docs(agents): record 2026-08-21 refactor cohort #883-#886 and PR #887 for #840

[pmrv]

Scheduled audit of AGENTS.md and its linked guides against the tracker state as of 2026-08-22. No code landed on main since the previous audit (#882), so the Quick Reference and Architecture claims are unchanged; the delta is issue-tracker state only.

• Add the 2026-08-21 refactor cohort under open proposals: Refactor: DestructuringMixin._raw_sub_digests hardcodes dispatch over built-in Digested subtypes — breaks gc()/count_reuses() for custom register_destructurer types #883 (_raw_sub_digests hardcodes built-in Digested subtypes, breaking gc()/count_reuses() for register_destructurer extensions — the one correctness gap of the batch), Refactor: sqlite/SQLAlchemy URL handling is hand-rolled twice and already diverged (config._rebase_url vs storage.sql._coerce_sqlite_url) #884 (sqlite URL handling hand-rolled twice and drifted on ~-expansion), Refactor: companion to #868 — wrapper.py hand-rolls XDG_CACHE_HOME the same way config.py hand-rolls XDG_CONFIG_HOME #885 (XDG_CACHE_HOME companion to Refactor: config discovery hand-rolls Linux-only XDG conventions despite "OS Independent" classifier #868), Refactor: benchmarks/benchmark_storage.py duplicates its 5-op timing harness between benchmark_storage_ops and benchmark_sql_ops (~90 lines) #886 (benchmark_storage.py five-op timing harness duplicated).
• Record PR fix(state): serialise BoundWrapper.func by value when not importable by reference #887 in flight against bug BoundWrapper only survives ProcessPoolExecutor under the fork start method #840 (BoundWrapper.__reduce__ pre-serialises func: pickle by reference, cloudpickle by value).
• Split the single Bugs/Feature-request paragraph into one-item-per-line sub-bullets so independent updates stop colliding in merges.

Verified still open and accurately described: PRs #797, #837, #873-#878, #879, #881.

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