Stop a permission answer starting a second conversion (#202)

currentInput() answered for Converting, Waiting and Converted as well as Ready. Those three
arms were unreachable by tapping Convert -- the button renders only in the Ready branch --
but they were reachable through the POST_NOTIFICATIONS *result*, which ConverterScreen.kt:91
wires to convert() rather than to the button.

Reaching one enqueued a SECOND job over a live one: activeWorkId was overwritten, and the
first job kept running with its foreground notification orphaned and nothing left holding
its id to cancel it.

#202 decided to narrow rather than to test it as it stood, because a test written against
the old shape would have frozen the double-enqueue as intended behaviour -- the F1/F5 failure
mode docs/coverage-read-findings.md names. currentInput() is now
(_state.value as? ConversionState.Ready)?.input, which is what JoinViewModel.join() has been
all along; the two screens are the same shape and only one of them was over-general.

Four cold refusal arms come with it, all reached the same way -- a system callback arriving
after the screen has moved on, which is what a result redelivered after process death does:

  ConversionViewModel.kt:513   currentInput() ?: return
  ConversionViewModel.kt:600   pendingSave() ?: return
  JoinViewModel.kt:316         (as? Ready)?.inputs ?: return
  JoinViewModel.kt:390         pendingSave() ?: return

One fixture note worth keeping: the second case needs a real staged file in the worker's
output Data. A SUCCEEDED job with no output path maps to Failed rather than Converted, so
Data.EMPTY never reaches the state the case is about -- which cost a timed-out awaitState
before it was spotted.

Mutations, all run and restored:

  restore the over-general four-arm when   1 red  <- the defect this change fixes
  currentInput()!! at :513                 2 red
  pendingSave()!! in save()                1 red
  drop both join guards                    1 red

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

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

@@ -673,13 +673,23 @@ class ConversionViewModel @JvmOverloads constructor(
         else -> null
     }
 
-    private fun currentInput(): InputFile? = when (val s = _state.value) {
-        is ConversionState.Ready -> s.input
-        is ConversionState.Converting -> s.input
-        is ConversionState.Waiting -> s.input
-        is ConversionState.Converted -> s.input
-        else -> null
-    }
+    /**
+     * The input `convert()` may act on, which is only ever the one on a `Ready` screen.
+     *
+     * This used to answer for `Converting`, `Waiting` and `Converted` as well. Those arms were not
+     * reachable by tapping Convert -- the button renders only in the `Ready` branch -- but they
+     * were reachable through the POST_NOTIFICATIONS **result**, which `ConverterScreen.kt:91` wires
+     * to `convert()` rather than to the button. Reaching one of them enqueued a *second* job over a
+     * live one: `activeWorkId` was overwritten, and the first job kept running with its foreground
+     * notification orphaned and nothing left holding its id to cancel it.
+     *
+     * Narrowed under #202 rather than tested as it stood, because a test written against the old
+     * shape would have frozen the double-enqueue as intended behaviour -- the F1/F5 failure mode.
+     *
+     * `JoinViewModel.join()` has been `(_state.value as? JoinState.Ready)?.inputs ?: return` all
+     * along. The two screens are the same shape and only one of them was over-general.
+     */
+    private fun currentInput(): InputFile? = (_state.value as? ConversionState.Ready)?.input
 
