fix: refine linux voice runtime behavior

crates/chanora_audio/src/engine.rs

@@ -1774,11 +1774,11 @@ impl AudioEngine {
     }
 
     /// Latest Android voice-audio diagnostics snapshot (SDD-112 item
-    /// 10 / SDD-113 item 7 / SDD-116 item 3). On non-Android targets
-    /// this always returns `None`. On Android it returns `Some(...)`
+    /// 10 / SDD-113 item 7 / SDD-116 item 3). Returns `Some(...)`
     /// once `AndroidVoiceUnit::open()` has published a snapshot; the
-    /// slot is cleared on `close()` / `Drop`. Per SDD-090 the
-    /// snapshot contains only device-side technical scalars — no PII.
+    /// slot is cleared on `close()` / `Drop`. Per SDD-090 the snapshot
+    /// contains only device-side technical scalars — no PII.
+    #[cfg(target_os = "android")]
     pub fn android_diagnostics(
         &self,
     ) -> Option<crate::mobile_voice_backend::AndroidAudioDiagnostics> {