refactor(android): split session JNI into modules, HUD-gated stats, AAudio open retry

- native: the 756-line session.rs becomes session/{mod,connect,input,planes}.rs
  around a SessionHandle (connect lifecycle + trust, input plane shims, plane
  start/stop + stats drain).
- Decode-stats sampling is HUD-gated (nativeSetVideoStatsEnabled): with the
  overlay hidden the decode thread skips the per-AU clock read + lock; enabling
  resets the measurement window.
- audio: the AAudio open path is a per-sharing-mode try_open closure — the
  realtime callback state (ring, prime, free-list) is rebuilt per attempt, so a
  failed exclusive-mode try can't leak state into the shared-mode retry.
- Kotlin: ConnectScreen/StreamScreen slimmed by extracting ConnectDialogs,
  StatsOverlay and TouchInput.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -0,0 +1,124 @@
+//! Session lifecycle + plane wiring over JNI.
+//!
+//! A connected session is a [`SessionHandle`] — an `Arc<NativeClient>` plus the decode thread it
+//! feeds — boxed and handed to Kotlin as an opaque `jlong`. The connector is `Sync`, so the decode
+//! thread pulls the video plane (`next_frame`) directly while Kotlin still holds the handle.
+//!
+//! Wired: connect/close, the video plane (HEVC `next_frame` → NDK AMediaCodec → the SurfaceView's
+//! `ANativeWindow`, see [`crate::decode`]), host→client audio ([`crate::audio`]), input
+//! (`send_input` — mouse/keyboard/gamepad), rumble/DualSense HID feedback ([`crate::feedback`]),
+//! and the trust surface: `nativeGenerateIdentity` (persistent identity, Keystore-wrapped on the
+//! Kotlin side), `nativeConnect` with identity + pin (TOFU / pinned), and `nativePair` (SPAKE2 PIN).
+//!
+//! Split by concern: [`connect`] (identity + connect/close + the trust surface), [`planes`]
+//! (video/audio/mic start/stop + the stats drain), [`input`] (the input-plane shims). This module
+//! keeps the shared infrastructure they all deref through.
+//!
+//! TODO(M4 Android stage 1): client→host DualSense rich input (`send_rich_input`), mode
+//! renegotiation. Port the remaining orchestration from `clients/linux`.
+
+mod connect;
+mod input;
+mod planes;
+
+use punktfunk_core::client::NativeClient;
+use std::panic::AssertUnwindSafe;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex};
+use std::thread::JoinHandle;
+
+/// Run a JNI body, catching any panic at the FFI boundary and returning `default` instead.
+///
+/// A panic unwinding out of an `extern "system"` function aborts the whole process on Rust ≥ 1.81 —
+/// a hard crash of the embedding Android app with no logcat trace. This mirrors the discipline the C
+/// ABI already enforces (`punktfunk_core::abi` wraps every entry point in `catch_unwind`); the
+/// `panic = "unwind"` profile in the workspace `Cargo.toml` exists precisely so these guards work.
+/// We apply it to the teardown + background-thread shims (the "leaving a stream" path), where an
+/// unexpected panic (e.g. a poisoned `Mutex` during concurrent teardown) must degrade to a logged
+/// no-op rather than kill the app.
+pub(crate) fn jni_guard<T>(default: T, f: impl FnOnce() -> T) -> T {
+    std::panic::catch_unwind(AssertUnwindSafe(f)).unwrap_or_else(|_| {
+        log::error!("punktfunk JNI: caught a panic at the FFI boundary (returning default)");
+        default
+    })
+}
+
+/// A live session behind the `jlong` handle: the connector + the decode thread it feeds.
+pub(crate) struct SessionHandle {
+    // Read only by the android decode path (`nativeStartVideo` → `crate::decode`); on the host
+    // build (CI's workspace clippy/build) those readers are cfg'd out, so it's intentionally unused.
+    #[cfg_attr(not(target_os = "android"), allow(dead_code))]
+    pub client: Arc<NativeClient>,
+    /// Live decode stats, written by the decode thread and drained ~1 Hz by `nativeVideoStats`.
+    /// Session-lifetime (not per `VideoThread`) so the HUD's enable gate set via
+    /// `nativeSetVideoStatsEnabled` survives surface teardown/recreate and can land before
+    /// `nativeStartVideo` — enabling resets the window, so no stale data leaks across restarts.
+    pub stats: Arc<crate::stats::VideoStats>,
+    video: Mutex<Option<VideoThread>>,
+    #[cfg(target_os = "android")]
+    audio: Mutex<Option<crate::audio::AudioPlayback>>,
+    #[cfg(target_os = "android")]
+    mic: Mutex<Option<crate::mic::MicCapture>>,
+}
+
+struct VideoThread {
+    shutdown: Arc<AtomicBool>,
+    join: Option<JoinHandle<()>>,
+}
+
+impl SessionHandle {
+    /// Signal the decode thread to stop and join it. Idempotent.
+    fn stop_video(&self) {
+        if let Some(mut vt) = self.video.lock().unwrap().take() {
+            vt.shutdown.store(true, Ordering::SeqCst);
+            if let Some(j) = vt.join.take() {
+                let _ = j.join();
+            }
+        }
+    }
+
+    /// Stop + close audio playback. Dropping the [`crate::audio::AudioPlayback`] joins its decode
+    /// thread and closes the AAudio stream. Idempotent.
+    #[cfg(target_os = "android")]
+    fn stop_audio(&self) {
+        let _ = self.audio.lock().unwrap().take();
+    }
+
+    /// Stop mic uplink. Dropping the [`crate::mic::MicCapture`] joins its encode thread and closes
+    /// the AAudio input stream. Idempotent.
+    #[cfg(target_os = "android")]
+    fn stop_mic(&self) {
+        let _ = self.mic.lock().unwrap().take();
+    }
+}
+
+impl Drop for SessionHandle {
+    fn drop(&mut self) {
+        self.stop_video();
+        #[cfg(target_os = "android")]
+        self.stop_audio();
+        #[cfg(target_os = "android")]
+        self.stop_mic();
+    }
+}
+
+/// SHA-256 fingerprint → 64 lowercase hex chars (matches the host log + client-rs).
+fn hex32(fp: &[u8; 32]) -> String {
+    use std::fmt::Write;
+    fp.iter().fold(String::with_capacity(64), |mut s, b| {
+        let _ = write!(s, "{b:02x}");
+        s
+    })
+}
+
+/// 64-hex → [u8; 32]; `None` on bad length/char.
+fn parse_hex32(s: &str) -> Option<[u8; 32]> {
+    if s.len() != 64 {
+        return None;
+    }
+    let mut out = [0u8; 32];
+    for (i, b) in out.iter_mut().enumerate() {
+        *b = u8::from_str_radix(&s[2 * i..2 * i + 2], 16).ok()?;
+    }
+    Some(out)
+}