fix(viewer): drive the frame loop with a timer when ?disable=draw (#483)

With no real frames submitted, Chromium's no-damage scheduler throttles
requestAnimationFrame to 1Hz on Linux — measured in the headless bake
worker: every useFrame system ticked once per second, so a heavy scene
needed 300+ seconds of wall time just to run ~300 frames of build work
(and exceeded the capture deadline on the worker's slower cores). The
empty-scene clear from #482 avoids this on macOS but not on Linux.

When `draw` is disabled, drive advance() with setInterval instead of
rAF — plain timers are never throttled on a visible page, so the loop
pacing is deterministic (fps prop) regardless of compositor heuristics.
Normal rendering paths are untouched.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/viewer/src/components/viewer/frame-limiter.tsx

@@ -6,6 +6,20 @@ type FrameLimiterProps = {
   fps?: number
 }
 
+// `?disable=draw` (see post-processing.tsx): the page renders no real frames,
+// and Chromium's no-damage scheduler then throttles requestAnimationFrame to
+// 1Hz on Linux (measured in the headless bake worker — every useFrame system
+// ticked once per second and a heavy scene took 300+ seconds to settle). A
+// plain timer is never throttled on a visible page, so drive the loop with
+// setInterval instead of rAF when nothing is drawn.
+const DRAW_DISABLED =
+  typeof window !== 'undefined' &&
+  new Set(
+    (new URLSearchParams(window.location.search).get('disable') ?? '')
+      .split(',')
+      .map((s) => s.trim()),
+  ).has('draw')
+
 const FrameLimiter: React.FC<FrameLimiterProps> = ({ fps = 50 }) => {
   const { advance, set, frameloop: initFrameloop, scene, clock } = useThree()
   const renderer = useThree((state) => state.gl)
@@ -18,6 +32,7 @@ const FrameLimiter: React.FC<FrameLimiterProps> = ({ fps = 50 }) => {
     let then = 0
     let i = 0
     let raf: number | null = null
+    let timer: ReturnType<typeof setInterval> | null = null
     const interval = 1000 / fps
     function tick(t: DOMHighResTimeStamp) {
       raf = requestAnimationFrame(tick)
@@ -30,13 +45,23 @@ const FrameLimiter: React.FC<FrameLimiterProps> = ({ fps = 50 }) => {
     }
     // Set frameloop to never, it will shut down the default render loop
     set({ frameloop: 'never' })
-    // Kick off custom render loop
-    raf = requestAnimationFrame(tick)
+    if (DRAW_DISABLED) {
+      timer = setInterval(() => {
+        i += interval / 1000
+        advance(i)
+      }, interval)
+    } else {
+      // Kick off custom render loop
+      raf = requestAnimationFrame(tick)
+    }
     // Restore initial setting
     return () => {
       if (raf) {
         cancelAnimationFrame(raf)
       }
+      if (timer) {
+        clearInterval(timer)
+      }
       set({ frameloop: initFrameloop })
     }
   }, [fps, advance, set, initFrameloop, renderPaused])