feat(player): add direct USB audio and DSD transport

android/app/src/androidTest/kotlin/com/zarz/spotiflac/UsbBitPerfectPluginTest.kt

@@ -2,6 +2,11 @@ package com.zarz.spotiflac
 
 import android.media.AudioDeviceInfo
 import android.media.AudioManager
+import android.os.ParcelFileDescriptor
+import com.spotiflac.backend.UsbDirectOutput
+import java.io.File
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
 import io.flutter.embedding.engine.FlutterEngine
@@ -12,12 +17,66 @@ import java.util.concurrent.TimeUnit
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
+import org.junit.Assert.assertThrows
 import org.junit.Assume.assumeTrue
 import org.junit.Test
 import org.junit.runner.RunWith
 
 @RunWith(AndroidJUnit4::class)
 class UsbBitPerfectPluginTest {
+    @Test
+    fun directNativeBridgeRejectsNonUsbFdWithoutClosingItsOwner() {
+        val context = InstrumentationRegistry.getInstrumentation().targetContext
+        val file = File.createTempFile("usb-bridge-", ".bin", context.cacheDir)
+        try {
+            file.writeBytes(ByteArray(64))
+            ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY).use { fd ->
+                val descriptors = byteArrayOf(
+                    9, 4, 0, 0, 0, 1, 1, 0, 0,
+                    9, 4, 1, 1, 1, 1, 2, 0, 0,
+                    7, 0x24, 1, 1, 1, 1, 0,
+                    11, 0x24, 2, 1, 2, 2, 16, 1, 0x80.toByte(), 0xbb.toByte(), 0,
+                    9, 5, 1, 0x0d, 0xc0.toByte(), 0, 1, 0, 0,
+                )
+                assertThrows(Exception::class.java) {
+                    UsbDirectOutput.open(fd.fd, descriptors, 48000u, 2u, 16u, false, false)
+                }
+                assertEquals(64L, fd.statSize)
+            }
+        } finally { file.delete() }
+    }
+
+    @Test
+    fun pcmSourceRetainsSafDescriptorAndSeeksWithoutChangingSamples() {
+        val context = InstrumentationRegistry.getInstrumentation().targetContext
+        val file = File.createTempFile("usb-pcm-", ".wav", context.cacheDir)
+        val audioSize = 4800 * 4
+        val wav = ByteBuffer.allocate(44 + audioSize).order(ByteOrder.LITTLE_ENDIAN)
+        wav.put("RIFF".toByteArray()).putInt(36 + audioSize).put("WAVEfmt ".toByteArray())
+            .putInt(16).putShort(1).putShort(2).putInt(48000).putInt(192000).putShort(4).putShort(16)
+            .put("data".toByteArray()).putInt(audioSize)
+        repeat(4800) { wav.putShort(1234).putShort(-1234) }
+        try {
+            file.writeBytes(wav.array())
+            val source = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY).use { fd ->
+                UsbPcmSource("/proc/self/fd/${fd.fd}")
+            }
+            source.use {
+                assertEquals(48000, it.rate)
+                assertEquals(16, it.bits)
+                for (target in listOf(0L, 50000L)) {
+                    it.seek(target)
+                    val decoded = requireNotNull(it.read(32)).order(ByteOrder.LITTLE_ENDIAN)
+                    assertTrue(decoded.remaining() > 0)
+                    while (decoded.hasRemaining()) {
+                        assertEquals(1234 shl 16, decoded.int)
+                        assertEquals(-1234 shl 16, decoded.int)
+                    }
+                }
+            }
+        } finally { file.delete() }
+    }
+
     @Test
     fun unsupportedRouteReturnsFallbackAndEngineDetachesCleanly() {
         val instrumentation = InstrumentationRegistry.getInstrumentation()
@@ -56,6 +115,10 @@ class UsbBitPerfectPluginTest {
             assertEquals(if (android.os.Build.VERSION.SDK_INT >= 34) "no_usb" else "android_version", result["reason"])
             assertNull(result["ready"])
             invoke("stop")
+            val direct = invoke("prepare", mapOf("path" to "/unopened.dsf", "token" to 2, "direct" to true)) as Map<*, *>
+            assertEquals("no_usb", direct["reason"])
+            assertNull(direct["ready"])
+            invoke("stop")
         } finally {
             instrumentation.runOnMainSync { engine.destroy() }
         }