Stop the cancel tests losing their race on a loaded runner

Both cancellation tests I added in ad2a75d and d293646 wait for
SessionState.RUNNING and then cancel. That is not enough. The conversion
one passed four consecutive local runs and all five CI legs, then failed
the API 34 and 35 legs of the next PR with state=COMPLETED rc=0, on a diff
that could not reach it. On a loaded runner the thread that observed
RUNNING can be descheduled long enough for a short encode to finish before
it calls cancel. A longer timeout does not help: the wait already
succeeded.

Two changes, because neither is sufficient alone.

A slower encode. The conversion test now targets WEBM_VP9 at BEST, the
slowest thing FFmpegCommandBuilder emits -- libvpx-vp9 -crf 31 -b:v 0,
with -deadline realtime added only on FAST. Probed on an API 34 emulator:
that session is still RUNNING at 1 s and finished by 2 s, against well
under a second for x265 -preset medium.

A bounded retry. An attempt whose session finished before the cancel
landed has not tested anything, so it is a miss rather than a failure and
is retried; only exhausting five attempts fails, and the message reports
every attempt's state and return code so a real breakage is distinguishable
from a slow machine.

The retry does not soften the test. With FFmpegKit.cancel removed from
both engines, every attempt ends COMPLETED, so both still fail -- verified,
each listing five [state=COMPLETED rc=0] outcomes. Two clean runs
beforehand at 64/0/0/3.

The join test gets the same treatment. It has not flaked yet, but it is
the same mechanism and the same fragility, and finding out on CI again is
not worth the round trip.

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

CLAUDE.md

@@ -130,9 +130,9 @@ install for code that can never run — and on API 37 the full APK does not fit
 - The `model` package is excluded from `ReturnCount` and `CyclomaticComplexMethod` only. It is the
   decision layer, where one branch is one documented user-visible outcome and the metric counts
   answers rather than complexity. Every other rule still applies there.
-- **Coverage is reported, not gated** — **92.8% of lines (2183/2352), 81.3% of branches
-  (1091/1342)**, measured 2026-09-02 with `./gradlew :app:jacocoTestReport`, against 584 JVM tests
-  in 87 classes.
+- **Coverage is reported, not gated** — **94.2% of lines (2234/2372), 87.5% of branches
+  (1171/1338)**, measured 2026-09-05 with `./gradlew :app:jacocoTestReport`, against 628 JVM tests
+  in 96 classes.
 
   **Every figure this file carried before 2026-08-24 was an artifact, roughly half the real one.**
   Robolectric loads classes through its own sandbox classloader with no source location, JaCoCo
@@ -283,6 +283,58 @@ install for code that can never run — and on API 37 the full APK does not fit
   #194 before re-arguing either way — and note the reason it is worth cutting is not coverage but
   that the `runCatching` fallback logs "assuming permissive" while returning empty sets, which makes
   `canEncode` and `canDecode` answer *no* for everything.
+
+  **Wave 4's tests then landed on 2026-09-05**, as #206-#217 for the twelve tickets plus #218
+  (#159) and #219 (#122): 92.8% -> **94.2%** line, 81.3% -> **87.5%** branch, 584 -> 628 tests in 87
+  -> 96 classes. Missed lines 169 -> 138, missed branches 251 -> 167.
+
+  **Its branch move is a different animal from the 2026-08-29 seam work's, and the difference is the
+  point.** That one gained 6.3 branch points with the numerator up 37 (974 -> 1011) while the
+  denominator *fell* 70 (1410 -> 1340) — much of the rise was scaffolding leaving the measurement
+  rather than arms being covered. Here the numerator is up **80** (1091 -> 1171) and
+  the denominator moved **-4** (1342 -> 1338). So this one is almost entirely tests choosing arms
+  nothing had chosen, which is what the entry above warns to check before quoting a branch figure.
+  The line denominator rose the other way, 2352 -> 2372, and that is new production code rather than
+  untested code: the seams the wave cut — `capabilitiesFrom`, `ffprobeInfoFrom`, `sessionOutcome`,
+  and `sweepScope`/`startupSweep`.
+
+  **The two-filter method above is what found the work**, and its second filter earned its place:
+  the largest single gap of the wave (#192, the Cancel button never shown to reach WorkManager) sits
+  on lines that were already green and no line-level filter could see it.
+
+  One result worth carrying forward about *evidence* rather than coverage. #218 fixed a flake whose
+  reproduction is statistical, and running the whole suite six times per arm caught nothing either
+  way — at the observed rate a clean six-run arm is roughly a coin flip, so the comparison was
+  underpowered and proved nothing. What settled it was a deterministic mutation, and then the merge
+  train confirmed it by accident: the race reproduced on #217's Unit tests leg, which sits below
+  #218 and carries the unfixed scope. **Prefer a mutation that must go red to a repetition count**
+  when a fix is for something intermittent.
+
+  **Every number above is `testDebugUnitTest` only, and on 2026-09-05 the instrumented suite got its
+  first read for that reason** — `docs/e2e-read-findings.md`, entries **E1-E6**, tickets
+  **#223-#230**. Four waves had been steered by a figure that **cannot see `app/src/androidTest` at
+  all**, so nothing had ever asked what those 60 device tests pin, only that they were green.
+
+  **It found one test that passes while testing nothing, and it is the one that matters most.**
+  `HardwareFallbackTest` is the only automated check of the hardware→software fallback against a
+  *real* codec failure, and on run `34004304566` the API 33, 34, 35 and 37 legs each log
+  `Routing sample_h264_444.mp4 -> ... via FFMPEG (NO_HARDWARE_ENCODER)` (API 36's logcat artifact on
+  that run is truncated, so it is unread rather than different): emulators expose no
+  hardware encoder, so the job never reaches Media3 and the `catch` it exists to prove is never
+  entered. Its two assertions — succeeded, output non-empty — are true anyway, and it finishes in
+  448 ms. **Deleting that `catch` reddens nothing on any leg** (#223).
+
+  Two things generalise from it. **A test can assert and still not reach**, which no coverage
+  number and no "does it assert something" review would catch — the filter that works is *does this
+  test's premise hold on the machine that runs it?*. And the codebase **already knew**: the sibling
+  `ForcedFailureTest` pins `DeviceCodecs.PERMISSIVE` against exactly this hazard and writes out why,
+  as does `ConversionWorkerTest`. The difference is that their assertions are about the *path*, so
+  without the pin they would fail loudly; `HardwareFallbackTest`'s are about the *output*, so it
+  passes quietly. **Prefer asserting the path over asserting the artefact** where the two differ.
+
+  The read was a triage, not a test push, and five of its six findings are prose rather than code —
+  the suite itself is in good shape. What had drifted is its self-description.
+
 - **Testable code is not done until it is tested.** If a piece is unit testable, it gets unit
   tests before it counts as done. If it is e2e testable, it gets e2e tests. Both clauses apply —
   a change that is both needs both.
@@ -410,4 +462,29 @@ Because versions float, a build can change without a commit. `./gradlew :app:dep
   run instead is `timeout` on the `Test` tasks plus the jstack watchdog beside it in
   `app/build.gradle.kts`, neither of which moves a thread. `HangBoundTest` guards both numbers,
   and **a timed-out run writes no XML for the class that hung** — the dump is its only
-  attribution, so do not delete the watchdog as stray config.
+  attribution, so do not delete the watchdog as stray config. It has since been exercised in anger:
+  on 2026-09-05 it caught #125's Room/WorkManager deadlock on CI, failing in 10m57s with the hung
+  test named, where that ticket had predicted a 60-minute cap and no cause. #125 is closed as
+  bounded on the strength of it — the inversion itself is internal to the two libraries and still
+  live at `work-runtime` 2.11.2 / `room` 2.7.0.
+- **The JVM suite does not run `LibreMediaConverterApp`.** `app/src/test/resources/robolectric.properties`
+  names `TestLibreMediaConverterApp` for every test, and it differs from the real class in exactly
+  one thing: `sweepScope` is `Dispatchers.Unconfined`, so the startup staging sweep finishes before
+  `onCreate()` returns instead of running on `Dispatchers.IO`.
+
+  **That line is load-bearing — do not delete it as stray config.** Robolectric builds an
+  `Application` per test class that asks for one, and each `onCreate` launched a sweep over the
+  shared `<cacheDir>/conversions/` that nothing joined. So a test asserting about a staged file was
+  racing every sweep the classes before it had left in flight (#159). It was CI-only until wave 4
+  added ten Robolectric classes, at which point `OutputPublisherStagingTest` failed on roughly one
+  local run in six. Per-test opt-in was measured and rejected: **27 of the 58 Robolectric classes
+  touch that directory**. The `SupervisorJob` is kept in the test scope so a throwing sweep is
+  swallowed there exactly as in production — the dispatcher is the only intended difference.
+
+  **It cost one assertion, knowingly.** `AppStartSweepTest` used to open by asserting that the
+  manifest's `android:name` is what Robolectric instantiated, so the sweep is code that actually
+  runs. An `application=` override *replaces* the manifest rather than being checked against it, and
+  `applicationInfo.className` reports the override too — measured — so that claim is not merely
+  unasserted on the JVM now, it is unobservable, and a rewritten version would assert the override
+  against itself. **The manifest link is device-only.** What remains is the `as LibreMediaConverterApp`
+  cast in that class's `setUp`, which catches only the test app ceasing to extend the real one.

app/src/androidTest/java/org/libremediaconverter/fallback/HardwareFallbackTest.kt

@@ -12,11 +12,17 @@ import kotlinx.coroutines.withTimeout
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
+import org.junit.Assume.assumeTrue
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
+import org.libremediaconverter.codec.AndroidDeviceCodecs
+import org.libremediaconverter.model.ConversionRequest
+import org.libremediaconverter.model.ConversionRouter
+import org.libremediaconverter.model.Engine
 import org.libremediaconverter.model.OutputFormat
 import org.libremediaconverter.model.QualityTier
+import org.libremediaconverter.model.VideoCodec
 import org.libremediaconverter.work.ConversionWorker
 import java.io.File
 
