FP Review Checklist (Module 09)

• Purity: no hidden I/O, globals, randomness, timestamps in core paths.
• Immutability: public dataclasses are frozen; no mutable defaults; no leaked internal mutation.
• Stdlib-first: prefer itertools / functools / operator before adding new helpers.
• Errors: use Result/ErrInfo and explicit policies; avoid broad except Exception in core.
• Streaming: avoid unbounded buffering; if concurrency is used, ensure bounded policies.
• Ports/adapters: ports return effect descriptions; interpreters live in shells/adapters only.
• Tests: add properties for laws/guarantees when introducing new operators/policies.