fix(client): optimize iOS text presentation handling

src/client/__tests__/useTerminal.test.tsx

@@ -413,7 +413,7 @@ describe('useTerminal', () => {
     })
 
     // Output is wrapped in synchronized output sequences (BSU/ESU)
-    expect(terminal.writes).toEqual([`\x1b[?2026hx\u23FA\uFE0Ey\x1b[?2026l`])
+    expect(terminal.writes).toEqual([`\x1b[?2026hx\u23FAy\x1b[?2026l`])
 
     terminal.selection = ''
 
@@ -444,6 +444,53 @@ describe('useTerminal', () => {
     expect(sendCalls.some((call) => call.type === 'terminal-resize')).toBe(true)
   })
 
+  test('adds text presentation selectors to output on iOS only', async () => {
+    globalAny.navigator = {
+      userAgent: 'iPhone',
+      platform: 'iPhone',
+      maxTouchPoints: 0,
+      clipboard: { writeText: () => Promise.resolve() },
+    } as unknown as Navigator
+
+    const listeners: Array<(message: ServerMessage) => void> = []
+    const { container } = createContainerMock()
+
+    await act(async () => {
+      TestRenderer.create(
+        <TerminalHarness
+          sessionId="session-1"
+          tmuxTarget="agentboard:@1"
+          sendMessage={() => {}}
+          subscribe={(listener) => {
+            listeners.push(listener)
+            return () => {}
+          }}
+          theme={{ background: '#000' }}
+          fontSize={12}
+          onScrollChange={() => {}}
+        />,
+        {
+          createNodeMock: () => container,
+        }
+      )
+    })
+
+    const terminal = TerminalMock.instances[0]
+    if (!terminal) {
+      throw new Error('Expected terminal instance')
+    }
+
+    act(() => {
+      listeners[0]?.({
+        type: 'terminal-output',
+        sessionId: 'session-1',
+        data: `x\u23FAy`,
+      })
+    })
+
+    expect(terminal.writes).toEqual([`\x1b[?2026hx\u23FA\uFE0Ey\x1b[?2026l`])
+  })
+
   test('detaches previous session and cleans up on unmount', async () => {
     globalAny.navigator = {
       userAgent: 'Chrome',

src/client/hooks/useTerminal.ts

@@ -84,23 +84,30 @@ const TEXT_VS = '\uFE0E'
 
 // Characters that iOS Safari renders as emoji but should be text
 // Only add characters here that are verified to cause issues
-const EMOJI_TO_TEXT_CHARS = new Set([
+const EMOJI_TO_TEXT_CHARS = [
   '\u23FA', // ⏺ Black Circle for Record (Claude's bullet)
-])
+] as const
+const escapeRegExp = (value: string) =>
+  value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+const EMOJI_TO_TEXT_REGEX = new RegExp(
+  EMOJI_TO_TEXT_CHARS.map(escapeRegExp).join('|'),
+  'g'
+)
 
 /**
  * Add text presentation selector after characters that iOS renders as emoji.
  * This forces the browser to render them as text glyphs instead.
  */
 export function forceTextPresentation(data: string): string {
-  let result = ''
-  for (const char of data) {
-    result += char
-    if (EMOJI_TO_TEXT_CHARS.has(char)) {
-      result += TEXT_VS
+  // Hot path: most terminal output doesn't contain emoji-like glyphs.
+  // Avoid per-character concatenation (expensive) and skip work when not needed.
+  for (const char of EMOJI_TO_TEXT_CHARS) {
+    if (data.indexOf(char) === -1) {
+      continue
     }
+    return data.replace(EMOJI_TO_TEXT_REGEX, `$&${TEXT_VS}`)
   }
-  return result
+  return data
 }
 
 interface UseTerminalOptions {
@@ -895,7 +902,9 @@ export function useTerminal({
         attachedSession &&
         message.sessionId === attachedSession
       ) {
-        outputBufferRef.current += forceTextPresentation(message.data)
+        outputBufferRef.current += isiOS
+          ? forceTextPresentation(message.data)
+          : message.data
         scheduleFlush()
       }