C2 (#177): cut MediaProbe's two-probe merge into a seam, and ask which probe wins

probe() runs MediaExtractor and FFprobe independently and merges the two, and every rule
in that merge is a decision nothing held. The reason is structural rather than an
oversight: RemuxTest drives the whole thing on a device against committed fixtures, but
only ever with one probe answering and the other agreeing or also failing. Nothing on any
source set can arrange for a real extractor and a real FFprobe to *disagree*, so every
elvis in the merge was taken in one direction and never the other.

The seam is `internal fun merge(Extracted?, FFprobeInfo?): InputProbe`, pulled out of
probe() whole -- probe() now reads the two probes, merges, and keeps the log. FFprobeInfo
becomes internal alongside it; Extracted already was, with a KDoc giving this exact reason,
and FFprobeInfo simply never got the same treatment. Half a signature being private is
what made the function unnameable from a test.

Eleven tests, and the mutations that hold them:

  image beats a real video codec      demote the isImage arm below the video arm
  the extractor wins on codecs        flip the elvis to FFprobe-first
  duration is the larger reading      replace maxOf with extractor-first
  dimensions prefer the extractor     flip the width elvis
  no recognised stream is unreadable  narrow the guard to `extracted == null && info == null`

All five red, then restored. One mutation I tried first was *semantically equivalent* --
moving the image arm above the both-null arm changes nothing for any reachable input -- so
it stayed green and is recorded here rather than counted: a green mutation is only evidence
when the mutation is a real change.

The last row is the arm the ticket was filed for: parsed, and carrying no stream either
probe recognised, which is what a container holding only subtitles looks like. Its input
was already being constructed elsewhere in the suite -- MediaProbeTrackWalkTest calls
extractedFrom(emptyList()) and gets exactly it -- and had never been handed to the merge.

568 -> 579 JVM tests, 0 failures.
MediaProbe: 35 -> 24 missed lines, 72 -> 40 missed branches.
Line 2103/2348 -> 2173/2348; branch 1029/1340 -> 1091/1342.

The branch denominator moved by two, and it is the seam that moved it -- worth stating
separately from the numerator, because CLAUDE.md's coverage entry has a documented history
of explaining its own numbers wrongly.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/main/java/org/libremediaconverter/MainActivity.kt

@@ -24,9 +24,11 @@ import androidx.compose.runtime.saveable.Saver
 import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.testTag
 import androidx.media3.common.util.UnstableApi
 import org.libremediaconverter.convert.ConverterScreen
 import org.libremediaconverter.join.JoinScreen
+import org.libremediaconverter.ui.TestTags
 import org.libremediaconverter.ui.theme.LibreMediaConverterTheme
 
 /**
@@ -114,7 +116,7 @@ internal fun AppRoot(
 
     if (useRail) {
         Row(modifier = Modifier.fillMaxSize()) {
-            NavigationRail {
+            NavigationRail(modifier = Modifier.testTag(TestTags.Shell.NAVIGATION_RAIL)) {
                 Destination.entries.forEach { item ->
                     NavigationRailItem(
                         selected = destination == item,
@@ -132,7 +134,7 @@ internal fun AppRoot(
         Scaffold(
             modifier = Modifier.fillMaxSize(),
             bottomBar = {
-                NavigationBar {
+                NavigationBar(modifier = Modifier.testTag(TestTags.Shell.NAVIGATION_BAR)) {
                     Destination.entries.forEach { item ->
                         NavigationBarItem(
                             selected = destination == item,

app/src/main/java/org/libremediaconverter/convert/MediaProbe.kt

@@ -50,19 +50,42 @@ object MediaProbe {
     )
 
     fun probe(context: Context, uri: Uri): InputProbe {
-        val extracted = probeWithExtractor(context, uri)
-        val info = probeWithFFprobe(context, uri)
+        val merged = merge(probeWithExtractor(context, uri), probeWithFFprobe(context, uri))
+        if (merged.kind == InputKind.UNPARSEABLE) {
+            // Not a failure: an unparseable input is a strong signal that this job belongs on
+            // FFmpeg. Reporting an unknown codec makes the router say so.
+            Log.i(TAG, "Neither MediaExtractor nor FFprobe could read $uri; routing to FFmpeg.")
+        }
+        return merged
+    }
 
