fix: enable Rust tracing → Android logcat via tracing-android

Rust tracing subscriber was never initialized — all info!/warn!/error!
calls in the engine went to /dev/null. This meant our send/recv health
logging was invisible and we couldn't confirm the congestion fix was
active.

Now initializes tracing-android layer on first nativeInit(), routing
all Rust logs to logcat under tag "wzp_android". Also expanded logcat
filter in DebugReporter to capture engine-level log lines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/wzp/debug/DebugReporter.kt

@@ -138,7 +138,16 @@ class DebugReporter(private val context: Context) {
                     line.contains("AudioFlinger") ||
                     line.contains("DebugReporter") ||
                     line.contains("QUIC") ||
-                    line.contains("quinn")
+                    line.contains("quinn") ||
+                    line.contains("send task") ||
+                    line.contains("recv task") ||
+                    line.contains("send stats") ||
+                    line.contains("recv stats") ||
+                    line.contains("send_media") ||
+                    line.contains("FEC block") ||
+                    line.contains("recv gap") ||
+                    line.contains("frames_dropped") ||
+                    line.contains("opus")
                 }
                 .joinToString("\n")
         } catch (e: Exception) {

crates/wzp-android/Cargo.toml

@@ -28,6 +28,7 @@ libc = "0.2"
 jni = { version = "0.21", default-features = false }
 rand = { workspace = true }
 rustls = { version = "0.23", default-features = false, features = ["ring"] }
+tracing-android = "0.2"
 
 [build-dependencies]
 cc = "1"

crates/wzp-android/src/jni_bridge.rs

@@ -1,6 +1,7 @@
 //! JNI bridge for Android — thin layer between Kotlin and the WzpEngine.
 
 use std::panic;
+use std::sync::Once;
 
 use jni::objects::{JClass, JObject, JString};
 use jni::sys::{jboolean, jint, jlong, jstring};
@@ -28,12 +29,27 @@ fn profile_from_int(value: jint) -> QualityProfile {
     }
 }
 
+static INIT_LOGGING: Once = Once::new();
+
+/// Initialize tracing → Android logcat (tag "wzp_android").
+/// Safe to call multiple times — only the first call takes effect.
+fn init_logging() {
+    INIT_LOGGING.call_once(|| {
+        use tracing_subscriber::layer::SubscriberExt;
+        use tracing_subscriber::util::SubscriberInitExt;
+        if let Ok(layer) = tracing_android::layer("wzp_android") {
+            let _ = tracing_subscriber::registry().with(layer).try_init();
+        }
+    });
+}
+
 #[unsafe(no_mangle)]
 pub unsafe extern "system" fn Java_com_wzp_engine_WzpEngine_nativeInit(
     _env: JNIEnv,
     _class: JClass,
 ) -> jlong {
     let result = panic::catch_unwind(|| {
+        init_logging();
         let handle = Box::new(EngineHandle {
             engine: WzpEngine::new(),
         });