@@ -34,6 +40,47 @@ import java.io.File
  * hand — a regression test that silently skips is worse than no test, because the count
  * still reads as coverage.
  *
+ * ## Why this skips on emulators, and why that is the honest answer (#223)
+ *
+ * **This test used to pass everywhere while proving nothing.** Two independent facts stop the
+ * fallback happening on an emulator, and both were measured rather than reasoned:
+ *
+ *  1. **The router never sends the job to Media3.** A Fast MP4/H.265 job goes to the hardware path
+ *     only when `device.canEncode(H265)`, and emulators expose no hardware encoder — every leg of
+ *     run `34004304566` logged
+ *     `Routing sample_h264_444.mp4 -> ... via FFMPEG (NO_HARDWARE_ENCODER)`. The whole test
+ *     finished in 448 ms, which is not long enough to fail an export and then re-encode.
+ *  2. **Forcing it to Media3 does not help either, which is the part that settles it.** Pinning
+ *     `ConversionDependencies.deviceCodecs` to [DeviceCodecs.PERMISSIVE] — the trick
+ *     [ForcedFailureTest] uses — makes the router choose Media3, and the export then *succeeds*.
+ *     Measured on a local API 34 emulator: `MediaCodecInfo` logs
+ *     `NoSupport [codec.profileLevel, avc1.F4000C, video/avc]` for **both**
+ *     `c2.goldfish.h264.decoder` and `c2.android.avc.decoder`, and ExoPlayer allocates the
+ *     goldfish decoder anyway, which decodes the file regardless of the profile it declares.
+ *     `c2.android.hevc.encoder` then encodes the result and the job reports `MEDIA3`.
+ *
+ * So the class KDoc above — "Media3 fails partway through the export on every device" — **is not
+ * true of the emulator images**, and no amount of routing pressure makes this fixture force a
+ * fallback there. The emulator cannot answer this question, so the test says so out loud instead
+ * of passing.
+ *
+ * That is why the gate is [assumeTrue] on the *production* premise (`canEncode(H265)`) rather than
+ * a pinned profile: pinning would also swap in software codecs, which is not the path a real
+ * device takes and is what made the forced run succeed. **This is now the third permanent skip**;
+ * the other two are [org.libremediaconverter.bench.RealMediaBenchmark]'s.
+ *
+ * `ForcedFailureTest.hardwareFailureFallsBackToSoftware` still covers the fallback *wiring* on
+ * every leg, with an `ExplodingHardware` double. What only a device with a real hardware encoder
+ * can show is two real engines disagreeing about a real file, and that is what this is for.
+ *
+ * ## Why the assertion is a pair
+ *
+ * `KEY_ENGINE_USED` is `FFMPEG` whether the fallback fired **or** the router went straight there,
+ * so asserting it alone would not have caught any of the above. The premise is asserted
+ * separately: [ConversionRouter.route] chooses `MEDIA3` for this request on this device. Static
+ * routing wanted hardware, the runtime result was software — together, and only together, that is
+ * the fallback.
+ *
  * The fixture was produced with x264, which the host toolchain cannot do (Fedora's
  * ffmpeg ships openh264, which is Constrained Baseline only):
  *
@@ -66,6 +113,15 @@ class HardwareFallbackTest {
 
     @Test
     fun aFileMedia3CannotDecodeStillConvertsViaFfmpeg(): Unit = runBlocking {
+        // See "Why this skips on emulators" on the class. Without a real hardware encoder the
+        // router never chooses Media3, and forcing it makes the export succeed instead of fail --
+        // so there is no fallback to observe and a green run would mean nothing.
+        assumeTrue(
+            "no hardware HEVC encoder, so the router cannot choose Media3 and there is no " +
+                "fallback to exercise",
+            AndroidDeviceCodecs.get().canEncode(VideoCodec.H265),
+        )
+
         val request = ConversionWorker.request(
             inputUri = Uri.fromFile(input),
             displayName = SAMPLE,
@@ -75,6 +131,19 @@ class HardwareFallbackTest {
             // the tier where the fallback has to rescue the conversion.
             quality = QualityTier.FAST,
         )
+        // The premise, asserted rather than assumed: this request is one the router wants to send
+        // to hardware on this device. Without it the test is green whether the fallback fired or
+        // the job never went near Media3, which is exactly how #223 stayed invisible.
+        val decision = ConversionRouter.route(
+            ConversionRequest(OutputFormat.MP4_H265.spec, quality = QualityTier.FAST),
+            AndroidDeviceCodecs.get(),
+        )
+        assertEquals(
+            "this test only means something if the router sends this job to Media3",
+            Engine.MEDIA3,
+            decision.engine,
+        )
+
         workManager.enqueue(request).result.get()
 
         val terminal = withTimeout(TIMEOUT_MS) {
@@ -88,6 +157,14 @@ class HardwareFallbackTest {
             terminal?.state,
         )
 
+        // The outcome. Paired with the routing assertion above this is the fallback and nothing
+        // else: hardware was chosen, software is what ran.
+        assertEquals(
+            "the router chose Media3, so a successful job must have fallen back to FFmpeg",
+            Engine.FFMPEG.name,
+            terminal?.outputData?.getString(ConversionWorker.KEY_ENGINE_USED),
+        )
+
         val out = File(terminal!!.outputData.getString(ConversionWorker.KEY_OUTPUT_PATH)!!)
         assertTrue("no output produced", out.exists() && out.length() > 0)
         out.delete()

app/src/androidTest/java/org/libremediaconverter/ffmpeg/FFmpegEngineTest.kt

@@ -4,10 +4,20 @@ import android.media.MediaExtractor
 import android.media.MediaFormat
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
+import com.arthenica.ffmpegkit.FFmpegKit
+import com.arthenica.ffmpegkit.FFmpegSession
+import com.arthenica.ffmpegkit.ReturnCode
+import com.arthenica.ffmpegkit.SessionState
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.cancelAndJoin
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
 import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeout
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
+import org.junit.Assert.fail
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -113,6 +123,11 @@ class FFmpegEngineTest {
     fun encodesFlacLosslessAudio() {
         val out = convert(OutputFormat.FLAC)
         assertTrue("no FLAC produced", out.exists() && out.length() > 0)
+        // "fLaC", the native FLAC stream marker. Without this the test passed on any non-empty
+        // file, so a builder arm emitting the wrong encoder into a .flac name shipped green
+        // (#228) -- the same shape the five assertions above already guard against.
+        val magic = out.inputStream().use { String(it.readNBytes(4), Charsets.US_ASCII) }
+        assertEquals("fLaC", magic)
     }
 
     @Test
@@ -127,6 +142,165 @@ class FFmpegEngineTest {
     fun encodesOpus() {
         val out = convert(OutputFormat.OPUS)
         assertTrue("no Opus produced", out.exists() && out.length() > 0)
+        // OutputFormat.OPUS is Container.OGG, so the file is an Ogg stream: "OggS" (#228).
+        // Deliberately the container marker rather than the codec -- it is what the other
+        // container-level assertions in this class check, and it is four bytes at offset 0.
+        val magic = out.inputStream().use { String(it.readNBytes(4), Charsets.US_ASCII) }
+        assertEquals("OggS", magic)
+    }
+
+    /**
+     * The percentage itself, which every other test in this class computes and none of them reads.
+     *
+     * `FFmpegEngine` derives progress as `stats.time / durationMs * 100`, and the statistics
+     * callback runs on every conversion here — but every call site omits `onProgress`, so until
+     * this test nothing on any source set had ever looked at the number (#229). #196 covered the
+     * *worker's* progress lambda, and did it with a fake engine that reports whatever the test
+     * tells it to; `ProgressNotificationTest` covers throttling the same way. The arithmetic was
+     * the one part with no reader.
+     *
+     * ## Why the duration is deliberately wrong
+     *
+     * `sample_h264.mp4` is exactly 3.000 s, and this passes **30 s** as the duration. So the
+     * conversion still encodes the whole clip, `stats.time` still climbs to about 3000 ms, and the
+     * reported percentage tops out around **10** rather than 100.
+     *
+     * That is what makes the assertion bite. A range check alone is worthless here: replacing
+     * `percent` with a constant `0` satisfies "every value is in 0..100" and "the values never go
+     * backwards", and so does a list of `[0, 100]`. Pinning the *band* rejects every constant, and
+     * — because the band is a tenth of the way up — it also rejects an implementation that ignores
+     * `durationMs`, which would report ~100 for the same run.
+     *
+     * The bound is deliberately loose (5..25 for an expected 10). The last statistics callback can
+     * land slightly before the final frame, so the peak is "about 3000 ms of a claimed 30 000",
+     * not exactly it.
+     */
+    @Test
+    fun progressIsReportedAsAFractionOfTheDurationItWasGiven() {
+        val seen = mutableListOf<Int>()
+        val out = outputFor("out_progress.mp4")
+        runBlocking {
+            engine.run(
+                request = ConversionRequest(spec = OutputFormat.MP4_H264.spec, quality = QualityTier.BEST),
+                inputPath = input.absolutePath,
+                output = out,
+                // Ten times the fixture's real 3 s. See the KDoc.
+                durationMs = 30_000,
+                onProgress = { percent -> seen += percent },
+            )
+        }
+
+        assertTrue("the statistics callback never reported progress", seen.isNotEmpty())
+        assertTrue("progress out of range: $seen", seen.all { it in 0..100 })
+        assertEquals("progress went backwards: $seen", seen.sorted(), seen)
+        // The band. Rejects any constant, and rejects ignoring durationMs (which would read ~100).
+        val peak = seen.max()
+        assertTrue(
+            "3 s of media against a claimed 30 s should peak near 10%, got $peak from $seen",
+            peak in 5..25,
+        )
+    }
+
+    /**
+     * Cancelling a *running* conversion actually stops the native session.
+     *
+     * Nothing on any source set did this before (#224). Every `cancel` in `app/src/androidTest` is
+     * `WorkManager.cancelWorkById` against work that is **queued or already finished** — the two in
+     * `ReattachOnLaunchTest` cancel a job carrying a one-hour initial delay, and one immediately
+     * after enqueue. On the JVM, `WorkerCancellationTest` and `HardwareFallbackTest`'s cancellation
+     * case drive a `SoftwareTranscoder` double that records the call. No test had ever asked a real
+     * native session to stop. This is `docs/defect-audit.md` **D10**'s forcing condition.
+     *
+     * It is the one path where cancelling wrong is silently expensive rather than loudly broken: a
+     * missed `FFmpegKit.cancel` leaves the native process encoding to completion while the UI says
+     * the job is cancelled, and nothing reports the battery and thermal cost.
+     *
+     * ## Why the assertion is the session's return code, not the output file
+     *
+     * The obvious assertion — the partial output is gone — **cannot fail**, so it would have been a
+     * vacuous test. `invokeOnCancellation` deletes the path, and on POSIX unlinking a file ffmpeg
+     * still holds open leaves ffmpeg writing to the unlinked inode; the path stays gone whether or
+     * not the cancel ever reached the session. Deleting `FFmpegKit.cancel` and keeping
+     * `output.delete()` passes that check every time.
+     *
+     * What distinguishes them is the session's own verdict: a cancelled session ends with the
+     * cancel return code, a completed one ends successfully. That is a fact about the session
+     * rather than about timing, so it is read *after* waiting for the session to leave
+     * [SessionState.RUNNING] rather than at a fixed delay.
+     *
+     * ## Why it cancels on RUNNING rather than on the first progress callback
+     *
+     * Measured. Cancelling from the first `onProgress` was tried first and **failed on a local API
+     * 34 emulator with `state=COMPLETED rc=0`** — every committed fixture is 2-3 s at 320x240, and
+     * the encode finishes before the first statistics callback has been delivered and acted on. The
+     * progress callback proves the session is running, but arrives too late to interrupt anything.
+     * `FFmpegKit.listSessions` shows the session [SessionState.RUNNING] far earlier.
+     *
+     * ## Why it retries, which is the part that took two attempts to get right
+     *
+     * Waiting for `RUNNING` is not on its own enough. With `MP4_H265` at [QualityTier.BEST] this
+     * passed four consecutive local runs and all five CI legs, then failed on the API 34 and 35 legs
+     * of the next PR with `state=COMPLETED rc=0`. Nothing had changed: on a loaded runner the thread
+     * that observed `RUNNING` can be descheduled long enough for a short encode to finish before it
+     * calls `cancel`. A longer timeout does not help — the wait already succeeded.
+     *
+     * Two changes together, because neither is sufficient:
+     *
+     *  - **A slower encode.** `WEBM_VP9` at `BEST` is the slowest thing this builder emits:
+     *    `libvpx-vp9 -crf 31 -b:v 0`, with `-deadline realtime` added **only** on
+     *    [QualityTier.FAST]. Probed on an API 34 emulator, that session is still `RUNNING` at 1 s
+     *    and finished by 2 s, against well under a second for x265 `-preset medium`.
+     *  - **Retrying the attempt.** An attempt whose session finished before the cancel landed has
+     *    not tested anything, so it is not a failure — it is a miss, and it is retried. Only
+     *    exhausting [CANCEL_ATTEMPTS] is a failure, and its message says which case it hit.
+     *
+     * That keeps the mutation honest: with `FFmpegKit.cancel` removed **every** attempt ends
+     * `COMPLETED`, so the test still fails — it just takes [CANCEL_ATTEMPTS] tries to say so.
+     *
+     * The session is identified by diffing against the ids present before each attempt, because
+     * this class has already produced eight of them by the time this executes.
+     */
+    @Test
+    fun cancellingARunningConversionCancelsTheNativeSession(): Unit = runBlocking {
+        val outcomes = mutableListOf<String>()
+
+        repeat(CANCEL_ATTEMPTS) { attempt ->
+            val before = FFmpegKit.listSessions().map { it.getSessionId() }.toSet()
+            val out = outputFor("out_cancelled_$attempt.webm")
+
+            val job = launch(Dispatchers.IO) {
+                engine.run(
+                    // The slowest target this builder emits -- see the KDoc. Not decoration:
+                    // with a faster one this loses the race on a loaded CI runner.
+                    request = ConversionRequest(spec = OutputFormat.WEBM_VP9.spec, quality = QualityTier.BEST),
+                    inputPath = input.absolutePath,
+                    output = out,
+                    durationMs = 3_000,
+                )
+            }
+
+            val ours = withTimeout(TIMEOUT_MS) {
+                var found: FFmpegSession? = null
+                while (found == null) {
+                    found = FFmpegKit.listSessions().firstOrNull { it.getSessionId() !in before }
+                    if (found == null) delay(POLL_MS)
+                }
+                found
+            }
+            job.cancelAndJoin()
+            withTimeout(TIMEOUT_MS) {
+                while (ours.getState() == SessionState.RUNNING) delay(POLL_MS)
+            }
+
+            if (ReturnCode.isCancel(ours.getReturnCode())) return@runBlocking
+            // The encode beat us to it. That attempt proved nothing either way, so try again.
+            outcomes += "state=${ours.getState()} rc=${ours.getReturnCode()}"
+        }
+
+        fail(
+            "never interrupted a running session in $CANCEL_ATTEMPTS attempts, so either every " +
+                "encode finished first or cancellation does not reach it: $outcomes",
+        )
     }
 
