vc=21: seamless background-audio handoff on 🎧 + HOME

vc=20 fixed channel videos but left two player rough edges that a tester
called out on the phone:

  * Tapping 🎧 (background audio) restarted the stream from the
    beginning instead of picking up where the foreground player was.
  * Pressing HOME on the player auto-entered Picture-in-Picture; what
    a tester wants is seamless background audio.

Both paths now share one handoff: capture exoPlayer.currentPosition,
stop the activity player, start PlaybackService with EXTRA_POSITION_MS,
and seekTo(position) on setMediaItem. Verified on emulator: 🎧 tap from
~34s in-track resumes service at position=34821ms.

HOME-on-player triggers the same path via StrawActivity.onUserLeaveHint
→ PlayerLeaveHandler.handler (a tiny registry the active PlayerScreen
registers in a DisposableEffect; cleared on dispose so the hook is a
no-op anywhere else in the app). The previous DisposableEffect that
called setAutoEnterEnabled(true) is gone; manual PiP via the ⊟ overlay
button stays — that one is still useful and user-triggered.

Also fixes a latent IllegalStateException that the new HOME path
exposed: PlaybackService and PlayerScreen both built MediaSession with
the default empty ID, which the system rejects when both live in the
same process. Service now sets .setId("straw-bg") so the two
sessions can coexist during the brief activity-vs-service overlap
during handoff.

Smoke (emulator 1440x3040):
  * Subscriptions feed renders (vc=20 fix carries over).
  * 🎧 from ~34s in NCS / Different Heaven → service playing
    position=34821ms, no session-ID crash.
  * HOME from PlayerScreen → focus moves to NexusLauncher,
    PlaybackService running with isForeground=true,
    pictureInPictureParams=null on the activity (no PiP).

buildSrc/src/main/kotlin/ProjectConfig.kt

@@ -16,6 +16,14 @@ const val NEWPIPE_APPLICATION_ID_NEW = "net.newpipe.app"
 
 // Sulkta fork — Straw
 //
+// vc=21 / 0.1.0-AG — player hand-off polish:
+//   * 🎧 background-audio button now captures the current position and
+//     resumes the foreground service from there instead of restarting.
+//   * HOME / recents button while on the player now hands off seamlessly
+//     to background audio (same position-preserving path) instead of
+//     auto-entering Picture-in-Picture. Manual PiP via the ⊟ overlay
+//     button is unchanged.
+//
 // vc=20 / 0.1.0-AF — channel-videos fix on top of the rust pipeline
 // cutover. vc=19 returned empty subscription feeds because
 // strawcore-core's channel_info wasn't doing the second browse for the
@@ -24,6 +32,6 @@ const val NEWPIPE_APPLICATION_ID_NEW = "net.newpipe.app"
 // vc=19 / 0.1.0-AE — rust pipeline cutover. Extraction via
 // strawcore-core (Sulkta-OSS/strawcore) via the UniFFI wrapper; no
 // NewPipeExtractor in the runtime path.
-const val STRAW_VERSION_CODE = 20
+const val STRAW_VERSION_CODE = 21
-const val STRAW_VERSION_NAME = "0.1.0-AF"
+const val STRAW_VERSION_NAME = "0.1.0-AG"
 const val STRAW_APPLICATION_ID = "com.sulkta.straw"

strawApp/src/main/kotlin/com/sulkta/straw/StrawActivity.kt

@@ -21,6 +21,7 @@ import androidx.compose.runtime.DisposableEffect
 import androidx.compose.ui.Modifier
 import com.sulkta.straw.feature.channel.ChannelScreen
 import com.sulkta.straw.feature.detail.VideoDetailScreen
+import com.sulkta.straw.feature.player.PlayerLeaveHandler
 import com.sulkta.straw.feature.player.PlayerScreen
 import com.sulkta.straw.feature.search.SearchScreen
 import com.sulkta.straw.feature.settings.SettingsScreen
@@ -109,6 +110,16 @@ class StrawActivity : ComponentActivity() {
         }
     }
 
+    /**
+     * HOME / recents → seamless hand-off to background audio when the
+     * player screen is active. PlayerScreen registers the handler; any
+     * other screen leaves it null and home behaves normally.
+     */
+    override fun onUserLeaveHint() {
+        super.onUserLeaveHint()
+        PlayerLeaveHandler.handler?.invoke()
+    }
+
     /** Pull a YouTube URL out of an incoming Intent (VIEW or SEND). */
     private fun pickYouTubeUrl(intent: Intent?): String? {
         intent ?: return null

strawApp/src/main/kotlin/com/sulkta/straw/feature/player/PlaybackService.kt

@@ -101,7 +101,12 @@ class PlaybackService : MediaSessionService() {
             PendingIntent.FLAG_IMMUTABLE,
         )
 
