Ψ-W1-T3 review remediation: soften the double-fire claim to unspecified-by-SDK, mark the unload mirror [verify — DAW], fix stale comment, drop redundant assertions, dedupe hook-partitioning comments, drop what-comment; file the action_registry test-seam deferral.

docs/PLAN.md

@@ -2412,7 +2412,10 @@ must not touch `main.cpp`; this track is why.
   (`custom_action` / `hookcommand2` / `-custom_action` mirror) — a deliverable of this
   track.
 - **DAW-verification obligation:** Daniel adds the action to the Media Explorer toolbar
-  and imports from it; also confirms the Main-section binding still fires.
+  and imports from it; also confirms the Main-section binding still fires. Also: unload,
+  reload, confirm no duplicate Media Explorer entry — the `-custom_action` unload mirror
+  is unconfirmed against the SDK header (root `CLAUDE.md` §"REAPER extension contract",
+  `[verify — DAW]`), and if unsupported the entry leaks across a reload.
 
 **Open questions.** `[verify]` re-verify `custom_action_register_t` and `hookcommand2`
 argument order/types against the SDK headers at implementation time (root `CLAUDE.md`