     private companion object {
         /**

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

@@ -51,10 +51,13 @@ import java.io.File
  *   here needs. `OutputPublisherPublishTest` owns what a real publish writes.
  * - **The screen's two buttons.** `ConverterStateAffordancesTest` and `JoinStateAffordancesTest`
  *   own what each state renders; this file owns what each state carries.
- * - **`ConverterScreen`'s `destinationMime` line itself.** It lives in the entry point, above the
- *   `ScreenContent` seam, and reaching it needs a real ViewModel inside a composition. What it
- *   reads -- `pendingSave()?.mimeType` -- is asserted directly instead, which is why that
- *   derivation was moved out of the entry point in the first place.
+ * - ~~**`ConverterScreen`'s `destinationMime` line itself.**~~ **Withdrawn 2026-09-02 (#201).** The
+ *   exemption read: "it lives in the entry point, above the `ScreenContent` seam, and reaching it
+ *   needs a real ViewModel inside a composition". That was true when written and is no longer:
+ *   `AdaptiveShellTest` (#173) established composing the real screens with real ViewModels, and
+ *   #200 added the `ShadowActivity` mechanics for reading what a launcher launched. `RetrySaveMimeTest`
+ *   now asserts the line directly. What this file still owns is the half below the seam -- what each
+ *   state *carries* -- which is why `pendingSave()?.mimeType` is also asserted here.
  * - **Picking a new input while a `Failed` carries a file.** `onInputPicked` overwrites the state
  *   without discarding, from `Converted` exactly as much as from a carrying `Failed`, and neither
  *   branch renders a picker. It is a pre-existing path this change neither opens nor widens: the

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

@@ -0,0 +1,141 @@
+package org.libremediaconverter.convert
+
+import android.app.Activity
+import android.content.Intent
+import android.net.Uri
+import androidx.activity.ComponentActivity
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.performClick
+import androidx.media3.common.util.UnstableApi
+import androidx.work.Data
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremediaconverter.join.JoinScreen
+import org.libremediaconverter.model.InputProbe
+import org.libremediaconverter.ui.TestTags
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+import org.robolectric.Shadows.shadowOf
+import org.robolectric.shadows.ShadowActivity
+
+/**
+ * The launcher layer above the `ScreenContent` seam — registered, and until now never resulted.
+ *
+ * ## The hazard this exists for
+ *
+ * `ConversionViewModel.onInputPicked(uri: Uri)` and `.save(destination: Uri)` are **both
+ * `(Uri) -> Unit`**, so swapping the two launcher callbacks at `ConverterScreen.kt:70` and `:83`
+ * compiles, renders, and passes the entire suite. Picking a file would attempt a save to it, and
+ * choosing a destination would load it as input.
+ *
+ * That is precisely the defect class `ScreenWiringTest` exists for, on the one pair it declines to
+ * cover: it drives `converterActions` directly and says the launcher-backed actions stay
+ * parameters. Correct for the `actions` seam, and it leaves the edge above that seam unpinned.
+ *
+ * Join's equivalents (`JoinScreen.kt:45`, `:55`) are `List<Uri>` and `Uri`, so they are **not**
+ * transposable and need no such test. The picker filter is a different matter and is covered below
+ * for both screens.
+ *
+ * ## The two mechanics, verified before the assertions were written
+ *
+ * Neither is used anywhere else in the suite, so both were spiked first:
+ *
+ * - **Reading what was launched** — `shadowOf(activity).nextStartedActivityForResult`, which returns
+ *   the `Intent` with its `EXTRA_MIME_TYPES` intact.
