plan: small-fixes mop-up (0.8.5) — 5-task sequence

Each fix is TDD where applicable. T1 (chain.py) has two failing tests
pinning typing.get_type_hints resolution. T2 (pydantic.py) is a contract
narrowing verified by existing tests. T3 (LoggingMiddleware docs) is
docs-only. T4 (public-api test) is a test-quality change. T5 = release
notes + PR opening.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: lesnik512