     // --- the quality tier the GPL licence was taken for --------------------
@@ -166,4 +340,19 @@ class FFmpegEngineTest {
         }.exceptionOrNull()
         assertTrue("expected an FFmpegException, got $failure", failure is FFmpegEngine.FFmpegException)
     }
+
+    private companion object {
+        /** Generous: it bounds a hang, and every wait here normally settles in well under a second. */
+        const val TIMEOUT_MS = 30_000L
+        const val POLL_MS = 50L
+
+        /**
+         * How many times to try to catch the session mid-encode.
+         *
+         * Each miss costs about the length of one VP9 encode -- a second or two -- and a miss is
+         * the loaded-runner case rather than a defect. Five is enough that exhausting them means
+         * cancellation is not reaching the session, which is what the failure message says.
+         */
+        const val CANCEL_ATTEMPTS = 5
+    }
 }

app/src/androidTest/java/org/libremediaconverter/join/ConcatEngineTest.kt

@@ -5,10 +5,20 @@ import android.media.MediaFormat
 import android.net.Uri
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
+import com.arthenica.ffmpegkit.FFmpegKit
+import com.arthenica.ffmpegkit.FFmpegSession
+import com.arthenica.ffmpegkit.ReturnCode
+import com.arthenica.ffmpegkit.SessionState
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.cancelAndJoin
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
 import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeout
 import org.junit.After
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
+import org.junit.Assert.fail
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -16,6 +26,7 @@ import org.libremediaconverter.convert.MediaProbe
 import org.libremediaconverter.convert.StagingNames
 import org.libremediaconverter.ffmpeg.ConcatEngine
 import org.libremediaconverter.model.ConcatStrategy
+import org.libremediaconverter.work.ConcatWorker
 import java.io.File
 
 /**
@@ -50,6 +61,82 @@ class ConcatEngineTest {
         (staged + listOf(clipA, clipB, clipMismatched)).forEach { it.delete() }
     }
 
+    /**
+     * Cancelling a *running* join actually stops the native session.
+     *
+     * The `FFmpegEngine` half of #224 landed first (PR #236); this is the same gap in
+     * [ConcatEngine]. Before these two, no test on any source set had ever asked a real native
+     * session to stop — every `cancel` in `app/src/androidTest` targets WorkManager entries that
+     * are queued or already finished.
+     *
+     * ## Two things carried over from the conversion side, both measured there
+     *
+     * **The assertion is the session's return code.** A cancelled session ends with the cancel
+     * code, a completed one does not. The alternative — checking the output file — is even less
+     * available here than it was for conversions: [ConcatEngine] does not delete its output on
+     * cancellation at all. Its `invokeOnCancellation` is `FFmpegKit.cancel(...)` and nothing else,
+     * where [org.libremediaconverter.ffmpeg.FFmpegEngine]'s also deletes the partial. Whether that
+     * asymmetry is deliberate is a separate question from this test, which is why this asserts the
+     * thing that is true of both.
+     *
+     * **The cancel is triggered on [SessionState.RUNNING], not on progress.** `ConcatWorker`
+     * publishes no progress at all, so there is no callback to hang it on even in principle — but
+     * the conversion side established the deeper reason: the committed clips are 2 s at 320x240 and
+     * the encode outruns a callback-triggered cancel.
+     *
+     * **And the attempt is retried**, for the reason the conversion side measured the hard way: on
+     * a loaded runner the thread that observed `RUNNING` can be descheduled long enough for a short
+     * encode to finish before it calls `cancel`, which failed two CI legs there. An attempt whose
+     * session finished first has tested nothing, so it is a miss rather than a failure; only
+     * exhausting [CANCEL_ATTEMPTS] fails, and with `FFmpegKit.cancel` removed every attempt misses,
+     * so the mutation still bites.
+     *
+     * The inputs are deliberately the **mismatched** pair, so [ConcatStrategy.REENCODE] is chosen.
+     * A stream copy of two short clips is close to instantaneous and would leave nothing to
+     * interrupt; re-encoding is the case where a user would actually reach for Cancel.
+     *
+     * *Mutation:* drop `FFmpegKit.cancel(session.getSessionId())` from `ConcatEngine`'s
+     * `invokeOnCancellation` — the session runs to completion and this fails.
+     */
+    @Test
+    fun cancellingARunningJoinCancelsTheNativeSession(): Unit = runBlocking {
+        val outcomes = mutableListOf<String>()
+
+        repeat(CANCEL_ATTEMPTS) { attempt ->
+            val before = FFmpegKit.listSessions().map { it.getSessionId() }.toSet()
+            val out = output("cancelled_join_$attempt.mp4")
+
+            val job = launch(Dispatchers.IO) {
+                engine.join(
+                    listOf(Uri.fromFile(clipA), Uri.fromFile(clipMismatched)),
+                    out,
+                    ConcatWorker.DEFAULT_FORMAT,
+                )
+            }
+
+            val ours = withTimeout(TIMEOUT_MS) {
+                var found: FFmpegSession? = null
+                while (found == null) {
+                    found = FFmpegKit.listSessions().firstOrNull { it.getSessionId() !in before }
+                    if (found == null) delay(POLL_MS)
+                }
+                found
+            }
+            job.cancelAndJoin()
+            withTimeout(TIMEOUT_MS) {
+                while (ours.getState() == SessionState.RUNNING) delay(POLL_MS)
+            }
+
+            if (ReturnCode.isCancel(ours.getReturnCode())) return@runBlocking
+            outcomes += "state=${ours.getState()} rc=${ours.getReturnCode()}"
+        }
+
+        fail(
+            "never interrupted a running join in $CANCEL_ATTEMPTS attempts, so either every " +
+                "encode finished first or cancellation does not reach it: $outcomes",
+        )
+    }
+
     private fun copyAsset(name: String): File {
         val out = File(context.cacheDir, name)
         InstrumentationRegistry.getInstrumentation().context.assets
@@ -180,4 +267,13 @@ class ConcatEngineTest {
             a.width != mismatched.width || a.height != mismatched.height,
         )
     }
+
+    private companion object {
+        /** Generous: it bounds a hang, and both waits here normally settle in well under a second. */
+        const val TIMEOUT_MS = 30_000L
+        const val POLL_MS = 50L
+
+        /** See the conversion side: a miss is the loaded-runner case, not a defect. */
+        const val CANCEL_ATTEMPTS = 5
+    }
 }

app/src/androidTest/java/org/libremediaconverter/saf/SafPickerRoundTripTest.kt

@@ -10,6 +10,9 @@ import androidx.compose.ui.test.performClick
 import androidx.media3.common.util.UnstableApi
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
+import androidx.test.runner.lifecycle.ActivityLifecycleCallback
+import androidx.test.runner.lifecycle.ActivityLifecycleMonitorRegistry
+import androidx.test.runner.lifecycle.Stage
 import androidx.test.uiautomator.By
 import androidx.test.uiautomator.BySelector
 import androidx.test.uiautomator.Configurator
@@ -24,6 +27,7 @@ import org.junit.runner.RunWith
 import org.libremediaconverter.FailsOnEmulatorApi37
 import org.libremediaconverter.MainActivity
 import org.libremediaconverter.ui.TestTags
+import java.util.concurrent.atomic.AtomicInteger
 
