LibreMediaConverter/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

LibreMediaConverter is an Android media converter (Kotlin, Jetpack Compose, Material 3) with two conversion engines: Media3 Transformer for the hardware path and FFmpeg for everything the platform cannot do. See @README.md for the architecture and @LICENSES/README.md for the split license — this file covers only what is not obvious from the code.

Build, test, lint

Everything is on Java 25 — daemon, CI, IDE, and the app's own bytecode. Four places say so and they must not drift apart:

Where	What sets it
Gradle daemon	gradle/gradle-daemon-jvm.properties → toolchainVersion=25
CI	java-version: '25' in both workflows
IDE	.idea/misc.xml
App bytecode	compileOptions in app/build.gradle.kts

Do not pick a JDK for the daemon — the repo does. gradle-daemon-jvm.properties carries foojay download URLs per platform, so Gradle provisions and runs the daemon on Java 25 regardless of what JAVA_HOME says (that only sets the launcher — ./gradlew --version prints both). Change it with ./gradlew updateDaemonJvm --jvm-version=NN, never by hand.

Reaching 25 in the bytecode row took a deliberate build change. AGP 9's built-in Kotlin compiles with the KGP it bundles — 2.2.10 for AGP 9.3.1 — and that caps jvmTarget at 24. The root build.gradle.kts puts KGP (and the lockstep Compose compiler plugin) on the buildscript classpath so AGP picks up 2.4.10 instead, which supports up to 26. That is why the module applies com.android.application and the Compose plugin by id() rather than from the catalog. Verified end to end, not assumed: compiled classes report major version 69, D8 dexes them, and R8 minifies them.

Consequences worth knowing before touching any of it:

• Raising kotlin requires a matching compose-compiler-gradle-plugin; they are one version.
• Still do not apply org.jetbrains.kotlin.android — incompatible with AGP 9's DSL.
• Java 24 is not an option even though Kotlin allows it: Adoptium dropped the EOL non-LTS, so there is no installable temurin-24. 25 is LTS and in the repo.

The Gradle wrapper does not float and cannot: distributionUrl names one archive and distributionSha256Sum is that file's checksum. Bump it with ./gradlew wrapper --gradle-version X --gradle-distribution-sha256-sum <sha> so the two stay consistent.

./gradlew :app:assembleDebug          # build debug APK
./gradlew :app:testDebugUnitTest      # JVM unit tests
./gradlew :app:ktlintCheck            # formatting
./gradlew :app:ktlintFormat           # fix formatting in place
./gradlew :app:detekt                 # static analysis
./gradlew :app:lintDebug              # Android lint
./gradlew :app:jacocoTestReport       # coverage (XML+HTML under app/build/reports/jacoco/)
# single unit test:
./gradlew :app:testDebugUnitTest --tests "org.libremediaconverter.model.ConversionRouterTest"

CI's "Static analysis" gate is exactly ./gradlew :app:ktlintCheck :app:detekt :app:lintDebug --continue. Run it with --continue locally too: one round trip gives you all three lists instead of the first one that fails.

Before treating a change as done, run: assembleDebug + testDebugUnitTest + compileDebugAndroidTestKotlin + ktlintCheck + detekt + lintDebug. compileDebugAndroidTestKotlin matters more here than it looks — the instrumented suite cannot run on this machine (below), so without it an androidTest compile error is not discovered until CI. ktlint and detekt also cover the test/androidTest source sets that lintDebug skips.

Instrumented tests: where they actually run

This section said the opposite until 2026-08-24, and both of its claims had been false for two days. Read it as the current answer, and see the git history if you need the old one.

• Local emulators work, for API 33-36. tools/local-emulator/run-e2e.sh runs them on this host. The segfault that made this look impossible was not a broken machine: SwiftShader's Reactor JIT writes generated shader code onto the heap and executes it, Fedora's SELinux policy denies execheap, and qemu dies. Choosing a different renderer avoids it entirely — -gpu host, angle_indirect and swangle_indirect all boot, while auto, off, guest and swiftshader_indirect do not. docs/local-emulator.md has the evidence and the per-API renderer table.

