fix(download): detect mislabeled MP4 before native metadata writes

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

@@ -0,0 +1,58 @@
+package com.zarz.spotiflac
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import java.io.File
+import org.json.JSONObject
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+class NativeDownloadContainerTest {
+    @Test
+    fun misnamedMp4IsTaggedAndPublishedAsM4aWithoutOverwritingExistingAudio() {
+        val context = InstrumentationRegistry.getInstrumentation().targetContext
+        val root = File(context.cacheDir, "container-test-${System.nanoTime()}").apply { mkdirs() }
+        try {
+            val input = File(root, "track.flac")
+            val existing = File(root, "track.m4a").apply { writeText("existing download") }
+            val fixture = NativeDownloadFinalizer.runFFmpegArguments(arrayOf(
+                "-v", "error", "-f", "lavfi", "-i", "sine=frequency=997:sample_rate=44100",
+                "-t", "0.2", "-c:a", "aac", "-f", "mp4", input.path,
+            ))
+            assertTrue(fixture.second, fixture.first)
+            assertTrue(isMP4ContainerFile(input.path))
+            val request = JSONObject()
+                .put("contract_version", 1).put("item_id", "example-track")
+                .put("service", "example-provider").put("track_name", "Container test")
+                .put("artist_name", "Example artist").put("album_name", "Example album")
+                .put("quality", "LOSSLESS").put("storage_mode", "app")
+                .put("output_ext", ".flac").put("embed_metadata", true)
+            val result = NativeDownloadFinalizer.finalize(
+                context, "example-track", request.toString(), "{}",
+                JSONObject().put("success", true).put("file_path", input.path)
+                    .put("file_name", input.name),
+                "{\"save_download_history\":false}",
+            )
+            assertTrue(result.toString(), result.getBoolean("success"))
+            assertTrue(result.getBoolean("native_finalized"))
+            val output = File(result.getString("file_path"))
+            assertEquals("m4a", output.extension)
+            assertTrue(output.length() > 0)
+            assertTrue(isMP4ContainerFile(output.path))
+            assertFalse(input.exists())
+            assertEquals("existing download", existing.readText())
+            val probe = NativeDownloadFinalizer.runFFmpegArguments(arrayOf(
+                "-hide_banner", "-i", output.path, "-map", "0:a:0", "-f", "null", "-",
+            ))
+            assertTrue(probe.second, probe.first)
+            assertTrue(probe.second, probe.second.contains("Container test"))
+            assertTrue(probe.second, probe.second.contains("Audio: aac"))
+        } finally {
+            root.deleteRecursively()
+        }
+    }
+}