 /**
  * Choosing a file, through the real system picker, and still having it after a rotation.
@@ -203,6 +207,8 @@ import org.libremediaconverter.ui.TestTags
  * driven there at all. That is why this gap survived as long as it did.
  * `tools/local-emulator/run-e2e.sh` runs API 33-36 on the development host, and both tests pass
  * there: **59 / 0 / 0 / 2 at API 33 and again at API 36**, whole suite, 2026-08-24.
+ * (Since #223 the skip column reads 3 on an emulator — `HardwareFallbackTest` now announces
+ * that it cannot run without a hardware HEVC encoder rather than passing vacuously.)
  *
  * ### Why only the rotation test carries [FailsOnEmulatorApi37]
  *
@@ -251,6 +257,21 @@ class SafPickerRoundTripTest {
     /** Set by the one test that rotates, read by [restoreOrientation]. See its KDoc. */
     private var rotated = false
 
+    /** Counts [MainActivity] creations from the moment [watchForRecreation] is called. */
+    private val recreations = AtomicInteger()
+
+    /**
+     * Counts a rotation's recreation without asking the Activity anything.
+     *
+     * Deliberately not `composeRule.activity`, which resolves through `scenario.onActivity` and so
+     * blocks on the main thread. Polling *that* across a recreation is a plausible reading of the
+     * 20-minute wedges in #122, which would make the obvious barrier the bug it is meant to fix.
+     * The runner's lifecycle monitor is a callback: reading the counter touches no looper.
+     */
+    private val recreationWatcher = ActivityLifecycleCallback { activity, stage ->
+        if (activity is MainActivity && stage == Stage.CREATED) recreations.incrementAndGet()
+    }
+
     /**
      * Leave the device the way it was found — and only if this test moved it.
      *
@@ -270,6 +291,7 @@ class SafPickerRoundTripTest {
      */
     @After
     fun restoreOrientation() {
+        ActivityLifecycleMonitorRegistry.getInstance().removeLifecycleCallback(recreationWatcher)
         if (!rotated) return
         device.setOrientationNatural()
         device.unfreezeRotation()
@@ -303,9 +325,11 @@ class SafPickerRoundTripTest {
         // The identity hash rather than the Activity itself, so nothing here keeps a destroyed
         // Activity reachable across the recreation it is being used to detect.
         val before = System.identityHashCode(composeRule.activity)
+        watchForRecreation()
 
         device.setOrientationLandscape()
         rotated = true
+        awaitRecreation()
         composeRule.waitForIdle()
 
         // Two guards before the assertion that matters, because both of the ways this test could
@@ -675,6 +699,36 @@ class SafPickerRoundTripTest {
      * `Condition still not satisfied after 30000 ms` — which names neither the node nor the test.
      * With the description it says which affordance never arrived, which is the whole finding.
      */
+    /** Starts counting [MainActivity] creations, so [awaitRecreation] can wait for the next one. */
+    private fun watchForRecreation() {
+        recreations.set(0)
+        ActivityLifecycleMonitorRegistry.getInstance().addLifecycleCallback(recreationWatcher)
+    }
+
+    /**
+     * Waits for the rotation to actually rebuild [MainActivity], which `waitForIdle` does not.
+     *
+     * **This is #122.** `waitForIdle()` waits for the compose hierarchy to settle. Immediately
+     * after a rotation the window manager has accepted but not yet delivered as a configuration
+     * change, the *old* Activity's composition is already idle — so it returns, `composeRule
+     * .activity` still resolves to the old instance, and the guard below reads an unchanged
+     * identity hash. That is the clean `AssertionError` seen on the API 33 gating leg of #217, and
+     * the wedges on #122 are the same race taken the other way: land while the composition is
+     * being torn down and there is nothing coherent for `waitForIdle` to settle on.
+     *
+     * A bounded wait is worth having even if that second half is wrong. It turns a 20-minute
+     * `WEDGE_TIMEOUT` — which costs the leg and names no test — into a fast failure that says which
+     * test and what it was waiting for.
+     */
+    private fun awaitRecreation() {
+        composeRule.waitUntil(
+            "the rotation did not recreate MainActivity within $RECREATION_TIMEOUT_MS ms",
+            RECREATION_TIMEOUT_MS,
+        ) {
+            recreations.get() > 0
+        }
+    }
+
     private fun awaitNode(tag: String) {
         composeRule.waitUntil("a node tagged $tag exists", APP_TIMEOUT_MS) {
             composeRule.onAllNodesWithTag(tag).fetchSemanticsNodes().isNotEmpty()
@@ -703,6 +757,15 @@ class SafPickerRoundTripTest {
          */
         const val REOPENED_TIMEOUT_MS = 10_000L
 
+        /**
+         * How long a rotation is given to destroy and rebuild the Activity.
+         *
+         * Generous against the API 33 and 34 emulators #122 was measured on, where the rotation is
+         * slow enough for the gap this bound exists to cover to be observable at all — and still
+         * two orders of magnitude inside the 1200 s `WEDGE_TIMEOUT` it replaces.
+         */
+        const val RECREATION_TIMEOUT_MS = 15_000L
+
         /**
          * How long the app is given to take the window focus back after a back press.
          *

app/src/androidTest/java/org/libremediaconverter/work/NotificationCancelActionTest.kt

@@ -0,0 +1,129 @@
+package org.libremediaconverter.work
+
+import android.net.Uri
+import androidx.media3.common.util.UnstableApi
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.WorkInfo
+import androidx.work.WorkManager
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeout
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotNull
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremediaconverter.model.OutputFormat
+import org.libremediaconverter.model.QualityTier
+import java.io.File
+import java.util.concurrent.TimeUnit
+
+/**
+ * The Cancel button in the notification shade actually cancels the job.
+ *
+ * `ConversionNotifications.build` attaches one action, wired to
+ * `WorkManager.createCancelPendingIntent(id)`. Before this test `createCancelPendingIntent` had
+ * **no references anywhere outside its own declaration** — no JVM test, no instrumented test
+ * (#227).
+ *
+ * That matters more than an ordinary uncovered line. A conversion runs in a foreground service and
+ * the user is invited to leave the app; once they do, this action is the only way to stop it. If
+ * the `PendingIntent` carries the wrong id, the button does nothing, the notification stays, and
+ * the job runs to completion — with no error, no log, and no screen to look at.
+ *
+ * ## Why this fires the intent rather than reading the shade
+ *
+ * The obvious version asks `NotificationManager.getActiveNotifications()` for id 1001 and taps what
+ * it finds. That was rejected: the instrumented suite grants no runtime permissions, so
+ * `POST_NOTIFICATIONS` is denied throughout, and whether a suppressed foreground-service
+ * notification is returned there is a platform detail that varies — the test would be asserting
+ * something about notification *visibility* rather than about cancellation.
+ *
+ * The `PendingIntent` is the subject; where it is read from is incidental. Building the
+ * notification for a real, live work id and firing its action exercises exactly the thing that can
+ * be wrong — a real `PendingIntent` dispatch reaching real `WorkManager` — and does it the same way
+ * on every API level.
+ *
+ * ## Why the job is delayed rather than running
+ *
+ * A conversion of the committed 3 s fixture finishes in well under a second on an emulator
+ * (`HardwareFallbackTest` completed one in 448 ms), so racing a cancel against a running job would
+ * be flaky in the direction that fails. An initial delay keeps the job reliably `ENQUEUED`, which
+ * is a state `cancelWorkById` acts on identically — what is under test is whether firing the action
+ * reaches WorkManager with the right id, not which state it interrupts.
+ *
+ * *Mutation:* build the `PendingIntent` from `UUID.randomUUID()` instead of the request's id. The
+ * notification looks identical and the job is never cancelled.
+ */
+@UnstableApi
+@RunWith(AndroidJUnit4::class)
+class NotificationCancelActionTest {
+
+    private val context = InstrumentationRegistry.getInstrumentation().targetContext
+    private val workManager = WorkManager.getInstance(context)
+    private lateinit var input: File
+
+    @Before
+    fun setUp() {
+        input = File(context.cacheDir, "cancel_action_sample.mp4")
+        InstrumentationRegistry.getInstrumentation().context.assets
+            .open("sample_h264.mp4")
+            .use { asset -> input.outputStream().use { asset.copyTo(it) } }
+    }
+
+    @After
+    fun tearDown() {
+        input.delete()
+        File(context.cacheDir, "conversions").listFiles()?.forEach { it.delete() }
+    }
+
+    @Test
+    fun theNotificationsCancelActionCancelsThatJob(): Unit = runBlocking {
+        val request = ConversionWorker.request(
+            inputUri = Uri.fromFile(input),
+            displayName = input.name,
+            sizeBytes = input.length(),
+            spec = OutputFormat.MP4_H264.spec,
+            quality = QualityTier.FAST,
+        ).let { base ->
+            // Rebuild with a delay so the job stays ENQUEUED for the whole test. See the KDoc.
+            OneTimeWorkRequestBuilder<ConversionWorker>()
+                .setInputData(base.workSpec.input)
+                .setInitialDelay(1, TimeUnit.HOURS)
+                .build()
+        }
+        workManager.enqueue(request).result.get()
+
+        // The job is queued and waiting, which is the state the cancel has to interrupt.
+        assertEquals(
+            WorkInfo.State.ENQUEUED,
+            withTimeout(TIMEOUT_MS) {
+                workManager.getWorkInfoByIdFlow(request.id).first { it != null }
+            }?.state,
+        )
+
+        val notification = ConversionNotifications(context)
+            .build(request.id, title = input.name, percent = 0, indeterminate = true)
+        val action = notification.actions?.firstOrNull()
+        assertNotNull("the progress notification carries no action to cancel with", action)
+
+        // The whole point: fire it the way the shade would, and see the job stop.
+        action!!.actionIntent.send()
+
+        val terminal = withTimeout(TIMEOUT_MS) {
+            workManager.getWorkInfoByIdFlow(request.id).first { it != null && it.state.isFinished }
+        }
+        assertEquals(
+            "firing the notification's Cancel action must cancel the job it was built for",
+            WorkInfo.State.CANCELLED,
+            terminal?.state,
+        )
+    }
+
+    private companion object {
+        const val TIMEOUT_MS = 30_000L
+    }
+}

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

@@ -3,6 +3,7 @@ package org.libremediaconverter
 import android.app.Application
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
 import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.launch
 import org.libremediaconverter.convert.OutputPublisher
@@ -17,14 +18,36 @@ import org.libremediaconverter.convert.OutputPublisher
  * ever becomes a `Converted` state, or a `reset()`'s delete is cancelled along with the
  * Activity. Process start is the one moment those leftovers are reliably observable.
  */
-class LibreMediaConverterApp : Application() {
+open class LibreMediaConverterApp : Application() {
 
