TODO_DEFERRED: add typing convention audit

Audit typing for collections.abc parameter types and concrete
lowercase return types (PEP 585).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Technologicat

TODO_DEFERRED.md

@@ -1,6 +1,8 @@
 # Deferred Issues
 
-Next unused item code: D8
+Next unused item code: D9
 
 - **D5**: `dispatch.py` — moved to GitHub issue #99. Dispatch-layer improvements for parametric ABCs (warn/error on indistinguishable multimethods). Typecheck-layer part resolved.
 
+
+- **D8: Audit typing: abstract parameter types, concrete return types**: Parameters should use abstract types from `collections.abc` (`Mapping`, `Sequence`, `Iterable`) for widest-possible-accepted semantics. Return types should use concrete lowercase builtins (`tuple[int, int]`, `list[int]`, `dict[str, int]`) — PEP 585, Python 3.9+. The capitalized `typing` forms (`Dict`, `List`, `Tuple`) are deprecated aliases for the builtins and offer no extra width — avoid them. Audit existing type hints across the codebase for consistency. (Discovered during raven-cherrypick compare mode planning, 2026-03-30.)