+ * - **Delivering a result** — `shadowOf(activity).receiveResult(...)`, which reaches
+ *   `ComponentActivity`'s `ActivityResultRegistry` and fires the `rememberLauncherForActivityResult`
+ *   callback.
+ *
+ * `createAndroidComposeRule`, as `AdaptiveShellTest` uses and for the reason it gives: the screens
+ * compose real ViewModels through `viewModel()`, and the plain rule supplies no `ViewModelStoreOwner`.
+ */
+@UnstableApi
+@RunWith(RobolectricTestRunner::class)
+class LauncherWiringTest {
+
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    @Before
+    fun setUp() {
+        val app = RuntimeEnvironment.getApplication()
+        installTestWorkManager(app, Data.EMPTY)
+        // The real screen composes a real ViewModel; neither test here is about probing.
+        ConversionDependencies.probe = { _, _ -> InputProbe() }
+    }
+
+    @After
+    fun tearDown() = ConversionDependencies.reset()
+
+    /**
+     * The transposition guard. A picked file has to reach `onInputPicked`, which is observable as
+     * the screen arriving at `Ready` with the file card showing — `save()` from `Idle` returns at
+     * its own guard and leaves nothing behind.
+     */
+    @Test
+    fun `a picked document is loaded as input rather than saved to`() {
+        composeRule.setContent { ConverterScreen() }
+
+        composeRule.onNodeWithTag(TestTags.Converter.CHOOSE_FILE).performClick()
+        deliver(Uri.parse("content://test/holiday.mkv"))
+
+        composeRule.onNodeWithTag(TestTags.Converter.FILE_CARD_NAME).assertIsDisplayed()
+    }
+
+    /**
+     * `ConverterScreen.kt:65-67` records why the all-types wildcard is load-bearing rather than lazy:
+     *
+     * > the picker is images and video only, offers no audio at all, and will not reliably surface
+     * > .mkv/.flac/.webm
+     *
+     * Narrowing it would make every audio conversion unreachable from the file picker, and nothing
+     * would have gone red. (The literal is spelled only in the assertion below: a KDoc cannot
+     * contain it, because the wildcard's second half closes the comment.)
+     */
+    @Test
+    fun `the converter picker asks for every type, not just the ones a photo picker offers`() {
+        composeRule.setContent { ConverterScreen() }
+
+        composeRule.onNodeWithTag(TestTags.Converter.CHOOSE_FILE).performClick()
+
+        val intent = launched().intent
+        assertEquals(Intent.ACTION_OPEN_DOCUMENT, intent.action)
+        assertEquals(listOf("*/*"), intent.getStringArrayExtra(Intent.EXTRA_MIME_TYPES)?.toList())
+    }
+
+    @Test
+    fun `the join picker asks for video and accepts more than one file`() {
+        composeRule.setContent { JoinScreen() }
+
+        composeRule.onNodeWithTag(TestTags.Join.CHOOSE_FILES).performClick()
+
+        val intent = launched().intent
+        assertEquals(Intent.ACTION_OPEN_DOCUMENT, intent.action)
+        assertEquals(listOf("video/*"), intent.getStringArrayExtra(Intent.EXTRA_MIME_TYPES)?.toList())
+        // A join of one file is not a join; the contract is what asks for several.
+        assertEquals(true, intent.getBooleanExtra(Intent.EXTRA_ALLOW_MULTIPLE, false))
+    }
+
+    private fun launched(): ShadowActivity.IntentForResult {
+        composeRule.waitForIdle()
+        return requireNotNull(shadowOf(composeRule.activity).nextStartedActivityForResult) {
+            "nothing was launched for a result"
+        }
+    }
+
+    private fun deliver(uri: Uri) {
+        val started = launched()
+        shadowOf(composeRule.activity).receiveResult(
+            started.intent,
+            Activity.RESULT_OK,
+            Intent().setData(uri),
+        )
+        composeRule.waitForIdle()
+    }
+}

