perf(desktop): add model-picker open-latency probes

probe-model-picker.mjs times pill-click → menu painted over N rounds;
profile-model-picker.mjs wraps one open in a CPU profile with a
top-self-time table. Both attach to the perf:serve instance.

apps/desktop/scripts/probe-model-picker.mjs

@@ -0,0 +1,80 @@
+// Model picker open latency probe: click the composer model pill, time until
+// the dropdown/dialog content paints, repeat. Run with --cpuprofile via the
+// harness runner once promoted; standalone for iteration.
+//   node scripts/perf/probe-model-picker.mjs [--port 9222] [--rounds 5]
+import { CDP } from './perf/lib/cdp.mjs'
+
+const args = process.argv.slice(2)
+const flag = name => {
+  const i = args.indexOf(`--${name}`)
+  return i >= 0 ? args[i + 1] : undefined
+}
+const port = Number(flag('port') ?? 9222)
+const rounds = Number(flag('rounds') ?? 5)
+const sleep = ms => new Promise(r => setTimeout(r, ms))
+
+const cdp = await CDP.connect({ port })
+await cdp.send('Runtime.enable')
+
+// Find the pill (dropdown path) — the composer model selector button.
+const PILL = `(() => {
+  const btns = [...document.querySelectorAll('button[aria-label]')]
+  const pill = btns.find(b => /model/i.test(b.getAttribute('aria-label') || '') && b.closest('[data-slot]'))
+  return pill ? (pill.getAttribute('aria-label') || 'found') : null
+})()`
+
+console.log('pill:', await cdp.eval(PILL))
+
+const MEASURE = `
+  (async () => {
+    const btns = [...document.querySelectorAll('button[aria-label]')]
+    const pill = btns.find(b => /model/i.test(b.getAttribute('aria-label') || ''))
+    if (!pill) return JSON.stringify({ error: 'no pill' })
+
+    const t0 = performance.now()
+    pill.dispatchEvent(new PointerEvent('pointerdown', { bubbles: true }))
+    pill.dispatchEvent(new PointerEvent('pointerup', { bubbles: true }))
+    pill.click()
+
+    // Wait for menu/dialog content to exist AND paint (double rAF after found).
+    const found = await new Promise(resolve => {
+      const deadline = performance.now() + 5000
+      const check = () => {
+        const menu = document.querySelector('[role="menu"], [role="dialog"] [cmdk-list]')
+        if (menu && menu.childElementCount > 0) {
+          requestAnimationFrame(() => requestAnimationFrame(() => resolve(performance.now())))
+          return
+        }
+        if (performance.now() > deadline) { resolve(null); return }
+        requestAnimationFrame(check)
+      }
+      check()
+    })
+
+    const openMs = found ? found - t0 : null
+    const rows = document.querySelectorAll('[role="menu"] [role="menuitem"], [cmdk-item]').length
+
+    // Close: Escape.
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }))
+    const menu = document.querySelector('[role="menu"], [role="dialog"]')
+    menu?.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }))
+    await new Promise(r => setTimeout(r, 300))
+
+    return JSON.stringify({ openMs, rows })
+  })()
+`
+
+const samples = []
+
+for (let i = 0; i < rounds; i++) {
+  const raw = await cdp.eval(MEASURE, { awaitPromise: true })
+  const r = JSON.parse(raw)
+  console.log(`round ${i}:`, r)
+  if (typeof r.openMs === 'number') samples.push(r.openMs)
+  await sleep(500)
+}
+
+samples.sort((a, b) => a - b)
+console.log('\nopen latency ms — min/median/max:',
+  Math.round(samples[0]), '/', Math.round(samples[Math.floor(samples.length / 2)]), '/', Math.round(samples.at(-1)))
+cdp.close()

apps/desktop/scripts/profile-model-picker.mjs

@@ -0,0 +1,60 @@
+// CPU-profile one model-picker open.
+//   node scripts/profile-model-picker.mjs [--port 9222]
+import { writeFileSync } from 'node:fs'
+
+import { CDP } from './perf/lib/cdp.mjs'
+import { cpuProfileTopSelf } from './perf/lib/stats.mjs'
+
+const port = Number(process.argv.includes('--port') ? process.argv[process.argv.indexOf('--port') + 1] : 9222)
+const cdp = await CDP.connect({ port })
+await cdp.send('Runtime.enable')
+await cdp.send('Profiler.enable')
+await cdp.send('Profiler.setSamplingInterval', { interval: 100 })
+
+const OPEN = `
+  (async () => {
+    // Reset: close any open menu first.
+    document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }))
+    await new Promise(r => setTimeout(r, 250))
+
+    const btns = [...document.querySelectorAll('button[aria-label]')]
+    const pill = btns.find(b => /model/i.test(b.getAttribute('aria-label') || ''))
+    if (!pill) return -1
+    const t0 = performance.now()
+    pill.dispatchEvent(new PointerEvent('pointerdown', { bubbles: true }))
+    pill.dispatchEvent(new PointerEvent('pointerup', { bubbles: true }))
+    pill.click()
+    const found = await new Promise(resolve => {
+      const deadline = performance.now() + 8000
+      const check = () => {
+        const menu = document.querySelector('[role="menu"]')
+        if (menu && menu.childElementCount > 0) {
+          requestAnimationFrame(() => requestAnimationFrame(() => resolve(performance.now())))
+          return
+        }
+        if (performance.now() > deadline) { resolve(-1); return }
+        requestAnimationFrame(check)
+      }
+      check()
+    })
+    return found < 0 ? -1 : found - t0
+  })()
+`
+
+await cdp.send('Profiler.start')
+const openMs = await cdp.eval(OPEN)
+const { profile } = await cdp.send('Profiler.stop')
+
+console.log('openMs:', Math.round(openMs))
+const out = `/tmp/model-picker-open.cpuprofile`
+writeFileSync(out, JSON.stringify(profile))
+console.log('wrote', out)
+console.log('top self-time (ms):')
+
+for (const r of cpuProfileTopSelf(profile, 20)) {
+  console.log(`  ${r.ms.toFixed(1).padStart(7)}  ${r.name.padEnd(44)}  ${r.url.split('/').slice(-2).join('/')}:${r.line}`)
+}
+
+// Close the menu again.
+await cdp.eval(`document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }))`)
+cdp.close()