     /**
      * Deliberately process-lifetime and never cancelled: the work it carries is a single
      * short task that should outlive nothing in particular and be interrupted by nothing.
      * A `SupervisorJob` so a failure here could never take a sibling down with it.
+     *
+     * **`protected open` for #159.** Robolectric builds an `Application` for every test that asks
+     * for one, so on the JVM this is not one background sweep but one *per test* — all of them on
+     * `Dispatchers.IO`, all touching the same `cacheDir`, none of them joined by anything. That is
+     * a race against any test asserting about a file under `conversions/`, and it grew with the
+     * suite: wave 4 added ten Robolectric classes and took it from CI-only to roughly one local run
+     * in six. The JVM suite substitutes a scope that runs the sweep inline — see
+     * `app/src/test/resources/robolectric.properties` and `TestLibreMediaConverterApp`.
+     *
+     * A constructor parameter would be the ordinary way to inject this and is not available: the
+     * framework builds this class, so the seam has to be a member.
      */
-    private val appScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    protected open val sweepScope: CoroutineScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+
+    /**
+     * The sweep [onCreate] last started, so a caller that needs it finished can wait for it.
+     *
+     * Nothing in production reads this — process start does not wait for its own housekeeping. It
+     * exists because the alternative for a test is a timed poll, and a poll cannot tell "the sweep
+     * has not run yet" from "the sweep ran and did nothing".
+     */
+    @Volatile
+    var startupSweep: Job? = null
+        private set
 
     override fun onCreate() {
         super.onCreate()
@@ -53,6 +76,6 @@ class LibreMediaConverterApp : Application() {
         //
         // sweepStaging() also re-reads each timestamp immediately before deleting, which
         // closes the window between listing the directory and acting on the listing.
-        appScope.launch { OutputPublisher(this@LibreMediaConverterApp).sweepStaging() }
+        startupSweep = sweepScope.launch { OutputPublisher(this@LibreMediaConverterApp).sweepStaging() }
     }
 }

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/main/java/org/libremediaconverter/ffmpeg/ConcatEngine.kt

@@ -5,7 +5,6 @@ import android.net.Uri
 import android.util.Log
 import com.arthenica.ffmpegkit.FFmpegKit
 import com.arthenica.ffmpegkit.FFmpegKitConfig
-import com.arthenica.ffmpegkit.ReturnCode
 import kotlinx.coroutines.suspendCancellableCoroutine
 import org.libremediaconverter.convert.ConcatJoiner
 import org.libremediaconverter.convert.MediaProbe
@@ -66,16 +65,16 @@ class ConcatEngine(private val context: Context) : ConcatJoiner {
     private suspend fun execute(args: List<String>) = suspendCancellableCoroutine { cont ->
         Log.i(TAG, "ffmpeg ${args.joinToString(" ")}")
         val session = FFmpegKit.executeWithArgumentsAsync(args.toTypedArray()) { completed ->
-            val rc = completed.getReturnCode()
-            when {
-                ReturnCode.isSuccess(rc) -> cont.resume(Unit)
-                ReturnCode.isCancel(rc) -> cont.cancel()
-                else -> cont.resumeWithException(
-                    FFmpegEngine.FFmpegException(
-                        "Joining failed (${rc?.value}): " +
-                            completed.getAllLogsAsString(LOG_TAIL_LIMIT).orEmpty(),
-                    ),
-                )
+            val outcome = sessionOutcome(
+                rc = completed.getReturnCode(),
+                prefix = "Joining",
+                failStackTrace = { completed.getFailStackTrace() },
+                logTail = { completed.getAllLogsAsString(LOG_TAIL_LIMIT) },
+            )
+            when (outcome) {
+                SessionOutcome.Success -> cont.resume(Unit)
+                SessionOutcome.Cancelled -> cont.cancel()
+                is SessionOutcome.Failed -> cont.resumeWithException(FFmpegEngine.FFmpegException(outcome.message))
             }
         }
         cont.invokeOnCancellation { FFmpegKit.cancel(session.getSessionId()) }

app/src/main/java/org/libremediaconverter/ffmpeg/FFmpegEngine.kt

@@ -4,7 +4,6 @@ import android.util.Log
 import com.arthenica.ffmpegkit.FFmpegKit
 import com.arthenica.ffmpegkit.FFmpegKitConfig
 import com.arthenica.ffmpegkit.Level
-import com.arthenica.ffmpegkit.ReturnCode
 import kotlinx.coroutines.suspendCancellableCoroutine
 import org.libremediaconverter.convert.SoftwareTranscoder
 import org.libremediaconverter.model.ConversionRequest
@@ -51,19 +50,16 @@ class FFmpegEngine : SoftwareTranscoder {
         val session = FFmpegKit.executeWithArgumentsAsync(
             args.toTypedArray(),
             { completed ->
-                val rc = completed.getReturnCode()
-                when {
-                    ReturnCode.isSuccess(rc) -> cont.resume(Unit)
-                    ReturnCode.isCancel(rc) ->
-                        cont.cancel()
-                    else -> cont.resumeWithException(
-                        FFmpegException(
-                            "FFmpeg failed (${rc?.value}): " +
-                                completed.getFailStackTrace().orEmpty().ifBlank {
-                                    completed.getAllLogsAsString(LOG_TAIL_LIMIT).orEmpty()
-                                },
-                        ),
-                    )
+                val outcome = sessionOutcome(
+                    rc = completed.getReturnCode(),
+                    prefix = "FFmpeg",
+                    failStackTrace = { completed.getFailStackTrace() },
+                    logTail = { completed.getAllLogsAsString(LOG_TAIL_LIMIT) },
+                )
+                when (outcome) {
+                    SessionOutcome.Success -> cont.resume(Unit)
+                    SessionOutcome.Cancelled -> cont.cancel()
+                    is SessionOutcome.Failed -> cont.resumeWithException(FFmpegException(outcome.message))
                 }
             },
             { log -> Log.d(TAG, log.message.trimEnd()) },

app/src/main/java/org/libremediaconverter/ffmpeg/SessionOutcome.kt

@@ -0,0 +1,54 @@
+package org.libremediaconverter.ffmpeg
+
+import com.arthenica.ffmpegkit.ReturnCode
+
+/**
+ * What a finished FFmpegKit session means, as a function of its return code.
+ *
+ * Both engines had their own copy of this `when`, twelve lines apart in two files, and the copies
+ * had drifted: [FFmpegEngine] preferred the fail stack trace and fell back to the log tail, while
+ * [ConcatEngine] only ever read the log tail. Neither was tested — both live inside a callback
+ * handed to `FFmpegKit`, which does not run on the JVM — so the divergence was invisible.
+ *
+ * #203 decided to unify on the stack trace, so a join failure now carries the diagnostics a
+ * conversion failure always did. The *prefix* stays per-engine: unifying the strategy must not
+ * unify the sentence, since "FFmpeg failed" and "Joining failed" describe different jobs.
+ */
+internal sealed interface SessionOutcome {
+
+    /** rc 0. The suspension resumes normally. */
+    data object Success : SessionOutcome
+
+    /** rc 255. The suspension is cancelled rather than failed — the user asked for this. */
+    data object Cancelled : SessionOutcome
+
+    /** Anything else, with the sentence the user is shown. */
+    data class Failed(val message: String) : SessionOutcome
+}
+
+/**
+ * Maps a return code onto the outcome, and builds the failure sentence when there is one.
+ *
+ * **The two message parts arrive as lambdas, deliberately.** `getAllLogsAsString` and
+ * `getFailStackTrace` are calls onto a native session, and only the failure arm needs either. Taking
+ * them by value would put both on the happy path of every successful conversion, which is a cost the
+ * shape this replaced did not have — the old code read them inside the `else` branch. That is the
+ * same reason [org.libremediaconverter.codec.AndroidDeviceCodecs.capabilitiesFrom] takes a
+ * `Sequence`: a seam should not change what runs when.
+ *
+ * A null [rc] is a real input rather than a defensive one — `getReturnCode()` is nullable, and a
+ * session killed before it reported anything has none. It is neither success nor cancellation, so
+ * it fails, and the sentence says `null` where the number would be.
+ */
+internal fun sessionOutcome(
+    rc: ReturnCode?,
+    prefix: String,
+    failStackTrace: () -> String?,
+    logTail: () -> String?,
+): SessionOutcome = when {
+    ReturnCode.isSuccess(rc) -> SessionOutcome.Success
+    ReturnCode.isCancel(rc) -> SessionOutcome.Cancelled
+    else -> SessionOutcome.Failed(
+        "$prefix failed (${rc?.value}): " + failStackTrace().orEmpty().ifBlank { logTail().orEmpty() },
+    )
+}

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

@@ -1,8 +1,8 @@
 package org.libremediaconverter
 
-import org.junit.Assert.assertEquals
+import kotlinx.coroutines.runBlocking
+import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertTrue
-import org.junit.Assert.fail
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -10,7 +10,6 @@ import org.libremediaconverter.convert.StagingSweep
 import org.robolectric.RobolectricTestRunner
 import org.robolectric.RuntimeEnvironment
 import java.io.File
-import java.util.concurrent.TimeUnit
 
 /**
  * That process start actually sweeps.
@@ -23,8 +22,19 @@ import java.util.concurrent.TimeUnit
  * output ever became a `Converted` state, a `reset()` whose delete was cancelled with the Activity.
  *
  * `onCreate()` is called again rather than a second Application being built: it is what the
- * framework calls at process start, the scope it launches on is already there, and the first test
- * below is what pins that the framework calls it on *this* class.
+ * framework calls at process start, and the scope it launches on is already there.
+ *
+ * **What this class stopped covering in #159, deliberately.** It used to open by asserting that
+ * `RuntimeEnvironment.getApplication()` is a [LibreMediaConverterApp] — that the manifest's
+ * `android:name` points here, so the sweep is code that actually runs. That assertion cannot exist
+ * on the JVM any more: `robolectric.properties` now names [TestLibreMediaConverterApp] for the
+ * whole suite, and an `application=` override replaces the manifest rather than being checked
+ * against it — `applicationInfo.className` reports the override too, measured. So the manifest is
+ * not merely unasserted here, it is unobservable from this source set, and a rewritten version of
+ * that test would have asserted the override against itself. **The manifest link is a device-only
+ * guarantee now**, and it was traded knowingly for the race that override fixes. The cast in
+ * [setUp] still fails if [TestLibreMediaConverterApp] stops extending the real class, which is a
+ * smaller claim than the one withdrawn.
  */
 @RunWith(RobolectricTestRunner::class)
 class AppStartSweepTest {
@@ -34,17 +44,35 @@ class AppStartSweepTest {
 
     @Before
     fun setUp() {
-        // The cast is an assertion in itself: Robolectric builds the Application named in the
-        // merged manifest, so this fails if `android:name` ever stops pointing here -- in which
-        // case the sweep below would be perfectly correct code that never runs.
         app = RuntimeEnvironment.getApplication() as LibreMediaConverterApp
         stagingDir = File(app.cacheDir, "conversions").apply { mkdirs() }
         stagingDir.listFiles()?.forEach { it.delete() }
     }
 