+        // Distinct session ID so we don't collide with the activity-side
+        // MediaSession (also in this process) when the user hands off from
+        // PlayerScreen → background audio. Default ID is "" which throws
+        // IllegalStateException("Session ID must be unique. ID=").
         mediaSession = MediaSession.Builder(this, player)
+            .setId(MEDIA_SESSION_ID)
             .setSessionActivity(sessionActivityIntent)
             .build()
     }
@@ -122,6 +127,7 @@ class PlaybackService : MediaSessionService() {
         val url = intent?.getStringExtra(EXTRA_URL)?.takeIf { isAllowedAudioUrl(it) }
         val title = intent?.getStringExtra(EXTRA_TITLE)
         val uploader = intent?.getStringExtra(EXTRA_UPLOADER)
+        val startPositionMs = intent?.getLongExtra(EXTRA_POSITION_MS, 0L)?.coerceAtLeast(0L) ?: 0L
         val player = mediaSession?.player
         if (url == null || player == null) {
             // HIGH-2: nothing to play (likely a re-launch with null intent
@@ -139,7 +145,7 @@ class PlaybackService : MediaSessionService() {
                     .build(),
             )
             .build()
-        player.setMediaItem(item)
+        player.setMediaItem(item, startPositionMs)
         player.prepare()
         player.playWhenReady = true
         return START_NOT_STICKY
@@ -231,8 +237,10 @@ class PlaybackService : MediaSessionService() {
         const val EXTRA_URL = "com.sulkta.straw.extra.URL"
         const val EXTRA_TITLE = "com.sulkta.straw.extra.TITLE"
         const val EXTRA_UPLOADER = "com.sulkta.straw.extra.UPLOADER"
+        const val EXTRA_POSITION_MS = "com.sulkta.straw.extra.POSITION_MS"
 
         private const val NOTIF_CHANNEL_ID = "straw.playback"
         private const val NOTIF_ID = 4242
+        private const val MEDIA_SESSION_ID = "straw-bg"
     }
 }

strawApp/src/main/kotlin/com/sulkta/straw/feature/player/PlayerLeaveHandler.kt

@@ -0,0 +1,17 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Sulkta
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * Bridge between StrawActivity.onUserLeaveHint() (HOME / recents button)
+ * and the active PlayerScreen. When the user leaves the player by pressing
+ * HOME, we want a seamless hand-off to the background-audio foreground
+ * service — not Picture-in-Picture. PlayerScreen registers a handler on
+ * compose, clears it on dispose; the activity calls it from the OS hook.
+ */
+
+package com.sulkta.straw.feature.player
+
+object PlayerLeaveHandler {
+    @Volatile
+    var handler: (() -> Unit)? = null
+}

strawApp/src/main/kotlin/com/sulkta/straw/feature/player/PlayerScreen.kt

@@ -135,29 +135,29 @@ fun PlayerScreen(
         }
     }
 
-    // PiP setup: on Android 12+ tell the OS this activity can auto-enter
+    // Home / recents button → seamless hand-off to background audio service
-    // PiP, so when the user presses Home or swipes away the video shrinks
+    // instead of Picture-in-Picture. PiP is still available manually via the
-    // into a floating window instead of pausing/exiting. Aspect ratio is
+    // ⊟ overlay button. We register a handler that the activity calls from
-    // set eagerly so the system can sample it before the first transition.
+    // onUserLeaveHint(); the handler captures currentPosition so the audio
-    val activity = context as? Activity
+    // service resumes from the same point. Same code path that the explicit
-    DisposableEffect(activity) {
+    // 🎧 button uses.
-        if (activity != null && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+    val resolvedState = androidx.compose.runtime.rememberUpdatedState(state.resolved)
-            val params = PictureInPictureParams.Builder()
+    DisposableEffect(Unit) {
-                .setAspectRatio(Rational(16, 9))
+        PlayerLeaveHandler.handler = handler@{
-                .setAutoEnterEnabled(true)
+            val r = resolvedState.value ?: return@handler
-                .build()
+            val audio = r.audioUrl ?: r.combinedUrl ?: return@handler
-            runCatching { activity.setPictureInPictureParams(params) }
+            val position = exoPlayer.currentPosition.coerceAtLeast(0L)
-        }
+            runCatching { exoPlayer.stop() }
-        onDispose {
+            runCatching { exoPlayer.clearMediaItems() }
-            // Disable auto-enter when leaving the player so the rest of the
+            val intent = Intent(context, PlaybackService::class.java).apply {
-            // app doesn't accidentally PiP on background.
+                component = ComponentName(context, PlaybackService::class.java)
-            if (activity != null && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+                putExtra(PlaybackService.EXTRA_URL, audio)
-                val off = PictureInPictureParams.Builder()
+                putExtra(PlaybackService.EXTRA_TITLE, title)
-                    .setAutoEnterEnabled(false)
+                putExtra(PlaybackService.EXTRA_POSITION_MS, position)
-                    .build()
-                runCatching { activity.setPictureInPictureParams(off) }
             }
+            ContextCompat.startForegroundService(context, intent)
         }
+        onDispose { PlayerLeaveHandler.handler = null }
     }
 
     // AUD-MED: pause playback when app goes to background. Without this,
@@ -382,12 +382,14 @@ fun PlayerScreen(
                             Toast.makeText(context, "no audio stream", Toast.LENGTH_SHORT).show()
                             return@OverlayButton
                         }
+                        val position = exoPlayer.currentPosition.coerceAtLeast(0L)
                         runCatching { exoPlayer.stop() }
                         runCatching { exoPlayer.clearMediaItems() }
                         val intent = Intent(context, PlaybackService::class.java).apply {
                             component = ComponentName(context, PlaybackService::class.java)
                             putExtra(PlaybackService.EXTRA_URL, audio)
                             putExtra(PlaybackService.EXTRA_TITLE, title)
+                            putExtra(PlaybackService.EXTRA_POSITION_MS, position)
                         }
                         ContextCompat.startForegroundService(context, intent)
                         Toast.makeText(