[BUG] Ctrl+Z suspend not working (macOS iTerm2)

Describe the bug

Ctrl+Z no longer suspends Claude Code CLI. Pressing Ctrl+Z does nothing - the process remains in foreground instead of suspending.

To reproduce

1. Open iTerm2 on macOS
2. Run claude to start Claude Code CLI
3. Press Ctrl+Z
4. Expected: Process suspends, shows [1]+ Stopped claude, returns to shell prompt
5. Actual: Nothing happens, Ctrl+Z is ignored

Environment

• Claude Code version: 2.1.2
• OS: macOS 26.2 (Build 25C56)
• Terminal: iTerm2
• Shell: zsh

Verification done

• Terminal susp is set correctly: stty -a | grep susp shows susp = ^Z
• No iTerm2 key binding overrides for ^Z (checked both global Keys > Key Bindings and Profiles > Keys > Key Bindings - both empty/no ^Z)
• Ctrl+Z works for other processes (e.g., sleep 100 suspends correctly)

Previous behavior

Ctrl+Z suspend was implemented in v1.0.44 (#588) and worked in earlier versions.

Related issues

• #588 - Original implementation of Ctrl+Z suspend (CLOSED - COMPLETED)
• #11898 - iTerm2 TTY/focus issues (possibly related)