test(terminal): profile webgl render stages

scripts/terminal-bench.mjs

@@ -222,6 +222,9 @@ async function runScenario(browser, options, viewport) {
     frameSamples.push(
       ...(await page.evaluate(() => window.__terminalBenchFrames || [])),
     );
+    const rendererStats = await page.evaluate(() => window.__terminalBench?.webglFrames || []);
+    const cleanProbe = { ...probe };
+    delete cleanProbe.webglFrames;
     const canvasPixelSmoke = await page.evaluate(() => {
       const canvas = document.querySelector("canvas.terminal-canvas:not([hidden])");
       if (!canvas) {
@@ -279,7 +282,8 @@ async function runScenario(browser, options, viewport) {
       elapsedMs,
       rowsPerSecond: round(options.lines / (elapsedMs / 1000)),
       frameMs: summarizeSamples(frameSamples),
-      probe,
+      rendererStats: summarizeRendererStats(rendererStats),
+      probe: cleanProbe,
       pixelSmoke: pixelResult,
       screenshotPath,
     };
@@ -288,6 +292,43 @@ async function runScenario(browser, options, viewport) {
   }
 }
 
+export function summarizeRendererStats(frames) {
+  if (!Array.isArray(frames) || frames.length === 0) {
+    return { count: 0 };
+  }
+  const numericFields = [
+    "totalMs",
+    "syncDomMs",
+    "backdropMs",
+    "collectMs",
+    "backdropTextureMs",
+    "fallbackCanvasMs",
+    "atlasMs",
+    "atlasUploadMs",
+    "vertexBuildMs",
+    "vertexUploadMs",
+    "drawMs",
+    "cells",
+    "atlasEntries",
+    "atlasInsertions",
+    "atlasResets",
+  ];
+  const summary = { count: frames.length };
+  for (const field of numericFields) {
+    const samples = frames
+      .map((frame) => Number(frame[field] || 0))
+      .filter((value) => Number.isFinite(value));
+    summary[field] = summarizeSamples(samples);
+  }
+  summary.fallbackFullCanvasCount = frames.filter(
+    (frame) => Boolean(frame.fallbackFullCanvas),
+  ).length;
+  summary.glyphDrawFailedCount = frames.filter(
+    (frame) => Boolean(frame.glyphDrawFailed),
+  ).length;
+  return summary;
+}
+
 function benchUrl(options) {
   const url = new URL(options.url);
   url.searchParams.set("renderer", options.renderer);