[stack 4/4] Reduce realtime self-interruptions during playback (#14827)

## Stack Position
4/4. Top-of-stack sibling built on #14830.

## Base
- #14830

## Sibling
- #14829

## Scope
- Gate low-level mic chunks while speaker playback is active, while
still allowing spoken barge-in.

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/tui/src/lib.rs

@@ -140,6 +140,7 @@ mod voice {
     use std::sync::Mutex;
     use std::sync::atomic::AtomicBool;
     use std::sync::atomic::AtomicU16;
+    use std::sync::atomic::AtomicUsize;
 
     pub struct RecordedAudio {
         pub data: Vec<i16>,
@@ -158,7 +159,11 @@ mod voice {
             Err("voice input is unavailable in this build".to_string())
         }
 
-        pub fn start_realtime(_config: &Config, _tx: AppEventSender) -> Result<Self, String> {
+        pub fn start_realtime(
+            _config: &Config,
+            _tx: AppEventSender,
+            _playback_queued_samples: Arc<AtomicUsize>,
+        ) -> Result<Self, String> {
             Err("voice input is unavailable in this build".to_string())
         }
 
@@ -198,7 +203,10 @@ mod voice {
     }
 
     impl RealtimeAudioPlayer {
-        pub(crate) fn start(_config: &Config) -> Result<Self, String> {
+        pub(crate) fn start(
+            _config: &Config,
+            _queued_samples: Arc<AtomicUsize>,
+        ) -> Result<Self, String> {
             Err("voice output is unavailable in this build".to_string())
         }