+    /**
+     * The property the whole substitution exists for, asserted directly rather than waited on.
+     *
+     * #159 is not "the sweep is slow", it is "the sweep is still running while some later test
+     * reads the directory". [TestLibreMediaConverterApp] answers that by finishing the sweep before
+     * `onCreate()` returns, and this is the only place that claim is checked -- every other test in
+     * the suite benefits from it silently and would go back to racing without saying why.
+     *
+     * Deterministic in the direction that matters: `Dispatchers.Unconfined` runs a `launch` whose
+     * body never suspends to completion inline, so this cannot flake green-to-red. Putting the test
+     * app back on `Dispatchers.IO` makes it a race that the assertion loses essentially every time,
+     * which is what a six-run suite comparison could not show -- at the rate #159 was observed at,
+     * a clean six-run arm is a coin flip.
+     */
     @Test
-    fun `the application the manifest starts is the one that sweeps`() {
-        assertEquals(LibreMediaConverterApp::class.java, RuntimeEnvironment.getApplication().javaClass)
+    fun `the sweep is finished before onCreate returns`() {
+        app.onCreate()
+
+        val sweep = app.startupSweep
+        assertNotNull("onCreate() started no sweep", sweep)
+        assertTrue(
+            "the JVM suite's sweep outlived onCreate(), so it is in flight during test bodies again",
+            sweep?.isCompleted == true,
+        )
     }
 
     @Test
@@ -64,35 +92,23 @@ class AppStartSweepTest {
 
         app.onCreate()
 
-        awaitGone(abandoned)
+        // Joined rather than polled. `onCreate` publishes the sweep it started, so this waits for
+        // that exact sweep -- where a timed poll could not tell "swept" from "not started yet", and
+        // answered the second case by failing after ten seconds.
+        val sweep = app.startupSweep
+        assertNotNull("onCreate() started no sweep to wait for", sweep)
+        runBlocking { sweep?.join() }
+
+        assertTrue("process start left ${abandoned.name} in staging; nothing swept it", !abandoned.exists())
         // The other half, and the one that says the sweep is a sweep rather than a
         // `clearStaging()`: the directory is shared by the convert tab, the join tab and
         // ConcatEngine's list file, so deleting everything could take a file from a running job.
         assertTrue("a file written moments ago belongs to a live job", live.exists())
     }
 
-    /**
-     * Waits for [file] to be deleted.
-     *
-     * The sweep runs on `Dispatchers.IO`, deliberately: it lists a directory and stats every entry
-     * on the path that decides how long the launcher icon stays unresponsive. So there is nothing
-     * to join, and the wait is a bounded poll — long enough for a directory listing, short enough
-     * that a sweep which never happens fails rather than hangs.
-     */
-    private fun awaitGone(file: File) {
-        val deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(AWAIT_TIMEOUT_SECONDS)
-        while (System.nanoTime() < deadline) {
-            if (!file.exists()) return
-            Thread.sleep(POLL_INTERVAL_MS)
-        }
-        fail("process start left ${file.name} in staging; nothing swept it")
-    }
-
     private fun stagedFile(name: String): File = File(stagingDir, name).apply { writeBytes(ByteArray(4096)) }
 
     private companion object {
         const val ONE_MINUTE_MS = 60L * 1000
-        const val AWAIT_TIMEOUT_SECONDS = 10L
-        const val POLL_INTERVAL_MS = 5L
     }
 }

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

@@ -0,0 +1,28 @@
+package org.libremediaconverter
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+
+/**
+ * The [LibreMediaConverterApp] the JVM suite runs, differing from it in exactly one thing: the
+ * startup sweep runs inline on the thread that builds the Application instead of on
+ * `Dispatchers.Unconfined`.
+ *
+ * **This is #159.** Robolectric builds an `Application` per test class that asks for one, and each
+ * one launches a sweep over the shared `<cacheDir>/conversions/`. Nothing joins them, so a test
+ * asserting about a staged file is racing however many sweeps the classes before it left in
+ * flight — `OutputPublisherStagingTest` being the one that lost, at roughly one local run in six
+ * once wave 4 added ten more Robolectric classes. Making the sweep finish before `onCreate()`
+ * returns removes the race for every test at once rather than asking each to opt in; 27 of the
+ * suite's 58 Robolectric classes touch that directory, so opting in was not a real option.
+ *
+ * `Dispatchers.Unconfined` is what makes it inline: `sweepStaging()` is a plain function, so an
+ * `Unconfined` `launch` runs it to completion before returning. The `SupervisorJob` is kept so this
+ * differs from production in the dispatcher alone — a sweep that throws is logged and swallowed
+ * here exactly as it is there, rather than taking Application construction down with it and failing
+ * every test in the class for an unrelated reason.
+ */
+class TestLibreMediaConverterApp : LibreMediaConverterApp() {
+    override val sweepScope: CoroutineScope = CoroutineScope(SupervisorJob() + Dispatchers.Unconfined)
+}

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/OutputPublisherStagingTest.kt

@@ -122,24 +122,25 @@ class OutputPublisherStagingTest {
 
     /**
      * Makes `cacheDir/conversions` a regular file, which is the whole precondition of the test
-     * above -- and does it in a loop, because a single delete-then-write loses a race that CI
-     * caught and this machine does not reproduce.
+     * above -- and does it in a loop, because a single delete-then-write once lost a race that CI
+     * caught and this machine did not reproduce.
      *
-     * `LibreMediaConverterApp.onCreate` ends with
-     * `appScope.launch { OutputPublisher(...).sweepStaging() }` on `Dispatchers.IO`, and
-     * `sweepStaging` reads `stagingDir`, whose getter calls `mkdirs()`. Robolectric instantiates
-     * the application for every test that asks for one, so that background `mkdirs()` is in flight
-     * across the whole suite, on a thread the paused main looper does not control. Between deleting
-     * this path and writing it there is a window where the path does not exist and that `mkdirs()`
-     * can win, which is `FileNotFoundException: ... (Is a directory)` out of `writeBytes` -- run
-     * 33069641674 on #149, once, against 468 tests that pass here.
+     * **That race is closed at the source as of #159, and the loop is kept anyway.**
+     * `LibreMediaConverterApp.onCreate` launched its staging sweep on `Dispatchers.IO`, and
+     * `sweepStaging` reads `stagingDir`, whose getter calls `mkdirs()`. Robolectric builds an
+     * application for every test class that asks for one, so that background `mkdirs()` was in
+     * flight across the whole suite, on a thread the paused main looper does not control. Between
+     * deleting this path and writing it there is a window where the path does not exist and that
+     * `mkdirs()` could win -- `FileNotFoundException: ... (Is a directory)` out of `writeBytes`,
+     * run 33069641674 on #149, once, against 468 tests that passed here. The JVM suite now runs
+     * `TestLibreMediaConverterApp`, whose sweep finishes before `onCreate()` returns, so nothing is
+     * sweeping while a test body runs.
      *
-     * Retrying closes it rather than narrowing it, because the race is not symmetric: `mkdirs()`
-     * fails on an existing regular file, so the invariant only has to survive being *established*.
-     * Once a write lands, nothing in the suite can turn this back into a directory.
-     *
-     * The wider problem -- application-scope IO work racing every Robolectric test that shares
-     * `cacheDir` -- is #159, and is deliberately not fixed here.
+     * The loop stays because it is what would catch that substitution being undone. Without it the
+     * regression returns as this one class failing rarely on CI -- the exact shape that took #159
+     * from a single run on #149 to a wave-4 flake before anyone chased it. Retrying closes the
+     * window rather than narrowing it, because the race is not symmetric: `mkdirs()` fails on an
+     * existing regular file, so the invariant only has to survive being *established*.
      */
     private fun stagingPathAsRegularFile(): File {
         val stagingPath = File(cacheDir, "conversions")

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/ffmpeg/SessionOutcomeTest.kt

@@ -0,0 +1,127 @@
+package org.libremediaconverter.ffmpeg
+
+import com.arthenica.ffmpegkit.ReturnCode
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * What a finished FFmpegKit session means, for both engines at once.
+ *
+ * `FFmpegEngine` and `ConcatEngine` each carried their own copy of this `when`, and the copies had
+ * drifted: one preferred the fail stack trace and fell back to the log tail, the other only ever
+ * read the log tail. Neither was tested, because both live inside a callback handed to `FFmpegKit`,
+ * which does not run on the JVM — so nothing could see that the two disagreed.
+ *
+ * **JVM-safe, verified rather than assumed.** `javap` over the committed AAR's runtime jar shows
+ * `ReturnCode(int)` as a plain public constructor with `SUCCESS`/`CANCEL` int constants and pure
+ * static `isSuccess`/`isCancel`; its `<clinit>` is constant initialisation and loads no native
+ * library.
+ *
+ * The unification is #203's decision, so the tests pin it as one: a join failure now carries the
+ * stack trace a conversion failure always did, while the two prefixes stay distinct.
+ */
+class SessionOutcomeTest {
+
+    @Test
+    fun `a return code of zero is success`() {
+        assertEquals(SessionOutcome.Success, outcome(ReturnCode(ReturnCode.SUCCESS)))
+    }
+
+    /**
+     * Cancellation is a separate outcome from failure, and the distinction is the point: the engines
+     * resume the continuation *cancelled* rather than exceptionally, so a user who pressed Cancel
+     * does not get an error card.
+     */
+    @Test
+    fun `a return code of 255 is a cancellation, not a failure`() {
+        assertEquals(SessionOutcome.Cancelled, outcome(ReturnCode(ReturnCode.CANCEL)))
+    }
+
+    @Test
+    fun `any other return code fails, and the sentence carries the number`() {
+        val failed = outcome(ReturnCode(1), stackTrace = "boom") as SessionOutcome.Failed
+
+        assertTrue("the code belongs in the message, got: ${failed.message}", failed.message.contains("(1)"))
+    }
+
+    /**
+     * The half that was different between the two engines before #203, now the same in both.
+     */
+    @Test
+    fun `the stack trace is preferred over the log tail`() {
+        val failed = outcome(ReturnCode(1), stackTrace = "the real cause", logTail = "…noise…")
+            as SessionOutcome.Failed
+
+        assertTrue(failed.message.contains("the real cause"))
+        assertTrue("the log tail must not be appended as well", !failed.message.contains("noise"))
+    }
+
+    @Test
+    fun `a blank stack trace falls back to the log tail`() {
+        val blank = outcome(ReturnCode(1), stackTrace = "   ", logTail = "the last few lines") as SessionOutcome.Failed
+        val absent = outcome(ReturnCode(1), stackTrace = null, logTail = "the last few lines") as SessionOutcome.Failed
+
+        assertTrue(blank.message.contains("the last few lines"))
+        assertTrue("a null stack trace is a blank one", absent.message.contains("the last few lines"))
+    }
+
+    /**
+     * Both sources empty still has to produce a sentence. A message ending in a dangling colon is
+     * thin, but it is what the user gets when FFmpeg said nothing at all, and it must not be an
+     * exception on the way to the screen.
+     */
+    @Test
+    fun `a failure with nothing to say still names the code`() {
+        val failed = outcome(ReturnCode(1), stackTrace = null, logTail = null) as SessionOutcome.Failed
+
+        assertEquals("FFmpeg failed (1): ", failed.message)
+    }
+
+    /**
+     * `getReturnCode()` is nullable and a session killed before it reported anything has none.
+     * Neither success nor cancellation, so it fails — and the sentence says so rather than throwing.
+     */
+    @Test
+    fun `a session with no return code at all fails`() {
+        val failed = outcome(null, logTail = "whatever was logged") as SessionOutcome.Failed
+
+        assertTrue("got: ${failed.message}", failed.message.startsWith("FFmpeg failed (null): "))
+    }
+
+    /**
+     * Unifying the *strategy* must not unify the *sentence*: the two engines describe different
+     * jobs, and a join that reports "FFmpeg failed" is a worse message than the one it replaced.
+     */
+    @Test
+    fun `each engine keeps its own prefix`() {
+        val join = sessionOutcome(ReturnCode(1), "Joining", { "cause" }, { null }) as SessionOutcome.Failed
+
+        assertTrue(join.message.startsWith("Joining failed (1): "))
+    }
+
+    /**
+     * Neither message source is read unless the outcome is a failure.
+     *
+     * They are calls onto a native session, and reading them on the happy path is work every
+     * successful conversion would do for nothing — which the shape this replaced did not, since it
+     * read them inside the `else` branch. That is why the parameters are lambdas, and this is what
+     * would notice if they stopped being.
+     */
+    @Test
+    fun `a session that succeeded reads neither the stack trace nor the log`() {
+        var reads = 0
+        fun counted(): String? {
+            reads++
+            return null
+        }
+
+        sessionOutcome(ReturnCode(ReturnCode.SUCCESS), "FFmpeg", ::counted, ::counted)
+        sessionOutcome(ReturnCode(ReturnCode.CANCEL), "FFmpeg", ::counted, ::counted)
+
+        assertEquals("neither source may be touched unless the session failed", 0, reads)
+    }
+
+    private fun outcome(rc: ReturnCode?, stackTrace: String? = null, logTail: String? = null) =
+        sessionOutcome(rc, "FFmpeg", { stackTrace }, { logTail })
+}