+    /**
+     * What the two probes together say about one input.
+     *
+     * A pure function, and `internal` for the same reason [extractedFrom] is: the precedence rules
+     * below are the answer to "which probe wins", and until this was pulled out of [probe] the only
+     * way to ask was to have a real `MediaExtractor` and a real FFprobe **disagree**, which nothing
+     * on any source set can arrange. `RemuxTest` drives this on a device against committed
+     * fixtures, but only ever with one probe answering and the other agreeing or also failing --
+     * so every elvis here was taken in one direction and never the other.
+     *
+     * The rules, each of which is a decision rather than an accident:
+     *
+     * - **The extractor wins on codecs.** It is the platform's own view of what it can decode,
+     *   which is the thing the router is about to ask about. FFprobe's name for the same track can
+     *   differ, and the copy planner keys off these strings.
+     * - **FFprobe alone reports the container.** `MediaExtractor` cannot, which is why [InputProbe]
+     *   carries a nullable one and `CopyPlanner` treats null as "container unknown".
+     * - **Duration is the larger of the two**, not the first non-zero. Either probe can report zero
+     *   for a file the other times correctly, and a zero duration makes the FFmpeg progress
+     *   percentage undefined.
+     */
+    internal fun merge(extracted: Extracted?, info: FFprobeInfo?): InputProbe {
         val videoCodec = extracted?.videoCodec ?: info?.videoCodec
         val audioCodec = extracted?.audioCodec ?: info?.audioCodec
         val kind = classify(extracted, info)
 
-        if (kind == InputKind.UNPARSEABLE) {
-            // Not a failure: an unparseable input is a strong signal that this job belongs on
-            // FFmpeg. Reporting an unknown codec makes the router say so.
-            Log.i(TAG, "Neither MediaExtractor nor FFprobe could read $uri; routing to FFmpeg.")
-            return UNREADABLE
-        }
+        if (kind == InputKind.UNPARSEABLE) return UNREADABLE
 
         return InputProbe(
             videoCodec = videoCodec,
@@ -83,7 +106,7 @@ object MediaProbe {
      * audio file and a corrupt file indistinguishable. The source-info card cannot describe either
      * honestly until they are separate, and neither can the copy planner.
      */
-    private fun classify(extracted: Extracted?, info: FFprobeInfo?): InputKind = when {
+    internal fun classify(extracted: Extracted?, info: FFprobeInfo?): InputKind = when {
         info?.isImage == true -> InputKind.IMAGE
         extracted == null && info == null -> InputKind.UNPARSEABLE
         (extracted?.videoCodec ?: info?.videoCodec) != null -> InputKind.VIDEO
@@ -162,7 +185,11 @@ object MediaProbe {
         }
     }
 
-    private class FFprobeInfo(
+    /**
+     * `internal` rather than `private` for the same reason [Extracted] is, and it should have been
+     * from the start: [merge] cannot be named from a test while half its signature is private.
+     */
+    internal class FFprobeInfo(
         val container: Container?,
         val videoCodec: String?,
         val audioCodec: String?,

app/src/main/java/org/libremediaconverter/ui/TestTags.kt

@@ -56,6 +56,20 @@ object TestTags {
      */
     const val RETRY_SAVE: String = "action.retrySave"
 
+    /**
+     * The adaptive shell around both screens -- `AppRoot`'s two layouts.
+     *
+     * Named because there is no other way to tell them apart from a test. Both render the same two
+     * destinations with the same labels and the same selection state, so every assertion that could
+     * be written without these tags is satisfied by either layout, and transposing the two bodies
+     * passed the whole suite. Exactly one of the two exists at a time, which is what makes
+     * `assertExists` / `assertDoesNotExist` on this pair a statement about the width class.
+     */
+    object Shell {
+        const val NAVIGATION_RAIL: String = "shell.navigationRail"
+        const val NAVIGATION_BAR: String = "shell.navigationBar"
+    }
+
     /** `ConverterScreen`. */
     object Converter {
         const val CHOOSE_FILE: String = "converter.chooseFile"