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

@@ -0,0 +1,136 @@
+package org.libremediaconverter.convert
+
+import android.app.Application
+import android.content.Intent
+import android.net.Uri
+import androidx.activity.ComponentActivity
+import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
+import androidx.compose.ui.test.onNodeWithTag
+import androidx.compose.ui.test.performClick
+import androidx.compose.ui.test.performScrollTo
+import androidx.media3.common.util.UnstableApi
+import androidx.work.WorkManager
+import androidx.work.workDataOf
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremediaconverter.model.InputProbe
+import org.libremediaconverter.model.OutputFormat
+import org.libremediaconverter.ui.TestTags
+import org.libremediaconverter.work.ConversionWorker
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+import org.robolectric.Shadows.shadowOf
+import java.io.File
+
+/**
+ * The save dialog opens with the type the *job* produced, not the type the picker is showing now.
+ *
+ * `ConverterScreen.kt:80` — `state.pendingSave()?.mimeType ?: settings.spec.mimeType` — had never
+ * taken its left-hand side. Its comment records what the line is for:
+ *
+ * > a retry offered after a failed save opens the dialog with the type its first attempt used —
+ * > the cast answered null for a `Failed`, and the fallback below is the current picker, which a
+ * > reattached job never set.
+ *
+ * So the untested half is the fix, and the tested half is the fallback it was added to stop being
+ * used.
+ *
+ * ## This revises a named exemption, deliberately
+ *
+ * `FailedSaveRetryTest`'s KDoc lists this line under "Not asserted here, so each is a decision
+ * rather than an omission":
+ *
+ * > It lives in the entry point, above the `ScreenContent` seam, and reaching it needs a real
+ * > ViewModel inside a composition.
+ *
+ * That was true when written. `AdaptiveShellTest` (#173) then established exactly that capability,
+ * and #200 added the two `ShadowActivity` mechanics that let a test read what a launcher launched.
+ * The reason the exemption gave no longer holds, so the exemption is withdrawn rather than left to
+ * be taken at face value — the same shape as #141 revising #84's boundary. That KDoc is corrected
+ * in this change.
+ *
+ * ## Why the job is reattached rather than run
+ *
+ * The screen composes its own ViewModel through `viewModel()`, so nothing can be injected into it.
+ * A job finished before the composition is the one route to a `Converted` state carrying output
+ * `Data` this test chose — and it is also the case the line exists for, since a reattached job's
+ * spec "was never in these settings at all".
+ */
+@UnstableApi
+@RunWith(RobolectricTestRunner::class)
+class RetrySaveMimeTest {
+
+    @get:Rule
+    val composeRule = createAndroidComposeRule<ComponentActivity>()
+
+    private lateinit var app: Application
+    private lateinit var staged: File
+
+    @Before
+    fun setUp() {
+        app = RuntimeEnvironment.getApplication()
+        ConversionDependencies.probe = { _, _ -> InputProbe() }
+        staged = OutputPublisher(app).createStagingFile("holiday.mkv").apply { writeBytes(ByteArray(4096)) }
+    }
+
+    @After
+    fun tearDown() = ConversionDependencies.reset()
+
+    @Test
+    fun `the save dialog offers the type the job produced, not the one the picker is showing`() {
+        finishAJobProducing(JOB_MIME_TYPE)
+        composeRule.setContent { ConverterScreen() }
+        composeRule.waitForIdle()
+
+        composeRule.onNodeWithTag(TestTags.SAVE_FILE).performScrollTo().performClick()
+        composeRule.waitForIdle()
+
+        val intent = requireNotNull(shadowOf(composeRule.activity).nextStartedActivityForResult) {
+            "the save dialog was never launched"
+        }.intent
+        assertEquals(Intent.ACTION_CREATE_DOCUMENT, intent.action)
+        assertEquals(JOB_MIME_TYPE, intent.type)
+        // The fixture is only meaningful while the two differ; without this the assertion above
+        // would pass just as well against the fallback.
+        assertNotEquals(
+            "the picker's own type must differ, or this test proves nothing",
+            JOB_MIME_TYPE,
+            OutputFormat.MP4_H265.spec.mimeType,
+        )
+    }
+
+    /**
+     * A conversion that finished while nothing was watching, which is what `reattach()` picks up.
+     *
+     * `SucceedingWorkerFactory` reports this output `Data` for whatever is enqueued, so the job
+     * lands `SUCCEEDED` carrying a staged path that exists — the two things `Reattachment.choose`
+     * requires of a finished job.
+     */
+    private fun finishAJobProducing(mimeType: String) {
+        installTestWorkManager(
+            app,
+            workDataOf(
+                ConversionWorker.KEY_OUTPUT_PATH to staged.absolutePath,
+                ConversionWorker.KEY_SUGGESTED_NAME to "holiday.mkv",
+                ConversionWorker.KEY_MIME_TYPE to mimeType,
+            ),
+        )
+        WorkManager.getInstance(app).enqueue(
+            ConversionWorker.request(
+                inputUri = Uri.parse("content://test/holiday.mkv"),
+                displayName = "holiday.mkv",
+                sizeBytes = 4_096L,
+            ),
+        ).result.get()
+    }
+
+    private companion object {
+        /** Matroska, against the MP4 the picker defaults to. */
+        const val JOB_MIME_TYPE = "video/x-matroska"
+    }
+}

