test(mobile): lock quick-commands button stability

Add a focused source-contract test for the always-mounted tab action and confirmed-support sheet gate. Keep the non-obvious safety comment concise, and remove PR screenshots now hosted as GitHub user attachments.

mobile/app/h/[hostId]/session/[worktreeId].tsx

@@ -4514,7 +4514,7 @@ export default function SessionScreen() {
               >
                 <Plus size={16} color={colors.textSecondary} strokeWidth={2.2} />
               </Pressable>
-              {/* Why: always render so the tab row never shifts while capabilities load; the tap explains unsupported/probing hosts instead. Old hosts strip agentPrompt, so the sheet only opens once support is confirmed. */}
+              {/* Why: stable placement matters, while old hosts must stay gated because they strip agentPrompt. */}
               <QuickCommandsTabButton
                 disabled={
                   creating || creatingBrowser || creatingMarkdown || connState !== 'connected'

mobile/src/session/quick-commands-tab-stability-source.test.ts

@@ -0,0 +1,32 @@
+import { readFileSync } from 'node:fs'
+import { describe, expect, it } from 'vitest'
+
+const source = readFileSync(
+  new URL('../../app/h/[hostId]/session/[worktreeId].tsx', import.meta.url),
+  'utf8'
+)
+
+function getQuickCommandsTabSource(): string {
+  const start = source.indexOf('accessibilityLabel="New tab"')
+  expect(start).toBeGreaterThanOrEqual(0)
+  const end = source.indexOf('{/* Content-row host', start)
+  expect(end).toBeGreaterThan(start)
+  return source.slice(start, end)
+}
+
+describe('quick-commands tab stability', () => {
+  it('keeps the button mounted while preserving the capability gate', () => {
+    const tabSource = getQuickCommandsTabSource()
+
+    expect(tabSource).toContain('<QuickCommandsTabButton')
+    expect(tabSource).not.toContain('{quickCommandsSupported === true ?')
+    expect(tabSource).toContain('if (quickCommandsSupported === true)')
+    expect(tabSource).toContain('setShowQuickCommands(true)')
+    expect(tabSource).toContain('Desktop update required for quick commands')
+    expect(tabSource).toContain('Checking desktop capabilities — try again in a moment')
+  })
+
+  it('only presents the sheet after support is confirmed', () => {
+    expect(source).toContain('visible={showQuickCommands && quickCommandsSupported === true}')
+  })
+})