docs: record the wedged-app failure mode and point Phase 7 at it

AGENTS.md

@@ -148,7 +148,10 @@ Open maps and search a place.
 *DoD:* the Hub calls `/act` and the phone responds.
 
 **Phase 7 — Resilience**
-Wake the screen, reconnect after a drop, fail cleanly on a missing element.
+Wake the screen, reconnect after a drop, fail cleanly on a missing element, and
+handle an app that stops consuming input (a memory-starved phone can deliver a
+tap that the app never acts on — see `docs/phase-3-spotify-recipe.md`, attempts
+9, 10 and 13).
 *DoD:* a dropped ADB session recovers without a restart.
 
 **Phase 8 — Documentation**