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

@@ -0,0 +1,147 @@
+package org.libremediaconverter.convert
+
+import android.app.Application
+import android.net.Uri
+import androidx.media3.common.util.UnstableApi
+import androidx.work.WorkManager
+import androidx.work.workDataOf
+import kotlinx.coroutines.Dispatchers
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremediaconverter.join.JoinState
+import org.libremediaconverter.join.JoinViewModel
+import org.libremediaconverter.model.InputProbe
+import org.libremediaconverter.work.ConcatWorker
+import org.libremediaconverter.work.ConversionWorker
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+
+/**
+ * An answer that arrives after the screen has moved on does nothing.
+ *
+ * Four refusal arms, cold before this file:
+ *
+ * ```
+ * convert/ConversionViewModel.kt:513   currentInput() ?: return
+ * convert/ConversionViewModel.kt:600   pendingSave() ?: return
+ * join/JoinViewModel.kt:316            (as? Ready)?.inputs ?: return
+ * join/JoinViewModel.kt:390            pendingSave() ?: return
+ * ```
+ *
+ * They are not merely defensive. `ConverterScreen.kt:91` wires `convert()` to the
+ * **POST_NOTIFICATIONS result**, and `:83` wires `save()` to the CreateDocument result — so both
+ * are entered by a system callback rather than by a tap, and a result redelivered after process
+ * death arrives at a brand-new ViewModel sitting on `Idle`.
+ *
+ * ## The production change that came with this
+ *
+ * `currentInput()` used to answer for `Converting`, `Waiting` and `Converted` as well as `Ready`.
+ * Those arms were unreachable by tapping Convert but reachable through that permission callback,
+ * and reaching one enqueued a **second** job over a live one — `activeWorkId` overwritten, the
+ * first job still running with an orphaned notification and nothing holding its id.
+ *
+ * #202 decided to narrow rather than to test it as it stood, because a test written against the old
+ * shape would have frozen the double-enqueue as intended behaviour. `JoinViewModel.join()` has been
+ * `(_state.value as? JoinState.Ready)?.inputs ?: return` all along; the two screens are the same
+ * shape and only one was over-general.
+ */
+@UnstableApi
+@RunWith(RobolectricTestRunner::class)
+class StaleLauncherResultTest {
+
+    private lateinit var app: Application
+    private lateinit var workManager: WorkManager
+    private lateinit var staged: java.io.File
+
+    @Before
+    fun setUp() {
+        app = RuntimeEnvironment.getApplication()
+        val publisher = RecordingPublisher(app)
+        ConversionDependencies.publisher = { publisher }
+        ConversionDependencies.probe = { _, _ -> InputProbe() }
+        // A real staged file, because a SUCCEEDED job with no output path maps to Failed rather
+        // than Converted -- and Converted is the state this file's second case has to reach.
+        staged = publisher.createStagingFile("holiday.mp4").apply { writeBytes(ByteArray(4096)) }
+        installTestWorkManager(
+            app,
+            workDataOf(
+                ConversionWorker.KEY_OUTPUT_PATH to staged.absolutePath,
