Use accessibility overlays for gesture zones

[Dragonk]

Summary

Gesture windows have been migrated from TYPE_APPLICATION_OVERLAY to TYPE_ACCESSIBILITY_OVERLAY and are now owned by EdgeGestureAccessibilityService instead of a standalone foreground overlay service.

The window logic that lived in EdgeOverlayService (a foreground LifecycleService) was extracted into a reusable EdgeOverlayController that is created in EdgeGestureAccessibilityService.onServiceConnected() and torn down in onUnbind()/onDestroy(). Every gesture-related window — the touch zones, the back arrow, and the home handle — now uses WindowManager.LayoutParams.TYPE_ACCESSIBILITY_OVERLAY.

Why

Ogesture already depends on an AccessibilityService for the Back/Home/Recents navigation actions. Two problems came from drawing the gesture zones as ordinary application overlays:

1. Protected screens hide them. Android Settings (and other secure system screens) set HIDE_NON_SYSTEM_OVERLAY_WINDOWS, which removes non-system application overlays — so Ogesture's gesture zones disappeared there and the user had to fall back to the phone's own navigation.
2. A persistent system notification. Application overlays drawn with SYSTEM_ALERT_WINDOW cause Android's WindowManager to generate the ongoing "displaying over other apps" AlertWindowNotification for the app.

Because the gesture zones are an accessibility-driven feature owned by an already-enabled AccessibilityService, they fit TYPE_ACCESSIBILITY_OVERLAY: trusted windows that are not hidden on secure screens and do not require SYSTEM_ALERT_WINDOW. This uses the proper accessibility-overlay model for an accessibility-driven gesture feature — it does not bypass Android security; the accessibility service still requires explicit user consent.

What changed

• New EdgeOverlayController owns the gesture-zone and indicator windows, created and destroyed by EdgeGestureAccessibilityService. It is decoupled from the concrete service through a small GestureDispatcher interface (trigger + replay).
• TYPE_ACCESSIBILITY_OVERLAY for the touch-zone windows and for BackIndicator / HomeIndicator (new windowType constructor param defaulting to the accessibility overlay).
• Removed SYSTEM_ALERT_WINDOW from the manifest, and all Settings.canDrawOverlays(...) checks, the ACTION_MANAGE_OVERLAY_PERMISSION setup flow, the "Display over other apps" setup requirement, and the gestures-off overlay failure path.
• Removed the obsolete foreground overlay service EdgeOverlayService and its notification channel/running notification.
• Removed BootReceiver — it only revived EdgeOverlayService. Android rebinds the AccessibilityService after process death/reboot on its own, and the controller re-attaches zones if the master switch is still on, so the boot receiver is no longer needed.
• Removed obsolete permissions FOREGROUND_SERVICE, FOREGROUND_SERVICE_SPECIAL_USE, POST_NOTIFICATIONS, and RECEIVE_BOOT_COMPLETED, plus the specialUse service metadata and the androidx.lifecycle.service dependency.
• Setup UI simplified — the setup card lists Accessibility + unrestricted battery only; enabling gestures depends only on the service being bound and unrestricted battery. The in-app "gestures won't work on Settings" notice and the related remember bullet were removed/rewritten.
• Documentation updated — README "How it works" and the PRIVACY permission table reflect the accessibility-overlay architecture and no longer mention Display-over-apps, the foreground service, or the Settings limitation.
• Tests updated — added pure-data regression tests for the gesture-zone set, swipe-direction mapping, and Back/Home/Recents action wiring; the instrumented test accepts the debug applicationId suffix.

Accessibility privacy is unchanged: canRetrieveWindowContent stays false, and only the foreground package name is read (for per-app pass-through) — no window-content scraping, no broadened event collection.

Behavior preserved

• Left-edge and right-edge Back
• Bottom Home
• Bottom swipe-and-hold Recents
• Gesture visual indicators (back arrow peek, home handle lift)
• Haptic feedback
• Per-app excluded / pass-through behavior
• Unused-touch replay via dispatchGesture
• The replay/interactivity workarounds (held-zone untouchable+alpha 0, indicator-hide-before-inject grace) — preserved verbatim; the behaviour change is limited to the window type and ownership
• Taps and long presses near gesture zones
• Keyboard foreground-tracking behavior
• Rotation / display-geometry changes (re-lays out zones)
• Service reconnect does not create duplicate windows (rebuild() detaches all first)

Validation

./gradlew testDebugUnitTest   -> BUILD SUCCESSFUL (unit tests pass, incl. new GestureZoneLayoutTest)
./gradlew lintDebug           -> BUILD SUCCESSFUL (0 errors, 0 fatals; 19 warnings, all pre-existing on main)
./gradlew assembleDebug       -> BUILD SUCCESSFUL
./gradlew assembleRelease     -> BUILD SUCCESSFUL

Static verification: production code has no functional dependency on TYPE_APPLICATION_OVERLAY, SYSTEM_ALERT_WINDOW, Settings.canDrawOverlays, or ACTION_MANAGE_OVERLAY_PERMISSION (the only remaining mentions are explanatory KDoc comments in EdgeOverlayController). The merged release manifest requests no SYSTEM_ALERT_WINDOW, FOREGROUND_SERVICE/FOREGROUND_SERVICE_SPECIAL_USE, POST_NOTIFICATIONS, or RECEIVE_BOOT_COMPLETED; the only service declared is the accessibility service and there is no receiver. Instrumentation tests were not run (no device available to the build environment).

Real-device validation

Tested on a real Xiaomi/HyperOS Android device using a locally built release APK (signed with the standard Android debug keystore; no signing key was created or committed). Confirmed:

• edge gestures remain functional inside Android Settings and protected Settings screens that previously hid the application overlays;
• gesture overlays are no longer suppressed as ordinary application overlays on those screens;
• the persistent Android "displaying over other apps" system notification for Ogesture is gone.

This directly validates the two main user-facing goals of the migration.