Opt-In Completion Ding when Codex is Idle

What feature would you like to see?

I’d like an optional, experimental feature that plays a subtle terminal bell when a turn completes and Codex is waiting for input. This helps when multitasking or when output finishes off‑screen, and provides a lightweight “ready for next prompt” cue without changing UI layout.

Proposed behavior:

• Feature flag, default off (e.g., [features].prompt_complete_ding = true).
• Trigger only when a turn finishes and no queued user input auto‑starts a new turn.
• TUI only, emits a standard terminal bell (BEL / \x07).
• Exposed in /experimental menu with a short name/description.
• Should be safe/no‑op on terminals that ignore the bell.

Additional information

Use cases: waiting for long‑running prompts while focused in another window, or running Codex alongside other terminal tabs.