iOS Simulator: SIGSEGV in -[RiveFactory decodeImage:] when a RiveView with referenced image assets mounts again after the last RiveView unmounted #449

Versions: rive-react-native 9.8.6 (RiveRuntime 6.24.0), React Native 0.87, iOS Simulator on an Apple-silicon Mac. Not reproduced on a physical iPhone.

What happens: the app crashes natively (SIGSEGV) in -[RiveFactory decodeImage:], called from RiveReactNativeView.processAssetBytes, when a RiveView that supplies images through referencedAssets mounts again after every RiveView had been unmounted. The first mount always works.

Steps

1. Render a RiveView for a .riv with two referenced image assets, supplied as URLs via referencedAssets.
2. Unmount it so no RiveView is alive.
3. Mount a new RiveView for the same file and assets.
4. The app crashes while the asset bytes are processed. Intermittent: 4 of 5 automated runs.

What we think happens: RenderContextManager keeps its render contexts weakly ("when no more RiveRenderViews require these, they can be freed"), and RiveFactory holds a raw rive::Factory*. After the last view unmounts the context is freed, and decoding assets for the new view dereferences it.

Tried: decoding on the main thread (same crash, now on the main thread); dropping stale loads with a generation token (still crashes); holding a RiveFile reference (not reliable). RenderContextManager.shared().newDefaultContext() isn't callable from Swift because RenderContext is only forward-declared.