perf(android): low-latency decode overhaul — vendor keys, async loop, system tuning

Close the latency gap on the Android client with per-SoC decoder tuning, an
event-driven decode loop, and full system integration.

- Decoder selection: rank MediaCodecList decoders in Kotlin (hardware/vendor
  preferred, software avoided, FEATURE_LowLatency probed) and create the chosen
  one by name. Per-SoC low-latency keys gated on the codec-name prefix: Qualcomm
  picture-order + low-latency, Exynos (also Google Tensor), Amlogic, HiSilicon;
  MediaTek vdec-lowlatency set unconditionally. operating-rate = MAX (Qualcomm)
  vs priority = 0 (else) are mutually exclusive. NVIDIA/Rockchip/Realtek have no
  vendor key — covered by ranking + the standard low-latency key.

- Async decode loop: AMediaCodec async-notify replaces the poll loop, presenting a
  decoded frame the instant it is ready instead of waiting out a poll interval.
  Behind USE_ASYNC_DECODE with the synchronous loop kept for A/B during bring-up.

- System integration: Wi-Fi FULL_LOW_LATENCY lock and HDMI ALLM
  (setPreferMinimalPostProcessing) for the stream's lifetime; game_mode_config.xml
  opting out of OEM downscaling / FPS overrides.

- Pipeline: boost the data-plane pump + audio thread priorities, AAudio usage=Game,
  DSCP marking on by default on Android, ADPF setPreferPowerEfficiency(false),
  and setFrameRateWithChangeStrategy(ALWAYS) to force the HDMI mode switch on TV.

- lowLatencyMode master toggle (default on) as the escape hatch; the stats HUD now
  shows the resolved decoder name.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/native/src/session/planes.rs

@@ -2,20 +2,31 @@
 //! ~1 Hz decode-stats drain for the HUD.
 
 use jni::objects::JObject;
-use jni::sys::{jboolean, jdoubleArray, jlong, jsize};
+// Used only by the android-gated `nativeStartVideo`; on the host build that fn is cfg'd out.
+#[cfg(target_os = "android")]
+use jni::objects::JString;
+use jni::sys::{jboolean, jdoubleArray, jlong, jsize, jstring};
 use jni::JNIEnv;
 
 use super::{jni_guard, SessionHandle};
 
-/// `NativeBridge.nativeStartVideo(handle, surface)` — wrap the SurfaceView's `Surface` as an
-/// `ANativeWindow` and start the HEVC decode thread rendering onto it. No-op if already started.
+/// `NativeBridge.nativeStartVideo(handle, surface, decoderName, lowLatencyMode, lowLatencyFeature)`
+/// — wrap the SurfaceView's `Surface` as an `ANativeWindow` and start the decode thread rendering
+/// onto it. `decoderName` is the codec Kotlin ranked from `MediaCodecList` (`""` = let the platform
+/// resolve the default for the MIME); `lowLatencyMode` is the user's master toggle;
+/// `lowLatencyFeature` is whether that decoder advertised `FEATURE_LowLatency` (HUD label only).
+/// No-op if already started.
 #[cfg(target_os = "android")]
 #[no_mangle]
 pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeStartVideo(
-    env: JNIEnv,
+    mut env: JNIEnv,
     _this: JObject,
     handle: jlong,
     surface: JObject,
+    decoder_name: JString,
+    low_latency_mode: jboolean,
+    ll_feature: jboolean,
+    is_tv: jboolean,
 ) {
     use super::VideoThread;
     use std::sync::atomic::AtomicBool;
@@ -24,6 +35,12 @@ pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeStartVideo(
     if handle == 0 {
         return;
     }
+    // The decoder name Kotlin picked (empty string / read failure ⇒ None ⇒ default resolver).
+    let decoder = env
+        .get_string(&decoder_name)
+        .ok()
+        .map(String::from)
+        .filter(|s| !s.is_empty());
     // SAFETY: live handle per the nativeConnect/nativeClose contract.
     let h = unsafe { &*(handle as *const SessionHandle) };
     let mut guard = h.video.lock().unwrap();
@@ -48,13 +65,67 @@ pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeStartVideo(
     let client = h.client.clone();
     let sd = shutdown.clone();
     let st = h.stats.clone(); // session-lifetime stats (gate survives surface recreate)
+    let opts = crate::decode::DecodeOptions {
+        decoder_name: decoder,
+        ll_feature: ll_feature != 0,
+        low_latency_mode: low_latency_mode != 0,
+        is_tv: is_tv != 0,
+    };
     let join = std::thread::Builder::new()
         .name("pf-decode".into())
-        .spawn(move || crate::decode::run(client, window, sd, st))
+        .spawn(move || crate::decode::run(client, window, sd, st, opts))
         .ok();
     *guard = Some(VideoThread { shutdown, join });
 }
 
+/// `NativeBridge.nativeVideoMime(handle): String` — the MediaCodec MIME for the codec the host
+/// resolved (`"video/hevc"` / `"video/avc"` / `"video/av01"`), so Kotlin can rank `MediaCodecList`
+/// decoders for it before calling [`Java_io_unom_punktfunk_kit_NativeBridge_nativeStartVideo`].
+/// Empty string on a `0` handle. Cheap; safe on the UI thread.
+#[cfg(target_os = "android")]
+#[no_mangle]
+pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeVideoMime<'local>(
+    env: JNIEnv<'local>,
+    _this: JObject<'local>,
+    handle: jlong,
+) -> jstring {
+    jni_guard(std::ptr::null_mut(), || {
+        if handle == 0 {
+            return std::ptr::null_mut();
+        }
+        // SAFETY: live handle per the nativeConnect/nativeClose contract.
+        let h = unsafe { &*(handle as *const SessionHandle) };
+        match env.new_string(crate::decode::codec_mime(h.client.codec)) {
+            Ok(s) => s.into_raw(),
+            Err(_) => std::ptr::null_mut(),
+        }
+    })
+}
+
+/// `NativeBridge.nativeVideoDecoderLabel(handle): String` — the resolved decoder identity for the
+/// HUD, e.g. `c2.qti.avc.decoder · low-latency`, or `""` before the decode thread has resolved one.
+/// One-shot (the decoder is fixed for the session); poll once after the HUD appears. Not
+/// android-gated — pure `jni` + a lock, so it links on the host build too (Kotlin only calls it on
+/// device).
+#[no_mangle]
+pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeVideoDecoderLabel<'local>(
+    env: JNIEnv<'local>,
+    _this: JObject<'local>,
+    handle: jlong,
+) -> jstring {
+    jni_guard(std::ptr::null_mut(), || {
+        if handle == 0 {
+            return std::ptr::null_mut();
+        }
+        // SAFETY: live handle per the nativeConnect/nativeClose contract.
+        let h = unsafe { &*(handle as *const SessionHandle) };
+        match env.new_string(h.stats.decoder_label()) {
+            Ok(s) => s.into_raw(),
+            Err(_) => std::ptr::null_mut(),
+        }
+    })
+}
+
 /// `NativeBridge.nativeStopVideo(handle)` — stop + join the decode thread (without closing the
 /// session). No-op on `0`.
 #[no_mangle]