Context

PR #2202 fixed the catalyst body snapshot fetch (corrected the TextureEntry type mismatch), which eliminated the bug where every catalyst fetch was being discarded and falling back to local rendering. However, when catalyst snapshots are unavailable (profile has no snapshots, fetch fails, etc.), the system still falls back to _async_capture_local, which:

1. Instantiates an AvatarPreview scene
2. Re-assembles the full avatar with wearables
3. Renders it off-screen via async_get_viewport_image
4. The viewport rendering (~300ms) still blocks the main thread during capture

While _async_capture_local is marked as async and uses await, the actual rendering operation is synchronous and causes frame hiccups.

Proposed Solution

Implement a proper async/background queue system for avatar profile generation:

Requirements

1. True async rendering — Move the viewport capture off the main thread or use a frame-budgeted approach that spreads rendering across multiple frames
2. Persistent queue — Queue requests for body/face snapshot generation that can be processed in the background
3. Priority system — Visible/nearby avatars get higher priority than distant ones
4. Cache integration — Generated snapshots should be cached with the same key structure as catalyst snapshots
5. Graceful degradation — Impostors should render with a placeholder/silhouette until the snapshot is ready, rather than blocking

Implementation Ideas

• Option A: Render snapshots at reduced resolution (e.g. 128x256 instead of full size) to reduce main-thread time
• Option B: Use multiple small SubViewports and render one avatar part per frame, compositing the final image over several frames
• Option C: Offload to a background Godot instance (server mode) that renders snapshots and returns them via IPC/file
• Option D: Pre-generate snapshots for common avatar configurations during idle time

Related

• Closes Frame hiccups when avatars appear: catalyst body snapshot discarded, impostor always baked locally #2204 (catalyst fetch fixed, but local fallback still blocks)
• Related to [Bug] Review profile generation errors for 829 entities reported by Foundation #1880 (profile generation errors — 829 entities)
• Builds on the impostor system in godot/src/decentraland_components/avatar/impostor/

Benefits

• Eliminates remaining frame hiccups from avatar appearance
• Better UX for users with profiles that lack catalyst snapshots
• More predictable performance in crowded scenes
• Allows for progressive loading of avatar quality

Requested by Mateo via Slack