[sang765]

Summary

RenderEffect/Haze cannot blur live content below Android 12 (API 31), so on those devices the new floating navigation bar and the top-app-bar overflow menu degraded to a flat tint.

This makes them show a real backdrop blur there by capturing the hazeSource content into a GraphicsLayer, reading it back, downscaling it and blurring it with the existing pure-Kotlin ImageBlurUtils stack blur, then rendering it behind the bar/menu.

The capture modifier is a no-op on API >= 31, so the modern Haze/RenderEffect path is untouched and pays zero cost.

Changes

• ui/component/BackdropSnapshot.kt (new) — BackdropSnapshot holder + Modifier.backdropSnapshotSource(), which records the node, reads it back on a throttled loop (periodic for the navbar, gated on expanded for the menu), downscales to <= 480px and stack-blurs into the holder.
• ui/component/FloatingBarBlurBackground.kt — API < 31 branch renders the blurred snapshot (ContentScale.Crop, BottomCenter) + tint. Adds optional backdrop param (default null, so the MiniPlayer path is unchanged).
• ui/component/FloatingNavigationToolbar.kt — passes backdrop through to FloatingBarBlurBackground.
• ui/component/TopAppBarOverflowMenu.kt — API < 31 branch renders the blurred snapshot (ContentScale.Crop, TopEnd) + tint; extracts the shared menu items into OverflowMenuItems.
• MainActivity.kt — creates the two holders, attaches the capture to the two hazeSource nodes, gates the menu holder on expanded, and passes backdrop to the two consumers.

Notes / limitations

• The backdrop is a snapshot approximation (bottom-center strip behind the navbar, top-right region behind the menu), not pixel-perfect live blur like Haze — acceptable once blurred, but worth eyeballing on a real API 30/31 device.
• Blur radii (navbar 10px, menu 18px on the <= 480px snapshot) and tint alphas mirror the current Haze style values; easy to tune.
• Not build-verified on an API < 31 device in this environment.

[sang765]

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