diff --git a/.gitignore b/.gitignore
index 72afa2e0cc..215f15a3ec 100644
--- a/.gitignore
+++ b/.gitignore
@@ -113,4 +113,4 @@ opencode.json
 /.codex/
 /tools/__pycache__
 /frontend/playwright/perf/results*/
-/frontend/playwright/perf/report.html
+/frontend/playwright/perf/report*.html
diff --git a/frontend/playwright/perf/README.md b/frontend/playwright/perf/README.md
index d895d77f26..c6ee2d7a8d 100644
--- a/frontend/playwright/perf/README.md
+++ b/frontend/playwright/perf/README.md
@@ -27,12 +27,15 @@ Projects: `gpu-memory-chromium`, `gpu-memory-firefox`, `gpu-memory-webkit`.
 | Variable | Default | Meaning |
 |---|---|---|
 | `PERF_LABEL` | `git describe --dirty` | Name of the build under test; results go to `results/<label>/` |
-| `PERF_FIXTURE` | `render-wasm/get-file-shadows.json` | `get-file` fixture under `playwright/data/` |
+| `PERF_FIXTURE` | `render-wasm/get-file-shadows.json` | `get-file` fixture under `playwright/data/`; served over local HTTP, so size is no limit |
 | `PERF_REPEATS` | `3` | Runs per engine; repeat 0 is dropped as warm-up |
 | `PERF_ITERATIONS` | `12` | Steps per phase |
 | `PERF_DPR` | `2` | Device pixel ratio |
+| `PERF_EDIT_TARGET` | select all | `x,y` in CSS px: the edit phase selects the element there instead of everything |
 | `PERF_SKIA_CACHE_MB` | build default | Skia resource cache budget, set after the first render (needs `set_resource_cache_limit_mb` in the wasm build) |
 | `PERF_PURGE_PROBE` | off | `1` calls `free_gpu_resources` at the end and samples again |
+| `PERF_TIMEOUT_MIN` | `15` | Time limit per run; heavy fixtures in Firefox need more |
+| `PERF_TRACE_SIZE` | off | `WxH`: record the call stacks of allocations of that size (in each sample's `web.traces`) |
 | `PERF_PROC_MATCH` | `ms-playwright` | Substring of the browser binary path used to find its processes |
 
 Report flags: `--baseline <label>` (default `develop`, else the oldest
diff --git a/frontend/playwright/perf/gpu-memory.spec.js b/frontend/playwright/perf/gpu-memory.spec.js
index cd9d93739d..6a4d499fc2 100644
--- a/frontend/playwright/perf/gpu-memory.spec.js
+++ b/frontend/playwright/perf/gpu-memory.spec.js
@@ -1,6 +1,8 @@
 import { test } from "@playwright/test";
 import { execFileSync } from "node:child_process";
 import { createHash } from "node:crypto";
+import { createReadStream } from "node:fs";
+import { createServer } from "node:http";
 import { mkdir, readFile, writeFile } from "node:fs/promises";
 import { WasmWorkspacePage } from "../ui/pages/WasmWorkspacePage";
 import { installWebGLMemoryTracker } from "./gpu-memory/webgl-tracker.js";
@@ -23,7 +25,11 @@ const config = {
   iterations: Number(env.PERF_ITERATIONS ?? 12),
   settleMs: Number(env.PERF_SETTLE_MS ?? 300),
   purgeProbe: env.PERF_PURGE_PROBE === "1",
+  // "x,y" in CSS px: select the element there instead of everything. On a
+  // big page, moving every shape at once takes minutes per step.
+  editTarget: env.PERF_EDIT_TARGET?.split(",").map(Number) ?? null,
   skiaCacheMb: env.PERF_SKIA_CACHE_MB ? Number(env.PERF_SKIA_CACHE_MB) : null,
+  timeoutMin: Number(env.PERF_TIMEOUT_MIN ?? 15),
   outDir: env.PERF_OUT_DIR ?? "playwright/perf/results",
 };
 
@@ -52,6 +58,36 @@ async function setPageSize(page, size) {
   }, size);
 }
 
+// Serves the fixture over plain HTTP. `route.fulfill` sends the body through
+// the DevTools protocol, and a large fixture (tens of MB) drops the browser
+// session.
+let fixtureServer;
+
+async function fixtureUrl() {
+  if (!fixtureServer) {
+    fixtureServer = createServer((_req, res) => {
+      res.writeHead(200, {
+        "content-type": "application/transit+json",
+        "access-control-allow-origin": "*",
+      });
+      createReadStream(`playwright/data/${config.fixture}`).pipe(res);
+    });
+    await new Promise((resolve) =>
+      fixtureServer.listen(0, "127.0.0.1", resolve),
+    );
+  }
+  return `http://127.0.0.1:${fixtureServer.address().port}/get-file`;
+}
+
+test.afterAll(() => fixtureServer?.close());
+
+// goToWorkspace waits for the page name, which differs per fixture.
+async function fixturePageName(fixture) {
+  const data = JSON.parse(await readFile(`playwright/data/${fixture}`, "utf8"));
+  const pages = data["~:data"]?.["~:pages-index"] ?? {};
+  return Object.values(pages)[0]?.["~:name"] ?? "Page 1";
+}
+
 async function wasmHash() {
   const bytes = await readFile("resources/public/js/render-wasm.wasm").catch(
     () => null,
@@ -83,10 +119,12 @@ async function settle(page, quietMs = config.settleMs, maxMs = 10000) {
   );
 }
 