+                ConversionWorker.KEY_SUGGESTED_NAME to "holiday.mp4",
+                ConversionWorker.KEY_MIME_TYPE to "video/mp4",
+            ),
+        )
+        workManager = WorkManager.getInstance(app)
+    }
+
+    @After
+    fun tearDown() = ConversionDependencies.reset()
+
+    @Test
+    fun `a permission answer arriving on an empty screen enqueues nothing`() {
+        val viewModel = ConversionViewModel(app, Dispatchers.Unconfined)
+        awaitState(viewModel.state, "Idle") { it is ConversionState.Idle }
+
+        viewModel.convert()
+
+        assertEquals(ConversionState.Idle, viewModel.state.value)
+        assertEquals("nothing may be enqueued for a file that is not there", 0, conversionJobs())
+    }
+
+    /**
+     * The narrowing itself: a permission answer that arrives while a conversion is already running
+     * must not start a second one.
+     *
+     * Reached by converting once — the synchronous test WorkManager finishes it inline, so the
+     * screen is `Converted`, which is one of the three arms `currentInput()` used to answer for.
+     * Calling `convert()` again from there is precisely what the permission callback can do.
+     */
+    @Test
+    fun `a permission answer arriving after the job finished does not start a second one`() {
+        val viewModel = ConversionViewModel(app, Dispatchers.Unconfined)
+        viewModel.onInputPicked(Uri.parse("content://test/holiday.mkv"))
+        awaitState(viewModel.state, "Ready") { it is ConversionState.Ready }
+        viewModel.convert()
+        val converted = awaitState(viewModel.state, "Converted") { it is ConversionState.Converted }
+        assertEquals("the fixture needs exactly one job to start with", 1, conversionJobs())
+
+        viewModel.convert()
+
+        assertEquals("a second job must not be enqueued over the first", 1, conversionJobs())
+        assertEquals("and the screen must not move", converted, viewModel.state.value)
+    }
+
+    @Test
+    fun `a save answer arriving on an empty screen does nothing`() {
+        val viewModel = ConversionViewModel(app, Dispatchers.Unconfined)
+        awaitState(viewModel.state, "Idle") { it is ConversionState.Idle }
+
+        viewModel.save(DESTINATION)
+
+        assertEquals(ConversionState.Idle, viewModel.state.value)
+    }
+
+    @Test
+    fun `a join answer arriving on an empty screen enqueues nothing`() {
+        val viewModel = JoinViewModel(app, Dispatchers.Unconfined)
+        awaitState(viewModel.state, "Idle") { it is JoinState.Idle }
+
+        viewModel.join()
+        viewModel.save(DESTINATION)
+
+        assertEquals(JoinState.Idle, viewModel.state.value)
+        assertEquals(0, joinJobs())
+    }
+
+    private fun conversionJobs() = jobsTagged(ConversionWorker::class.java.name)
+
+    private fun joinJobs() = jobsTagged(ConcatWorker::class.java.name)
+
+    private fun jobsTagged(tag: String) = workManager.getWorkInfosByTag(tag).get().size
+
+    private companion object {
+        val DESTINATION: Uri = Uri.parse("content://test/destination.mp4")
+    }
+}