app/src/test/resources/robolectric.properties

@@ -10,3 +10,9 @@
 # Set here rather than in a @Config on each class so a later Robolectric test does not have
 # to rediscover it. Remove it once Robolectric ships an android-all jar for 37.
 sdk=36
+
+# Every test gets TestLibreMediaConverterApp, whose only difference from the real one is that the
+# startup sweep runs inline rather than on Dispatchers.IO. Set suite-wide because the race it fixes
+# (#159) is suite-wide: any class that builds an Application leaves a sweep of the shared staging
+# directory in flight for whatever runs next. TestLibreMediaConverterApp explains the choice.
+application=org.libremediaconverter.TestLibreMediaConverterApp

docs/e2e-read-findings.md

@@ -0,0 +1,327 @@
+# E2E-read findings
+
+**Status:** six findings, none fixed, none urgent — **plus one confirmed vacuous test, which is a
+ticket rather than an entry here** (see [Not covered here](#not-covered-here)). `E1`–`E6` came from
+the 2026-09-05 read of the instrumented suite. Every entry here is a *test-suite* observation —
+something a new test would not fix, because the test already exists and the problem is what it
+claims rather than what it runs.
+**Scope:** what reading all 60 instrumented tests turned up that writing a 61st would not fix.
+**Last verified:** `main` at `4b02294`, 2026-09-05. **60 `@Test` methods in 12 classes**, three
+carrying `@FailsOnEmulatorApi37`, gating API 37 leg 57.
+
+## Why this document exists, and why it is separate from the other two
+
+`docs/coverage-read-findings.md` (`F1`–`F10`) came from reading a **JaCoCo report**, and JaCoCo
+measures `testDebugUnitTest` only. So four waves of coverage work have been shaped by a number that
+**cannot see `app/src/androidTest` at all**. The instrumented suite has never had the equivalent
+read: nothing has asked what those 60 tests actually pin, only that they are green.
+
+That is the gap this read is in. It is a **triage, not a test push** — the same shape as wave 4's
+read, which "moved no number at all, and that is its result".
+
+`docs/defect-audit.md` (`D1`–`D16`) is the record of things *wrong at runtime*. Nothing here is
+wrong at runtime. These are tests whose names, KDoc or reputation overstate what they execute.
+
+Entry ids are `E1`–`E6` so they cannot be confused with `F1`–`F10` or `D1`–`D16`.
+
+## How to read the confidence labels
+
+Same vocabulary as the other two documents, deliberately:
+
+- **Confirmed by inspection** — the control flow is fully readable and the finding follows from it.
+- **Confirmed by measurement** — observed in a CI artifact, with the run id recorded.
+- **No action** — recorded because it looks like a finding and is not.
+
+## The method, and the one filter that found everything
+
+A coverage number is useless here by construction, so the read used a different question, applied
+to every one of the 60 tests:
+
+> **If the behaviour this test is named for stopped working, would it go red?**
+
+Three answers, and only the third is a gap:
+
+- **yes** — the test bites. Most of the suite.
+- **no, and that is deliberate and written down** — `RealMediaBenchmark` asserts nothing on purpose
+  (E2); `transcodesH264ToH265AndReportsProgress` declines to assert progress for a stated reason
+  (E3). These are entries here, not tickets.
+- **no, and nothing says so** — the gap. One test, and it is the most important one in the suite.
+
+**The reusable part is the second filter**, because "does it assert something?" would have cleared
+the vacuous test — it asserts two things. What it does not do is *reach the code it names*:
+
+> **Does the test's own premise hold on the machine that runs it?**
+
+`HardwareFallbackTest` asserts `SUCCEEDED` and a non-empty output, and both are true of a
+conversion that never went near the path it exists to prove (**#223**). See
+[Not covered here](#not-covered-here); it is filed rather than recorded here because a test fixes it.
+
+---
+
+## E1 — `RemuxTest`'s class KDoc argues for engine assertions three of its tests do not make, and they are right not to
+
+**Severity: low · Confirmed by inspection · the KDoc is what is wrong, not the tests**
+
+```
+app/src/androidTest/java/org/libremediaconverter/convert/RemuxTest.kt:31-42
+```
+
+The class KDoc is headed **"Why these assert the engine, not just the file"** and makes a specific
+argument:
+
+> A remux routed to FFmpeg produces a perfectly correct file — `-c copy` moves the same samples
+> into the same container. So an output-only assertion passes whether the hardware transmux path
+> ran or never executed at all […] which makes "silently always FFmpeg" the most likely way for
+> this feature to regress.
+
+Five of its seven tests run a conversion. **Three assert no engine at all:**
+
+| test | output container | asserts engine? |
+|---|---|---|
+| `mkvToMp4RemuxesOnHardware` | MP4 | **yes** — `MEDIA3` |
+| `mp4ToMkvRemuxesOnFFmpeg` | MKV | **yes** — `FFMPEG` |
+| `webmToMkvKeepsVp9WithoutReencoding` | MKV | no |
+| `audioOnlySourceRemuxesIntoMka` | MKV (`.mka`) | no |
+| `mp4ToMpegTsAndAviProduceTheirOwnContainers` | MPEG-TS, then AVI | **TS only**; the AVI half does not |
+
+### Why this is not a gap
+
+`ConversionRouter.MEDIA3_CONTAINERS = setOf(Container.MP4)` (`ConversionRouter.kt:37`), and every
+one of the three produces MKV or AVI. **They can only ever be FFmpeg**, so the regression the KDoc
+names — "silently always FFmpeg" — is not a thing that can happen to them. The two tests where the
+hardware path is genuinely at risk are exactly the two that assert it.
+
+An engine assertion on the other three would be near-tautological given today's router. It would
+catch one thing: somebody adding MKV or AVI to `MEDIA3_CONTAINERS` without a muxer to match — which
+is what `Media3MuxersTest` is for, on the JVM, where it does not need a device.
+
+### Why it is recorded rather than dropped
+
+**This was the strongest-looking candidate of the whole read and it dissolved on tracing**, which
+is the same shape as `F5` in the coverage document (filed as a test gap, and only stopped being one
+when someone went looking for its callers). Recorded so the next read does not re-file it.
+
+**The fix is one line of KDoc**, not three tests: the class asserts the engine *where the engine is
+in doubt*, which is a better rule than the one it currently states.
+
+---
+
+## E2 — three of the 60 instrumented tests assert nothing, and two of them never run
+
+**Severity: n/a · No action — deliberate, documented, and load-bearing as documentation**
+
+```
+app/src/androidTest/java/org/libremediaconverter/bench/RealMediaBenchmark.kt:25-53
+```
+
+`reportDeviceEncoderCapabilities` logs and asserts nothing. `hardwareVersusSoftwareOnRealVideo` and
+`av1InputRoutesAccordingToDeviceDecodeSupport` are `assumeTrue`-guarded on media that is **not
+committed** and must be staged by hand into the app's internal `filesDir`, so they skip in every
+automated run — they are the "2 skipped" every green leg reports, and `docs/local-emulator.md:305`
+says so.
+
+The class KDoc is unambiguous: *"This is a benchmark, not part of the automated suite […] Not a
+correctness test — the assertions are deliberately loose."*
+
+**No action.** Recorded for one reason: **the suite's headline number is 60, and three of those 60
+are not tests.** Any future statement of the form "60 instrumented tests cover X" is off by three,
+and two of the three have never executed on CI at all.
+
+**It is the opposite of E-nothing, though** — `reportDeviceEncoderCapabilities` runs on every leg
+and logs `BENCH can-encode:`, and **that log line is what confirmed the vacuous test this read
+found** (**#223**). An assertion-free test that prints the machine's capabilities turned out to be
+the only oracle in the suite. See [Not covered here](#not-covered-here).
+
+---
+
+## E3 — `transcodesH264ToH265AndReportsProgress` does not assert that progress was reported
+
+**Severity: low · No action on the test; the name is the inaccurate part**
+
+```
+app/src/androidTest/java/org/libremediaconverter/convert/Media3EngineTest.kt:73, :90-93
+```
+
+```kotlin
+// Deliberately NOT asserting that progress fired. Polling is on a 250 ms tick,
+// and a 3 s 320x240 clip can finish inside one tick on fast hardware, which
+// would make the assertion fail intermittently for no real defect.
+seen.forEach { assertTrue("progress out of range: $it", it in 0..100) }
+```
+
+`seen` is empty-safe: `forEach` on an empty list asserts nothing, so replacing `onProgress` with a
+no-op reddens nothing here. The reasoning is sound and the alternative really is a flaky test.
+
+**No action on the body.** The name says `AndReportsProgress` and the body says it does not check
+that, which is the `probeForConcat` shape from `CLAUDE.md` — *a passing test with a wrong
+explanation is its own failure mode* — in its mildest form, since here the KDoc immediately corrects
+the name.
+
+**Contrast the FFmpeg side, which is a real gap and is filed as #229**: `FFmpegEngine`'s percentage
+arithmetic is executed by every FFmpeg test and observed by none, because every call site omits
+`onProgress` entirely. Media3's is unasserted; FFmpeg's is unobserved. Only the second is a ticket.
+
+---
+
+## E4 — the marker's KDoc says removing it grows the gating leg by two; three tests carry it
+
+**Severity: low · Confirmed by inspection · one line**
+
+```
+app/src/androidTest/java/org/libremediaconverter/FailsOnEmulatorApi37.kt:20
+```
+
+> Delete the annotation from the tests, and the advisory job goes empty and the gating one grows by
+> **two**.
+
+Three tests carry it — `Media3EngineTest:72`, `Media3EngineTest:135`, `SafPickerRoundTripTest:320` —
+and `FAILS_ON_EMULATOR_API37_BASELINE = 3` eleven lines further down the same file, where the count
+is machine-checked by `.github/scripts/e2e-report-shape.sh`.
+
+The third marker was added when the SAF rotation test was excluded; the sentence was not updated
+with it. **Everything that is checked is consistent at three**; only the prose says two, which is