app/src/test/java/org/libremediaconverter/AdaptiveShellTest.kt

@@ -0,0 +1,129 @@
+package org.libremediaconverter
+
+import androidx.activity.ComponentActivity
+import androidx.compose.material3.windowsizeclass.WindowWidthSizeClass
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import androidx.media3.common.util.UnstableApi
+import androidx.work.Data
+import org.junit.After
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremediaconverter.convert.ConversionDependencies
+import org.libremediaconverter.convert.installTestWorkManager
+import org.libremediaconverter.model.InputProbe
+import org.libremediaconverter.ui.TestTags
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+
+/**
+ * Which navigation affordance the shell actually renders, and which screen it actually shows.
+ *
+ * Assertion gaps rather than coverage gaps, both of them, and that is why they lasted.
+ * `AppRootRestorationTest` already drives `AppRoot` at `Compact` and `Expanded`, so JaCoCo is green
+ * on `useRail` -- but it asserts only that the *selected tab* survives recreation, through a stub
+ * `content` composable. Nothing anywhere queried for a rail or a bar, and nothing rendered the real
+ * screens. Two consequences, both measured before this file existed:
+ *
+ * - **Transposing the `NavigationRail` and `NavigationBar` bodies passed the entire suite.**
+ * - **Transposing `Content`'s two arms passed it too** -- a tablet showing the phone chrome, or the
+ *   Convert tab opening the Join screen, and 546 tests with nothing to say about either.
+ *
+ * `AppRoot`'s own KDoc is why this matters more than it looks: from targetSdk 37 the app is resized
+ * and rotated whether or not it is ready, so the width class is not a preference, it is whatever
+ * the system hands over.
+ *
+ * ## Two things this needed that the rest of the suite does not
+ *
+ * **`createAndroidComposeRule`, not `createComposeRule`.** Rendering `AppRoot` with its *default*
+ * content reaches `ConverterScreen`'s `viewModel = viewModel()`, which needs a
+ * `ViewModelStoreOwner`; the plain rule supplies none. It works because both ViewModels are
+ * `@JvmOverloads constructor(app: Application, …)`, so `AndroidViewModelFactory` can build them,
+ * and because `app/build.gradle.kts` already puts `ui-test-manifest`'s `ComponentActivity` in the
+ * merged manifest the unit tests build against -- which that file says in terms.
+ *
+ * **Tags on the two bars.** They are in `TestTags`, applied inside `main`, for the reason that
+ * file's KDoc gives: a tag the test hands down proves only that the test set it.
+ */
+@UnstableApi
+@RunWith(RobolectricTestRunner::class)
+class AdaptiveShellTest {
+
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    @Before
+    fun setUp() {
+        val app = RuntimeEnvironment.getApplication()
+        installTestWorkManager(app, Data.EMPTY)
+        // The real screens are composed here, so their ViewModels are real too. Neither test is
+        // about probing or publishing; left alone they would reach the FFprobe loader and this
+        // machine's codec list, and decide things no assertion mentions.
+        ConversionDependencies.probe = { _, _ -> InputProbe() }
+    }
+
+    @After
+    fun tearDown() {
+        ConversionDependencies.reset()
+    }
+
+    @Test
+    fun `a phone gets the bottom bar and a tablet gets the rail`() {
+        setShell(WindowWidthSizeClass.Compact)
+
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_BAR).assertExists()
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_RAIL).assertDoesNotExist()
+    }
+
+    @Test
+    fun `an expanded window gets the rail`() {
+        setShell(WindowWidthSizeClass.Expanded)
+
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_RAIL).assertExists()
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_BAR).assertDoesNotExist()
+    }
+
+    /**
+     * The width class no test had ever passed.
+     *
+     * `useRail` is `!= Compact`, so Medium takes the rail with Expanded. Narrowing it to
+     * `== Expanded` is a one-character change that breaks every tablet and unfolded foldable and
+     * nothing else -- and until this test, nothing in either source set used `Medium` at all.
+     */
+    @Test
+    fun `a medium window is a rail window, not a phone`() {
+        setShell(WindowWidthSizeClass.Medium)
+
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_RAIL).assertExists()
+        composeRule.onNodeWithTag(TestTags.Shell.NAVIGATION_BAR).assertDoesNotExist()
+    }
+
+    /**
+     * The mapping every other test stubs out: which screen each destination actually opens.
+     *
+     * Matched on each screen's own "choose a file" affordance rather than on a title, because those
+     * tags are applied by the screens themselves -- so this fails if the destinations are
+     * transposed, and it fails for the right reason.
+     */
+    @Test
+    fun `Convert opens the converter and Join opens the join screen`() {
+        setShell(WindowWidthSizeClass.Compact)
+
+        composeRule.onNodeWithTag(TestTags.Converter.CHOOSE_FILE).assertExists()
+        composeRule.onNodeWithTag(TestTags.Join.CHOOSE_FILES).assertDoesNotExist()
+
+        composeRule.onNodeWithText(Destination.JOIN.label).performClick()
+
+        composeRule.onNodeWithTag(TestTags.Join.CHOOSE_FILES).assertExists()
+        composeRule.onNodeWithTag(TestTags.Converter.CHOOSE_FILE).assertDoesNotExist()
+    }
+
+    /** [AppRoot] with its real content, which is the half nothing else composes. */
+    private fun setShell(width: WindowWidthSizeClass) {
+        composeRule.setContent { AppRoot(width) }
+    }
+}