app/src/test/java/org/libremediaconverter/ui/theme/ThemeFollowsSystemTest.kt

@@ -0,0 +1,89 @@
+package org.libremediaconverter.ui.theme
+
+import androidx.compose.material3.ColorScheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.ui.test.junit4.v2.createComposeRule
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * The theme called the way the app calls it: with no arguments at all.
+ *
+ * [ThemeColorSchemeTest] resolves every branch of the `when` and always passes `darkTheme`
+ * explicitly, so the `$default` bridge is never entered and **`isSystemInDarkTheme()` is never
+ * called**. `MainActivity.kt:79` is its only default-argument caller and does not execute on the
+ * JVM, which left the app's actual call shape the one nothing exercised —
+ * `LibreMediaConverterTheme` reported `mi=21, mb=6, cb=12` at method level.
+ *
+ * ## Not #68
+ *
+ * #68 is about the two **unreachable** arms, `DarkColorScheme` and `LightColorScheme`, which cannot
+ * run because `dynamicColor` is always `true` and nothing can flip it. That is an open product
+ * decision. This is the reachable half — whether the default follows the system — and closing it
+ * does not close that.
+ *
+ * ## Why the assertion compares schemes rather than reading a number
+ *
+ * A luminance threshold would be a guess about the device palette. What is asserted instead is that
+ * the no-argument call resolves to **the same scheme** an explicit `darkTheme` of the matching
+ * value does, and a different one from its opposite. That holds whatever palette the platform
+ * hands back, and it is exactly the claim: the default reads the system rather than picking a side.
+ *
+ * Both schemes are resolved in one composition because `setContent` may be called once per test.
+ */
+@RunWith(RobolectricTestRunner::class)
+class ThemeFollowsSystemTest {
+
+    @get:Rule
+    val composeRule = createComposeRule()
+
+    @Test
+    @Config(qualifiers = "+night")
+    fun `with no arguments the theme follows a system in dark mode`() {
+        val resolved = resolve()
+
+        assertEquals("the default must resolve what darkTheme = true does", resolved.dark, resolved.bare)
+        assertNotEquals(resolved.light, resolved.bare)
+    }
+
+    @Test
+    @Config(qualifiers = "+notnight")
+    fun `with no arguments the theme follows a system in light mode`() {
+        val resolved = resolve()
+
+        assertEquals("the default must resolve what darkTheme = false does", resolved.light, resolved.bare)
+        assertNotEquals(resolved.dark, resolved.bare)
+    }
+
+    /**
+     * The three colours are read together as one value, because any single one could coincide
+     * between the two schemes on some palette while the schemes themselves differ. Background is
+     * what dark mode is chiefly about; primary and surface are along to make a coincidence
+     * implausible rather than merely unlikely.
+     */
+    private data class Fingerprint(val background: Long, val primary: Long, val surface: Long)
+
+    private fun ColorScheme.fingerprint() =
+        Fingerprint(background.value.toLong(), primary.value.toLong(), surface.value.toLong())
+
+    private class Resolved(val bare: Fingerprint, val dark: Fingerprint, val light: Fingerprint)
+
+    private fun resolve(): Resolved {
+        lateinit var bare: Fingerprint
+        lateinit var dark: Fingerprint
+        lateinit var light: Fingerprint
+        composeRule.setContent {
+            // No arguments — the call MainActivity makes, and the one nothing exercised.
+            LibreMediaConverterTheme { bare = MaterialTheme.colorScheme.fingerprint() }
+            LibreMediaConverterTheme(darkTheme = true) { dark = MaterialTheme.colorScheme.fingerprint() }
+            LibreMediaConverterTheme(darkTheme = false) { light = MaterialTheme.colorScheme.fingerprint() }
+        }
+        composeRule.waitForIdle()
+        return Resolved(bare, dark, light)
+    }
+}

app/src/test/java/org/libremediaconverter/work/ProgressNotificationTest.kt

@@ -21,8 +21,10 @@ import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.libremediaconverter.convert.ConversionDependencies
+import org.libremediaconverter.convert.HardwareTranscoder
 import org.libremediaconverter.convert.SoftwareTranscoder
 import org.libremediaconverter.convert.installTestWorkManager
+import org.libremediaconverter.model.Container
 import org.libremediaconverter.model.ConversionRequest
 import org.libremediaconverter.model.DeviceCodecs
 import org.libremediaconverter.model.EnginePreference
@@ -129,6 +131,40 @@ class ProgressNotificationTest {
         )
     }
 