-test.describe.configure({ mode: "serial" });
-
 test.beforeEach(async ({ page }) => {
-  await page.addInitScript(installWebGLMemoryTracker);
+  page.on("crash", () => console.error("[gpu-memory] page crashed"));
+  page.on("pageerror", (e) => console.error(`[gpu-memory] ${e.message}`));
+  await page.addInitScript(installWebGLMemoryTracker, {
+    traceSize: env.PERF_TRACE_SIZE ?? null,
+  });
   await WasmWorkspacePage.init(page);
   await WasmWorkspacePage.mockRPC(
     page,
@@ -101,7 +139,7 @@ for (let repeat = 0; repeat < config.repeats; repeat++) {
     browser,
     browserName,
   }, testInfo) => {
-    test.setTimeout(15 * 60 * 1000);
+    test.setTimeout(config.timeoutMin * 60 * 1000);
 
     const workspace = new WasmWorkspacePage(page);
     const dir = `${config.outDir}/${config.label}`;
@@ -120,7 +158,12 @@ for (let repeat = 0; repeat < config.repeats; repeat++) {
 
     await workspace.setupEmptyFile();
     await workspace.mockGetFile(config.fixture);
-    await workspace.goToWorkspace();
+    const url = await fixtureUrl();
+    // Registered last, so it wins over the fulfill route mockGetFile added.
+    await page.route(/get-file\?/, (route) => route.continue({ url }));
+    await workspace.goToWorkspace({
+      pageName: await fixturePageName(config.fixture),
+    });
     await workspace.waitForFirstRenderWithoutUI();
     if (config.skiaCacheMb) {
       // Set after the first render, so the load phase still runs on the
@@ -168,7 +211,12 @@ for (let repeat = 0; repeat < config.repeats; repeat++) {
       await sample("pan", i);
     }
 
-    await page.keyboard.press("ControlOrMeta+a");
+    if (config.editTarget) {
+      const [ex, ey] = config.editTarget;
+      await page.mouse.click(ex, ey);
+    } else {
+      await page.keyboard.press("ControlOrMeta+a");
+    }
     for (let i = 0; i < config.iterations; i++) {
       await page.keyboard.press(i % 2 ? "Shift+ArrowLeft" : "Shift+ArrowRight");
       await sample("edit", i);
@@ -201,6 +249,7 @@ for (let repeat = 0; repeat < config.repeats; repeat++) {
         fixture: config.fixture,
         iterations: config.iterations,
         skiaCacheMb: config.skiaCacheMb,
+        editTarget: config.editTarget,
         viewport: base,
         dpr: testInfo.project.use.deviceScaleFactor ?? 1,
         renderer,
diff --git a/frontend/playwright/perf/gpu-memory/webgl-tracker.js b/frontend/playwright/perf/gpu-memory/webgl-tracker.js
index 65eea42782..28f9a0cc99 100644
--- a/frontend/playwright/perf/gpu-memory/webgl-tracker.js
+++ b/frontend/playwright/perf/gpu-memory/webgl-tracker.js
@@ -5,8 +5,12 @@
 // running totals of the bytes backing textures, renderbuffers and buffers,
 // plus counters for every storage (re)allocation. Sizes are what WebGL was
 // asked for; drivers add padding, alignment and their own copies on top.
-export function installWebGLMemoryTracker() {
+export function installWebGLMemoryTracker(options = {}) {
   if (globalThis.__gpuMem) return;
+  // Allocation size ("WxH") whose call stacks are recorded, for finding
+  // which render path creates it.
+  const traceSize = options.traceSize ?? null;
+  const traces = new Map();
 
   const protos = [
     globalThis.WebGL2RenderingContext?.prototype,
@@ -105,6 +109,14 @@ export function installWebGLMemoryTracker() {
   const allocsBySize = new Map();
 
   function logAlloc(kind, w, h, bytes) {
+    if (traceSize === `${w}x${h}`) {
+      const stack = (new Error().stack ?? "")
+        .split("\n")
+        .slice(3, 30)
+        .map((l) => l.trim())
+        .join("\n");
+      traces.set(stack, (traces.get(stack) ?? 0) + 1);
+    }
     const key = `${kind} ${w}x${h}`;
     const entry = allocsBySize.get(key) ?? { count: 0, bytes: 0 };
     entry.count++;
@@ -443,6 +455,12 @@ export function installWebGLMemoryTracker() {
         },
         allocatedBytesTotal,
         allocsBySize: bySize,
+        traces: traceSize
+          ? [...traces.entries()]
+              .sort((a, b) => b[1] - a[1])
+              .slice(0, 8)
+              .map(([stack, count]) => ({ count, stack }))
+          : undefined,
         contexts: contexts.length,
         contextLosses,
         wasmHeapBytes: wasmHeapBytes(),