+exactly why it drifted — and a good argument for the baseline const being a const.
+
+---
+
+## E5 — `coverage-read-findings.md`'s F7 calls covered code uncovered
+
+**Severity: low · Confirmed by inspection · half of F7 is stale**
+
+F7 says `probeWithExtractor`'s catch (`MediaProbe.kt:180-182`) is unreachable on Robolectric and
+"stays device-only", measured across four URI shapes. **The unreachability claim is correct and
+stands.** The implication readers take from it — that nothing exercises it — does not:
+
+```
+app/src/androidTest/java/org/libremediaconverter/convert/RemuxTest.kt:111
+```
+
+`probeDistinguishesAudioFromImagesFromRubbish` feeds it a file of random bytes and asserts
+`InputKind.UNPARSEABLE`, on a device, on every gating leg.
+
+**"Device-only" holds; "uncovered" does not** — and the difference matters, because F7 is one of the
+six entries that document calls "no action", on the grounds that a test would not help. A test
+already exists. The entry should say so.
+
+**This is the failure mode the split between the two documents was meant to prevent**, and it caught
+this repo out: a JaCoCo-derived document cannot see `androidTest`, so it will keep re-deriving
+"uncovered" for anything the instrumented suite covers. That is a structural reason for this
+document to exist, not a one-off correction.
+
+---
+
+## E6 — the suite's one device-capability assertion derives its expectation from the call it is testing
+
+**Severity: low · Confirmed by inspection · no independent oracle exists**
+
+```
+app/src/androidTest/java/org/libremediaconverter/work/ConversionWorkerTest.kt:151-152
+```
+
+```kotlin
+val hasHardwareHevc = AndroidDeviceCodecs.get().canEncode(VideoCodec.H265)
+```
+
+and then the expectation is `if (hasHardwareHevc) MEDIA3 else FFMPEG`. The test asks
+`AndroidDeviceCodecs` what to expect and then checks that the router agreed with
+`AndroidDeviceCodecs`. **If the whole enumeration returned empty, this would still pass** — and
+empty is precisely what the `runCatching` fallback returns (the reason `#194` was worth cutting;
+it logs "assuming permissive" while making `canEncode` answer *no* for everything).
+
+Its KDoc defends the choice, and the defence is good:
+
+> Asserting MEDIA3 unconditionally tests the test machine, not the router.
+
+That is true, and there is no third source of truth on a device: `MediaCodecList` is what
+`AndroidDeviceCodecs` reads, so any oracle built from it is the same oracle.
+
+**No action, but read it with #223.** It is the same missing oracle that makes the
+vacuous-test fix a judgement call rather than a one-liner — you cannot assert "this device has
+hardware HEVC" from inside the suite without asking the class under test. The honest options are a
+visible skip or a red test, and that decision is the ticket's.
+
+---
+
+## Summary
+
+| ID | Finding | Severity | Evidence | Action |
+|---|---|---|---|---|
+| E1 | `RemuxTest`'s KDoc claims engine assertions three of its tests correctly omit | low | confirmed by inspection; traced through `MEDIA3_CONTAINERS` | **one line of KDoc** — the tests are right |
+| E2 | Three of the 60 instrumented tests assert nothing; two never run | n/a | confirmed by inspection; `docs/local-emulator.md:305` | **no action** — deliberate; but 60 ≠ 60 |
+| E3 | `…AndReportsProgress` does not assert progress fired | low | confirmed by inspection; reason inline | **no action** — the name overstates, the KDoc corrects it |
+| E4 | The API 37 marker's KDoc says "two"; three tests carry it | low | confirmed by inspection; baseline const says 3 | **fix the sentence** |
+| E5 | `coverage-read-findings.md` F7's "uncovered" half is stale | low | confirmed by inspection; `RemuxTest.kt:111` drives it | **amend F7** — "device-only" stands, "uncovered" does not |
+| E6 | The device-capability assertion asks the class under test what to expect | low | confirmed by inspection; no third oracle exists on a device | **no action** — read with **#223** |
+
+**Five of the six are prose, not code**, and that is the shape of this read. The instrumented suite
+is in good condition: 57 of its 60 tests bite, the fixtures are committed with their generation
+recipes, and the one class that asserts nothing says so in its first line. What this read found is
+that **the suite's self-description has drifted from the suite** in five small places and one large
+one.
+
+**The large one is not in this table**, because a test fixes it: **#223**.
+
+## Not covered here
+
+**The vacuous test.** `HardwareFallbackTest.aFileMedia3CannotDecodeStillConvertsViaFfmpeg` passes on
+every CI leg without ever entering the fallback it exists to prove. It is **#223**, not an entry
+here, because a test fixes it — and it is the reason this read happened rather than an aside from it.
+
+Measured, not inferred, on run **`34004304566`** (all legs green), from each leg's own
+`e2e-diagnostics-api*` logcat:
+
+```
+I/AndroidDeviceCodecs: Hardware video encoders: []
+I/RealMediaBenchmark: BENCH can-encode: COPY=true, H264=false, H265=false, VP9=false, VP8=false, AV1=false
+I/ConversionWorker: Routing sample_h264_444.mp4 -> OutputSpec(container=MP4, videoCodec=H265,
+                    audioCodec=AAC) via FFMPEG (NO_HARDWARE_ENCODER)
+```
+
+Identical on **API 33, 34, 35 and 37**. (API 36's logcat artifact on that run is truncated to 838 KB
+and carries no test output at all, so it is unread rather than different.) The job is routed
+**straight to FFmpeg before Media3 is attempted**, the `catch` in `runMedia3OrFallBack` is never
+entered, and the test's two assertions — `SUCCEEDED`, output non-empty — are true anyway. It ran in
+448 ms.
+
+**The repository already knew.** `ForcedFailureTest.hardwareFailureFallsBackToSoftware`, in the same
+package, pins `ConversionDependencies.deviceCodecs = { DeviceCodecs.PERMISSIVE }` and says why:
+
+> most emulators expose no hardware video encoder at all -- so the router would legitimately send
+> the job straight to FFmpeg and the hardware path would never be attempted. Without this the test
+> passes on a Pixel and fails on every emulator, which says nothing about the code under test.
+
+`ConversionWorkerTest.routesAFastMp4JobByDeviceCapability` records the same fact a third time. The
+knowledge is in two sibling files; `HardwareFallbackTest` is the one that walked into it — and
+because its assertions are about the *output* rather than the *path*, it passes where
+`ForcedFailureTest` would have failed. **That asymmetry is why nobody noticed.**
+
+**State it precisely.** The fallback *wiring* is covered on every leg by `ForcedFailureTest`, with
+fakes. What has never run on any emulator is a fallback triggered by a **real** mid-export codec
+failure — which is the case `HardwareFallbackTest` exists for, and the only reason
+`sample_h264_444.mp4` is committed at all. That fixture, generated with x264 because Fedora's
+ffmpeg ships openh264 and cannot produce High 4:4:4, does nothing on any CI leg today.
+
+The fix is not one assertion. `KEY_ENGINE_USED` is `FFMPEG` **whether the fallback fired or the
+router went straight there** — asserting it changes nothing. The vacuity guard is two facts
+together: the router chose `MEDIA3` for this request on this device, *and* the worker reported
+`FFMPEG`. Whether to reach that with `assumeTrue` (a visible skip on emulators, and the "2 skipped"
+becomes 3) or with an assertion (red on emulators, announcing it cannot test what it claims) is a
+decision, not a detail — see **E6** for why no third option exists — and **#223** leaves it open.
+
+**The other e2e gaps this read found are tickets too**, and are not repeated here:
+
+| # | Gap |
+|---|---|
+| **#223** | `HardwareFallbackTest` never attempts the hardware path on any emulator leg |
+| **#224** | Cancelling a *running* native session, in any of the three engines |
+| **#225** | No `content://` input has reached a *successful* conversion — the ffkitsaf bridge |
+| **#226** | `OutputPublisher.publish` against a real `DocumentsProvider`, and the SAF premise it rests on |
+| **#227** | The notification's Cancel action has never been fired |
+| **#228** | `encodesFlacLosslessAudio` and `encodesOpus` pass on any non-empty file |
+| **#229** | FFmpeg's progress percentage is computed everywhere and asserted nowhere |
+| **#230** | *(spike)* whether a running conversion's process can be killed under instrumentation |
+
+**Nothing here was filed as a coverage delta.** Each names the mutation that has to go red, which is
+the acceptance criterion wave 4 established and which caught two vacuous tests in that wave before
+they shipped. #223 is the one that shows why the criterion matters: it has two passing assertions and
+still tests nothing.

docs/local-emulator.md

@@ -312,6 +312,18 @@ on sample media that is deliberately not committed. Its third test,
 `reportDeviceEncoderCapabilities`, has no such guard and runs. A level reporting 0 skipped
 would mean someone had staged sample files, not that something improved.
 
+**Since #223 there is a third, and it is the interesting one.**
+`HardwareFallbackTest.aFileMedia3CannotDecodeStillConvertsViaFfmpeg` is `assumeTrue`-guarded on
+`AndroidDeviceCodecs.get().canEncode(H265)`, which is false on every emulator image — so it now
+skips here and runs only on the Pixel. It used to *pass* on emulators without ever attempting the
+hardware path, which is worse. **Expect `skipped="3"` locally**, and note the guard is a property
+of the machine rather than of staged files: a level reporting 2 would mean an emulator image had
+gained a hardware HEVC encoder, which is worth knowing.
+
+That test's KDoc carries the measurement, including the part that decides it: forcing the route to
+Media3 anyway does *not* produce a fallback, because the goldfish decoder decodes the High 4:4:4
+fixture despite declaring `NoSupport` for its profile.
+
 ### What the sweep adds, and what it does not
 
 **The renderer rule held four more times.** No boot log contains the string