WebGPU pixel look: GPU colours the world, CPU only rare cells (t88 phase 2a)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/test_perf.py

@@ -38,6 +38,7 @@ def main():
         pg.on('pageerror', lambda e: errors.append(str(e)))
         pg.add_init_script('window.requestAnimationFrame = () => 0;')
         pg.goto(url)
+        pg.evaluate('CAPS_CHECK')
         pg.add_script_tag(content=(ROOT / 'tools/perf-scenes.js').read_text())
         assert pg.evaluate('crossOriginIsolated')
         # Compare to the unwrapped functions, and hash the byte representation of all grid state.
@@ -66,8 +67,8 @@ def main():
               performance.now = () => 5000;
               R.rain = rainAt(Math.max(0, Math.min(W - 1, Math.floor(R.camX + R.bw / 2))));
               try {
-                PERF_MARKS = false; drawWorld(); const a = R.canvas.toDataURL();
-                PERF_MARKS = true; drawWorld(); const b = R.canvas.toDataURL();
+                PERF_MARKS = false; drawWorld(); const a = worldPixelContext().canvas.toDataURL();
+                PERF_MARKS = true; drawWorld(); const b = worldPixelContext().canvas.toDataURL();
                 return a === b;
               } finally { PERF_MARKS = false; performance.now = now; }
             }''', look)