isinstance(x, Iterable) for duck-type dispatch
• state/state.py imports Iterable and Set but only uses them in annotations

Possible approach

Implement structural protocol checking: isinstance(x, Iterable) returns True if x has __iter__, etc. This matches CPython's collections.abc behavior via __subclasshook__.

Reference

• LeanPython/Interpreter/Eval.lean line 3128-3134 (collections.abc stub)