Complete Android animation runtime integration and validation

[ProGraMajster]

Summary

Completes Android runtime integration for the shared ModernFormsNext animation system without introducing Android-only schedulers, easing, or interpolation.

This integrates the shared AnimationScheduler with Choreographer-based frame pacing and covers lifecycle pause/resume/rebase, Android animator-duration scaling, stable multi-touch ownership, interaction effects, theme transitions, layout and visual-state transitions, cleanup, diagnostics, and the Android diagnostic sample.

Architecture

The platform-neutral runtime remains responsible for:

• animation models and easing
• interpolation
• AnimationScheduler
• ThemeManager
• InteractionEffect, RippleEffect, and PressScaleEffect
• LayoutTransition and VisualStateTransition
• logical and presentation state

The Android backend is limited to:

• the Choreographer frame source
• the lifecycle bridge
• MotionEvent translation
• density conversion
• animator-duration-scale observation
• native callback and subscription cleanup
• Android runtime diagnostics

No second Android-only animation system was created.

Frame pacing

• Uses one process-wide Choreographer source for the shared scheduler.
• Keeps at most one native frame callback pending.
• Requests callbacks only while shared animation demand and an attached/resumed surface are both present.
• Returns to idle after the final animation and wakes for later work.
• Uses the scheduler's monotonic clock and does not assume 60 Hz.
• Dropped and long frames advance to the current presentation value without accumulating a frame backlog.
• Late-binds the platform frame source, so early AnimationScheduler.Default access cannot permanently select the fallback ticker.
• Active fallback demand hands off once to Choreographer without delivering a duplicate scheduler tick.

Lifecycle

• Backgrounding stops frame demand and pauses the shared scheduler.
• Resume rebases scheduler time so background elapsed time is excluded and cannot produce catch-up animation.
• Attach/resume activates the Android surface; pause/stop/detach/dispose deactivates it.
• A monotonic lifecycle version prevents stale foreground work from overtaking a newer background event.
• Choreographer is acquired and reconciled on Android's main Looper.

Reduced motion

Android ANIMATOR_DURATION_SCALE is read through a lifecycle-aware ContentObserver using the application context and a main-thread Handler.

• scale == 0: active animations publish their exact target immediately and the scheduler remains idle.
• scale < 1: newly started animations use shortened durations.
• scale == 1: normal duration.
• scale > 1: newly started animations use extended durations.
• Invalid or unavailable reads use a diagnostic fallback of 1.0.
• Observation is enabled only while needed in the foreground and is unregistered during background/shutdown/disposal cleanup.

Multi-touch

• Uses stable Android pointer IDs for shared pointer capture and effect ownership.
• Uses ActionIndex only to find the changed pointer for DOWN/POINTER_DOWN and POINTER_UP/UP.
• MOVE translates every currently present pointer.
• CANCEL clears every tracked pointer.
• Pointer-index reordering does not transfer ownership.
• Ripple instances retain independent pointer ownership.
• Press-scale ownership and cancellation remain in the shared effect implementation.

Cleanup and leak prevention

Cleanup covers scheduler entries, native frame callbacks, pointer captures, lifecycle and invalidation subscriptions, ContentObserver registration, detach/reparent/dispose, and surface recreation.

The Android activity tracker uses a WeakReference for the current Activity. The frame source does not retain a View or Activity, and reduced-motion observation uses application context. Automated weak-reference and lifecycle tests cover managed cleanup paths; no device-profiler leak claim is made.

Automated validation

• Full restore: PASS
• Debug solution build: PASS, 0 warnings / 0 errors
• Release solution build: PASS, 0 warnings / 0 errors
• All tests: 1083/1083
  • Core: 820/820
  • Android backend: 72/72
  • Designer: 168/168
  • Windows backend: 7/7
  • Cross-platform sample: 16/16
• Android SmokeTest Debug/Release: PASS
• CrossPlatform.Sample Android Debug/Release: PASS
• VSIX Debug/Release validation: PASS
• git diff --check: PASS

The complete test count was confirmed from a clean worktree at the exact feature SHA because nested worktrees under artifacts can otherwise contaminate ReleaseVersionConsistencyTests.

Manual emulator validation

A manual emulator smoke test confirmed only:

• Android host startup
• basic AnimationScheduler/Choreographer operation
• animation start and retargeting
• theme transition
• TextBox
• Android soft keyboard / IME
• no visible crash in that scenario

Remaining device-specific validation

The following still require deeper manual/device validation and are not claimed as completed here:

• real two-finger multi-touch
• system-generated ACTION_CANCEL
• dynamic animator-scale changes while the app is running
• long background intervals, screen off/on, and app switching
• rapid repeated rotation and resize
• Activity/surface recreation during active effects
• 90/120 Hz displays
• visual behavior under dropped or unusually long frames
• device-profiler leak checks
• physical-device validation
• more complex IME/composition scenarios

Closes #29