+    /**
+     * The same plumbing on the engine most conversions actually use, which had none.
+     *
+     * `ConversionWorker.kt:208-210` is a second `onProgress` lambda at a second call site — the one
+     * handed to `engine.transcode` — and it reported `ci == 0`. Every test above drives the FFmpeg
+     * path; `HardwareFallbackTest` reaches `runMedia3OrFallBack` but its recording transcoder
+     * records the call and never invokes the callback it was given. So the two engines' progress
+     * wiring was one tested and one not, and the untested one is the default: `ConversionRouter`
+     * sends everything it can to Media3.
+     *
+     * `AUTO` with a real H.264 probe, because `FORCE_SOFTWARE` is precisely what keeps the other
+     * tests out of this branch. The probe and the permissive codec profile are what let the router
+     * choose Media3 at all — `InputProbe()` reports `UNPARSEABLE`, which routes straight to FFmpeg.
+     *
+     * Asserted on the *percentage*, not merely on an update having happened: `publishProgress`
+     * takes a display name and a percent, and replacing the percent with a constant compiles.
+     */
+    @Test
+    fun `progress from the hardware engine reaches WorkManager the same way FFmpeg's does`() {
+        ConversionDependencies.probe = { _, _ -> H264_SOURCE }
+        val reporting = ReportingHardwareTranscoder { onProgress -> onProgress(PERCENT) }
+        ConversionDependencies.hardware = { reporting }
+
+        runBlocking { workerReporting(EnginePreference.AUTO) { }.doWork() }
+
+        assertEquals("the job must have gone to the hardware engine", 1, reporting.attempts)
+        val progressUpdates = updater.infos.drop(1)
+        assertEquals("one throttled progress update expected", 1, progressUpdates.size)
+        assertEquals(
+            PERCENT,
+            progressUpdates.single().notification.extras.getInt(Notification.EXTRA_PROGRESS),
+        )
+    }
+
     /**
      * A worker routed to the software engine, whose engine is [report] and a written output.
      *
@@ -137,7 +173,10 @@ class ProgressNotificationTest {
      * bridge, which is native. [report] is handed the worker's own progress callback, and runs with
      * the worker as its receiver so a test can stop it mid-transcode.
      */
-    private fun workerReporting(report: ConversionWorker.((Int) -> Unit) -> Unit): ConversionWorker {
+    private fun workerReporting(
+        enginePreference: EnginePreference = EnginePreference.FORCE_SOFTWARE,
+        report: ConversionWorker.((Int) -> Unit) -> Unit,
+    ): ConversionWorker {
         val worker = TestListenableWorkerBuilder<ConversionWorker>(
             context = app,
             inputData = workDataOf(
@@ -147,7 +186,7 @@ class ProgressNotificationTest {
                 ConversionWorker.KEY_CONTAINER to SPEC.container.name,
                 ConversionWorker.KEY_VIDEO_CODEC to SPEC.videoCodec.name,
                 ConversionWorker.KEY_AUDIO_CODEC to SPEC.audioCodec.name,
-                ConversionWorker.KEY_ENGINE_PREFERENCE to EnginePreference.FORCE_SOFTWARE.name,
+                ConversionWorker.KEY_ENGINE_PREFERENCE to enginePreference.name,
             ),
             runAttemptCount = 0,
         ).setId(JOB_ID)
@@ -171,6 +210,17 @@ class ProgressNotificationTest {
         const val TICKS = 50
         val SPEC = OutputFormat.MP4_H265.spec
         val JOB_ID: UUID = UUID.fromString("00000000-0000-4000-8000-000000000021")
+
+        /**
+         * A probe the router can actually route. `InputProbe()` reports `UNPARSEABLE`, which
+         * `PERMISSIVE.canDecode` refuses, so every job would reach FFmpeg with no test saying why.
+         */
+        val H264_SOURCE = InputProbe(
+            videoCodec = "h264",
+            audioCodec = "aac",
+            container = Container.MP4,
+            durationMs = 1_000,
+        )
     }
 }
 
@@ -211,3 +261,22 @@ private class ReportingTranscoder(private val report: ((Int) -> Unit) -> Unit) :
         const val OUTPUT_BYTES = 512
     }
 }
+
+/** A hardware engine that reports whatever [report] wants reported, then writes an output. */
+@UnstableApi
+private class ReportingHardwareTranscoder(private val report: ((Int) -> Unit) -> Unit) : HardwareTranscoder {
+
+    var attempts = 0
+
+    override suspend fun transcode(input: Uri, output: File, request: ConversionRequest, onProgress: (Int) -> Unit) {
+        attempts++
+        report(onProgress)
+        output.writeBytes(ByteArray(OUTPUT_BYTES))
+    }
+
+    override fun close() = Unit
+
+    private companion object {
+        const val OUTPUT_BYTES = 16
+    }
+}