feat(voice): harden Android audio and channel joins

crates/chanora_audio/src/lib.rs

@@ -52,7 +52,7 @@ pub use engine::{AudioEngine, AudioEngineConfig};
 // bench harness under `crates/chanora_audio/benches/` can construct a
 // CaptureState and drive `ingest` without re-implementing the engine.
 // Not part of the supported public API.
-#[cfg(not(target_os = "ios"))]
+#[cfg(not(any(target_os = "ios", target_os = "android")))]
 #[doc(hidden)]
 pub use engine::bench_seam;
 pub use ptt::{AudioTransmitGate, MissedKeyUpWatchdog, PttBackendDescriptor, PttCapabilityLevel};
@@ -84,6 +84,11 @@ pub enum AudioError {
     /// A backend-specific failure surfaced without a typed mapping.
     #[error("audio backend: {0}")]
     Backend(String),
+    /// Android platform not ready — ndk_context not initialised before
+    /// audio engine start. This occurs when `initChanoraContext` has not
+    /// been called before `voice_join` triggers the audio engine.
+    #[error("android platform not ready: ndk_context not initialised")]
+    PlatformNotReady,
 }
 
 /// Audio-effect toggles. Defaults match DEC-007 (AEC),