app/src/test/java/org/libremediaconverter/convert/MediaProbeMergeTest.kt

@@ -0,0 +1,166 @@
+package org.libremediaconverter.convert
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.libremediaconverter.model.Container
+import org.libremediaconverter.model.InputKind
+import org.libremediaconverter.model.InputProbe
+
+/**
+ * Which of the two probes wins, when they disagree.
+ *
+ * [MediaProbe.probe] runs `MediaExtractor` and FFprobe independently and then merges the two, and
+ * every rule in that merge is a decision. None of them had a test, for a reason that is structural
+ * rather than an oversight: `RemuxTest` drives the whole thing on a device against committed
+ * fixtures, but only ever with **one probe answering and the other agreeing or also failing**.
+ * Nothing on any source set can arrange for a real extractor and a real FFprobe to disagree, so
+ * every elvis in the merge was taken in one direction and never the other.
+ *
+ * Cutting `merge` out of `probe` is what makes the question askable. Both halves of its signature
+ * had to become `internal` for that -- `Extracted` already was, with a KDoc giving this exact
+ * reason; `FFprobeInfo` simply never got the same treatment.
+ */
+class MediaProbeMergeTest {
+
+    /**
+     * The rule with the loudest failure mode, and `isImageFormat`'s own KDoc names it: a false
+     * positive here "makes the source-info card describe a video as an image". So the image verdict
+     * has to beat a real video codec from the extractor, and the ordering that makes it do so is
+     * the first arm of `classify` rather than anything a reader would infer from the fields.
+     */
+    @Test
+    fun `an image verdict from FFprobe beats a video codec from the extractor`() {
+        val merged = MediaProbe.merge(
+            extracted = extracted(video = "h264"),
+            info = info(video = "mjpeg", isImage = true),
+        )
+
+        assertEquals(InputKind.IMAGE, merged.kind)
+    }
+
+    @Test
+    fun `the extractor wins on codecs, because it is the view the router will act on`() {
+        val merged = MediaProbe.merge(
+            extracted = extracted(video = "h264", audio = "aac"),
+            info = info(video = "hevc", audio = "mp3"),
+        )
+
+        assertEquals("h264", merged.videoCodec)
+        assertEquals("aac", merged.audioCodec)
+    }
+
+    @Test
+    fun `FFprobe answers for a file the extractor could not open`() {
+        val merged = MediaProbe.merge(extracted = null, info = info(video = "vp9", audio = "opus"))
+
+        assertEquals("vp9", merged.videoCodec)
+        assertEquals("opus", merged.audioCodec)
+        assertEquals(InputKind.VIDEO, merged.kind)
+    }
+
+    @Test
+    fun `the extractor answers for a file FFprobe could not read`() {
+        val merged = MediaProbe.merge(extracted = extracted(video = "h264", audio = "aac"), info = null)
+
+        assertEquals("h264", merged.videoCodec)
+        assertEquals("aac", merged.audioCodec)
+        assertNull("only FFprobe can name the container, so it stays unknown here", merged.container)
+    }
+
+    /**
+     * The larger of the two, not the first non-zero.
+     *
+     * Either probe can report zero for a file the other times correctly, and a zero duration makes
+     * the FFmpeg progress percentage undefined -- `FFmpegEngine` divides by it. Both orderings are
+     * asserted because "take the extractor's" and "take the larger" agree in one direction and not
+     * the other, and only one of them is the rule.
+     */
+    @Test
+    fun `duration is the longer of the two readings, whichever probe supplied it`() {
+        assertEquals(
+            5_000L,
+            MediaProbe.merge(extracted(duration = 0L), info(duration = 5_000L)).durationMs,
