bench(desktop): make --spawn work + capture a real baseline (#67670)

- Resolve the vite CLI via vite/package.json `bin` (Vite 8's exports block
  importing vite/bin/vite.js directly — --spawn failed with ERR_PACKAGE_PATH_NOT_EXPORTED).
- Add a post-launch settle so cold-start contention (vite dep pre-bundling,
  first backend-connect attempts) doesn't contaminate the first scenario.
- Drop the raw autolink from the default stream chunk (resolvable URLs trigger
  link-embed DNS lookups unrelated to render cost).
- Replace seed baseline with real numbers from a darwin-arm64 --spawn run.
  keystroke + transcript are clean; stream is a clean single-run capture (the
  isolated backend may not connect, and its reconnect churn inflates frame
  pacing — re-capture on a connected instance for tighter tolerances).

apps/desktop/scripts/perf/baseline.json

@@ -1,37 +1,37 @@
 {
   "_meta": {
-    "note": "SEED baseline only. Values are approximations from apps/desktop/scripts/profile-typing-lag.md (May 2026, 34MB session, PRE incremental-lex). Run `npm run perf -- --update-baseline` on YOUR reference device to capture real numbers, then commit. Tolerances are intentionally loose until then.",
-    "platform": null,
+    "note": "Captured on darwin-arm64 via `npm run perf -- --spawn`. keystroke + transcript are clean medians. stream = a clean single-run capture; under --spawn the isolated backend may not connect, and its reconnect churn inflates frame-pacing, so re-capture stream on a backend-CONNECTED instance (perf:serve against a live profile, or attach) for tighter tolerances. Re-baseline with `npm run perf -- --update-baseline`.",
+    "platform": "darwin-arm64",
     "node": null,
-    "updated": null
+    "updated": "2026-07-19"
   },
   "scenarios": {
     "stream": {
-      "tolerance": { "tolFrac": 0.5, "tolAbs": 2 },
+      "tolerance": { "tolFrac": 0.6, "tolAbs": 5 },
       "metrics": {
         "longtasks_n": 2,
-        "longtask_max_ms": 127,
-        "frame_p95_ms": 25.6,
-        "frame_p99_ms": 31.4,
-        "slow_frames_33": 6,
-        "intermut_p95_ms": 45
+        "longtask_max_ms": 97,
+        "frame_p95_ms": 18.4,
+        "frame_p99_ms": 28.5,
+        "slow_frames_33": 4,
+        "intermut_p95_ms": 37.1
       }
     },
     "keystroke": {
-      "tolerance": { "tolFrac": 0.5, "tolAbs": 3 },
+      "tolerance": { "tolFrac": 0.6, "tolAbs": 4 },
       "metrics": {
-        "keystroke_p50_ms": 8,
-        "keystroke_p95_ms": 17,
-        "keystroke_p99_ms": 28,
-        "keystroke_slow_16": 6
+        "keystroke_p50_ms": 2.7,
+        "keystroke_p95_ms": 9.9,
+        "keystroke_p99_ms": 17.7,
+        "keystroke_slow_16": 2
       }
     },
     "transcript": {
-      "tolerance": { "tolFrac": 0.5, "tolAbs": 20 },
+      "tolerance": { "tolFrac": 0.75, "tolAbs": 40 },
       "metrics": {
-        "transcript_mount_ms": 450,
-        "transcript_longtask_ms": 350,
-        "transcript_longtask_max_ms": 160
+        "transcript_mount_ms": 287.3,
+        "transcript_longtask_ms": 559,
+        "transcript_longtask_max_ms": 295
       }
     }
   }

apps/desktop/scripts/perf/lib/launch.mjs

@@ -12,7 +12,7 @@
 // spent regardless of the isolated backend.
 
 import { spawn } from 'node:child_process'
-import { copyFileSync, existsSync, mkdtempSync, rmSync } from 'node:fs'
+import { copyFileSync, existsSync, mkdtempSync, readFileSync, rmSync } from 'node:fs'
 import { createRequire } from 'node:module'
 import { homedir, tmpdir } from 'node:os'
 import { dirname, join, resolve } from 'node:path'
@@ -69,6 +69,20 @@ function seedConfigFrom(sourceHome, targetHome) {
   }
 }
 
+// Resolve the vite CLI entry via its package.json `bin` (Vite 8's `exports`
+// blocks importing `vite/bin/vite.js` directly).
+function resolveViteBin() {
+  const pkgPath = require.resolve('vite/package.json')
+  const pkg = JSON.parse(readFileSync(pkgPath, 'utf8'))
+  const rel = typeof pkg.bin === 'string' ? pkg.bin : pkg.bin?.vite
+
+  if (!rel) {
+    throw new Error('could not resolve the vite CLI from vite/package.json')
+  }
+
+  return join(dirname(pkgPath), rel)
+}
+
 function runNode(scriptRelPath, args = []) {
   return new Promise((resolveRun, reject) => {
     const child = spawn(process.execPath, [join(DESKTOP_DIR, scriptRelPath), ...args], {
@@ -99,7 +113,8 @@ export async function startIsolatedInstance({
   hermesHome,
   userDataDir,
   seedConfig = true,
-  bootFakeStepMs = 120
+  bootFakeStepMs = 120,
+  settleMs = 2500
 } = {}) {
   const children = []
   const tempDirs = []
@@ -141,7 +156,7 @@ export async function startIsolatedInstance({
   try {
     // 1. Renderer: reuse an already-running dev server, else start one.
     if (!(await reachable(devUrl))) {
-      const viteBin = require.resolve('vite/bin/vite.js')
+      const viteBin = resolveViteBin()
       const vite = spawn(process.execPath, [viteBin, '--host', '127.0.0.1', '--port', String(devPort)], {
         cwd: DESKTOP_DIR,
         stdio: ['ignore', 'inherit', 'inherit']
@@ -194,6 +209,11 @@ export async function startIsolatedInstance({
       { timeoutMs: 120000, label: 'isolated renderer + __PERF_DRIVE__' }
     )
 
+    // Let cold-start contention (vite dep pre-bundling, first backend-connect
+    // attempts, initial paint) drain before scenarios measure, so numbers
+    // reflect steady state rather than launch noise.
+    await sleep(settleMs)
+
     return {
       cdp,
       devUrl,

apps/desktop/scripts/perf/scenarios/stream.mjs

@@ -113,7 +113,9 @@ export default {
     const tokens = Number(opts.tokens ?? 400)
     const intervalMs = Number(opts.intervalMs ?? 16)
     const flushMinMs = Number(opts.flushMinMs ?? 33)
-    const chunk = opts.chunk ?? '**word** in _italic_ with `code`, a [link](https://x.dev) and prose. '
+    // No raw autolink in the default chunk — a resolvable URL triggers link
+    // embeds / DNS lookups that add noise unrelated to render cost.
+    const chunk = opts.chunk ?? '**word** in _italic_ with `code` and a bit of ordinary prose. '
     const real = Boolean(opts.real)
 
     await cdp.send('Runtime.enable')