fix(android): anchor session replay masks to the rendered frame and cover stretch overscroll (Rubber animation)

[abelonogov-ld]

Summary

Session replay masks slipped off content while the screen was moving. Two independent causes, one per commit.

Frame alignment. Mask geometry was read in a Choreographer frame callback, which runs in the animation phase before that frame's measure/layout/draw, so it described the previous traversal; PixelCopy then returned whatever buffer the surface held, usually older still. Nothing guaranteed the captured pixels fell between the before and after mask passes, so the convex hull spanning them could be covering the wrong interval.

FrameSynchronizer now reads geometry from inside the draw pass that produces a frame (ViewTreeObserver.OnDrawListener) and waits for that frame to finish rendering (Window.addOnFrameMetricsAvailableListener, API 24+) before the caller copies pixels. The listener is registered before the draw so the frame being waited for is the frame that was sampled. Pixels are now never older than the before pass nor newer than the after pass, which is the bracket the hull assumes.

Stretch overscroll. Android 12+ rubber-band overscroll is a RenderEffect recorded into the scrollable's display list and applied by the RenderThread. No view moves, no layout changes, and Compose's boundsInWindow is equally unaware, so this one is not a timing problem at all — the geometry faithfully describes an undistorted layout that was never rendered, and frame alignment can't help.

StretchOverscroll asks the container's EdgeEffects how hard they are being pulled and converts that to pixels with the same curve the framework uses (EdgeEffect.dampStretchVector, scaled by the container size, capped at 3.2% of it) plus 25% slack. MaskCollector grows everything the stretched container's subtree emitted — rect and transformed quad alike — outward from each mask's own center. Growth is symmetric per axis because nothing in the tree reveals which way content slid. Compose keeps its effects in the modifier chain rather than on a view, so ComposeStretchOverscroll follows LayoutInfo.getModifierInfo() by class name to the same EdgeEffectWrapper; the shapes were checked against foundation 1.7.0 and 1.11.2, covering both the draw-modifier and node forms.

Inflation logs at debug (Stretch overscroll: grew N mask(s) by (dx, dy)px) so a slip can be attributed to detection or to amount.

Known limits

• Framework scrollables (ScrollView, ListView) keep their edge effects in non-SDK fields that reflection is blocked from on modern Android, so they get no inflation. RecyclerView, ViewPager2, NestedScrollView, Compose and app-defined containers are all covered.
• Masks cover slightly more than the content during an overscroll, deliberately.
• Frame alignment degrades gracefully: an idle tree that never draws falls back to reading it directly and skips the frame wait, and below API 24 only the wait is skipped.

Test plan

• :lib:testDebugUnitTest green, including 25 new tests: draw anchoring, the register-before-draw ordering, both fallbacks, sampling failures kept out of the draw pass, displacement against the framework's curve, per-axis attribution, inflation geometry, and that only the stretched subtree grows.
• :lib:lintDebug reports no new findings (five pre-existing NewApi errors elsewhere remain).
• Verified on device: masks stay on content through rubber-band scrolling.

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Note

Overview
Fixes session replay masks slipping off content during scroll and animation by aligning mask sampling with rendered frames and inflating masks for stretch overscroll.

Frame alignment: ImageCaptureService replaces raw Choreographer callbacks with FrameSynchronizer, which samples mask geometry inside OnDrawListener (not pre-draw animation phase) and waits for frame completion via OnFrameMetricsAvailableListener before pixel copy. Before/after mask passes now bracket the captured frame for MaskApplier.mergeMasksMap's convex hull.

Stretch overscroll: On API 31+, StretchOverscroll and ComposeStretchOverscroll read EdgeEffect pull distance (reflection / Compose modifier chain) and map it through the framework stretch curve with slack. Mask.inflate and MaskCollector grow only masks from the stretched subtree (identity snapshots survive culling). This covers RenderThread distortion the view tree cannot describe.

Adds unit tests for synchronizer ordering, inflation geometry, and displacement math.

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