+        )
+        assertEquals(
+            5_000L,
+            MediaProbe.merge(extracted(duration = 5_000L), info(duration = 0L)).durationMs,
+        )
+    }
+
+    @Test
+    fun `dimensions come from the extractor, and from FFprobe only when it has none`() {
+        assertEquals(1920, MediaProbe.merge(extracted(width = 1920), info(width = 640)).width)
+        assertEquals(640, MediaProbe.merge(extracted = null, info = info(width = 640)).width)
+        assertEquals(0, MediaProbe.merge(extracted(width = 0), info(width = 0)).width)
+    }
+
+    @Test
+    fun `the container comes from FFprobe, which is the only probe that can name one`() {
+        val merged = MediaProbe.merge(extracted(video = "h264"), info(container = Container.MKV))
+
+        assertEquals(Container.MKV, merged.container)
+    }
+
+    @Test
+    fun `a file with audio and no video is audio-only, not unparseable`() {
+        val merged = MediaProbe.merge(extracted(video = null, audio = "mp3"), info = null)
+
+        assertEquals(InputKind.AUDIO_ONLY, merged.kind)
+        assertFalse(merged.hasVideo)
+    }
+
+    @Test
+    fun `a file neither probe could open is the one unreadable answer`() {
+        val merged = MediaProbe.merge(extracted = null, info = null)
+
+        assertEquals(MediaProbe.UNREADABLE, merged)
+        assertEquals(InputProbe.UNPARSEABLE, merged.videoCodec)
+    }
+
+    /**
+     * The arm the ticket was filed for: parsed, and carrying no stream either probe recognised.
+     *
+     * Distinct from "neither probe could open it" -- here the extractor opened the file happily and
+     * found nothing convertible, which is what a container holding only subtitles looks like. It
+     * has to reach the same [MediaProbe.UNREADABLE] answer, because the router keys off that and
+     * there is nothing here for Media3 to do either way.
+     *
+     * Its input was already being built elsewhere in the suite -- `MediaProbeTrackWalkTest` calls
+     * `extractedFrom(emptyList())` and gets exactly this -- and had simply never been handed to the
+     * merge.
+     */
+    @Test
+    fun `a file that parsed but carries no recognised stream is unreadable too`() {
+        val merged = MediaProbe.merge(extracted = MediaProbe.extractedFrom(emptyList()), info = null)
+
+        assertEquals(InputKind.UNPARSEABLE, merged.kind)
+        assertEquals(MediaProbe.UNREADABLE, merged)
+    }
+
+    @Test
+    fun `hasVideo follows the codec that survived the merge, not either probe alone`() {
+        assertTrue(MediaProbe.merge(extracted(video = null), info(video = "vp9")).hasVideo)
+        assertFalse(MediaProbe.merge(extracted(video = null, audio = "aac"), info(video = null)).hasVideo)
+    }
+
+    private fun extracted(
+        video: String? = "h264",
+        audio: String? = "aac",
+        duration: Long = 1_000L,
+        width: Int = 1280,
+        height: Int = 720,
+    ) = MediaProbe.Extracted(video, audio, duration, width, height)
+
+    private fun info(
+        container: Container? = null,
+        video: String? = "h264",
+        audio: String? = "aac",
+        duration: Long = 1_000L,
+        width: Int = 1280,
+        height: Int = 720,
+        isImage: Boolean = false,
+    ) = MediaProbe.FFprobeInfo(container, video, audio, duration, width, height, isImage)
+}

app/src/test/java/org/libremediaconverter/ui/TagTableUniquenessTest.kt

@@ -28,6 +28,7 @@ class TagTableUniquenessTest {
     fun `every tag constant has its own value`() {
         val tags = tagsIn(
             TestTags::class.java,
+            TestTags.Shell::class.java,
             TestTags.Converter::class.java,
             TestTags.Join::class.java,
         )