feat(webgl): handle WebGL context loss

[chiefcll]

Summary

On low-RAM devices running Chromium 123+, the GPU context is dropped when the app is backgrounded for >5s (Chromium change 5285836). After that, gl.createTexture() and friends return null and the engine crashes — common on Android TV / Fire TV. This adds pragmatic core handling for WebGL context loss, mirroring the approach settled on in rdkcentral/Lightning#469.

What changed

• Listener (WebGlRenderer): attach a webglcontextlost listener on the canvas that notifies the Stage.
• Loop halt (WebPlatform): once the context is lost, runLoop issues no GL calls and stops rescheduling itself, so the engine never touches a dead context.
• Stage state + event (Stage): a one-way isContextLost latch and setContextLost(), which emits contextLost on the event bus.
• Public event type (RendererMain): RendererMainContextLostEvent + @fires docs, so renderer.on('contextLost', …) is typed.
• Docs (BROWSERS.md): new "WebGL Context Loss" section with the recommended app-side handler.

renderer.on('contextLost', () => window.location.reload());

Design note: no restore path

We deliberately do not call event.preventDefault() on webglcontextlost (the browser's request-to-restore signal) and do not listen for webglcontextrestored. The engine cannot rebuild its GPU resources (textures, programs, buffers) in place — an earlier draft resumed the loop on restore, which would have rendered against dead handles. Since the supported recovery is an app reload, opting into restoration would only leave a non-reloading consumer with a frozen app on a fresh-but-empty context. Full in-engine recovery (re-fetching texture sources, recompiling programs, re-uploading) is intentionally out of scope; the draw loop is already crash-safe via the existing bindTextures guard.

Test plan

• pnpm test — full unit suite passes (232 tests, incl. new Stage.contextLoss.test.ts and WebPlatform.contextLoss.test.ts)
• pnpm build — tsc clean
• prettier + eslint clean on changed files (0 errors)
• Reviewer: verify on a real low-RAM target / simulate via gl.getExtension('WEBGL_lose_context').loseContext()

🤖 Generated with Claude Code

[andrewgerez]

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