• CI runs API 37, and it gates. The matrix is 33/34/35/36/37. Three of the 60 instrumented tests cannot pass on that image, for two unrelated reasons: two Media3 hardware transcodes fail inside the emulator's own c2.goldfish.h264.decoder, and one SAF test takes the framework down when it rotates the display. All three carry @FailsOnEmulatorApi37 and run in a separate continue-on-error job; the gating leg runs the other 57.

  That job is still called E2E API 37 Media3 hardware transcode (advisory), which no longer describes everything in it. The name is kept deliberately — it is not a required context and people have learned to look for it — so read the marker, not the name, for what it holds. It is red on every PR, by design: do not read it as your change breaking something, and do not read a green run as evidence those three tests pass. docs/api-37-emulator-crash.md has the measurements.

  That instruction is also why nobody looks, so the job now reports its own shape — expected, received, failed, and whether the run completed — to the job summary, and compares it against FAILS_ON_EMULATOR_API37_BASELINE, committed beside the marker. A deviation is a ::notice::; the job stays advisory and its conclusion is untouched. Add or remove a @FailsOnEmulatorApi37 and that number changes in the same diff, or the next run says so. A bare failure count would not have worked: the run is usually truncated by an INSTRUMENTATION_ABORTED, and the test XML is written anyway and says nothing about it — .github/scripts/e2e-report-shape.sh is where that is measured and explained.

  Every leg prints that table, advisory or not, and on the wedge path it also carries a wedged: row (#118). completed cleanly only ever meant "instrumentation was not aborted", which stays true of a leg the WEDGE_TIMEOUT killed 22 minutes in — so without that row the table read received: 59, completed cleanly: yes for a leg that had just died. The wedge is passed to the report as E2E_WEDGED_AFTER by e2e-run.sh, which is the only thing that can know it: a wedge is gradle never returning, so the log it left says nothing about it.

Still true, and the reason the advisory job is not simply deleted: API 37 needs a manual check on the Pixel 10 Pro XL before each release. Those three tests are the one thing CI cannot answer for.

On a device or emulator, build only the ABI it can execute:

./gradlew :app:connectedDebugAndroidTest -PabiFilters=x86_64

FFmpeg's native libraries dominate the APK, so shipping arm64 to an x86_64 emulator doubles the install for code that can never run — and on API 37 the full APK does not fit at all.

Conventions

• ktlint owns formatting, detekt owns static analysis. detekt's formatting ruleset is off, so the two can never disagree about the same line. Never hand-fix a formatting complaint — run ktlintFormat. Style is intellij_idea at 120 columns, set in .editorconfig.

• detekt config is config/detekt/detekt.yml, merged onto detekt's defaults (buildUponDefaultConfig = true), so it carries only the rules this codebase legitimately breaks — each with the reason written next to it. Relax a rule that way or fix the code; never a bare @Suppress. Do not invent config keys: unknown ones are rejected.

• 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.

  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 skips no-location classes by default, and nothing told it otherwise — so not one Robolectric test counted, and Robolectric is what exercises the framework edge here. The isIncludeNoLocationClasses block in app/build.gradle.kts is what fixes it; do not delete it as stray config, and re-run the numbers if you ever touch it. Same commit, same 335 tests: 29.7% -> 69.2% with that block alone.

  The old entry also explained the wrong thing. It said coverage fell as the suite grew from 11 test files to 43 because "the denominator outran the numerator" on framework-edge code "the JVM cannot reach". The JVM reaches that code fine. What actually happened is that the new tests were disproportionately Robolectric, so each one added denominator and no numerator — the measurement was punishing exactly the tests that were hardest to write.

  Two things still hold. A floor needs a baseline that has settled, and this one has not. It moved 39 points in a single build change on 2026-08-24; then another 16 as the #52 test push and the fixes it turned up landed — 69.2% -> 84.9% line, 53.2% -> 63.8% branch — while the denominator grew 2194 -> 2321, because that work added production code of its own; then again on 2026-08-27 as #132 and #133's ten children landed — 84.9% -> 87.1% line, 63.8% -> 69.1% branch, 454 -> 502 tests. Branch moved four times as far as line that last time, and that is the shape to expect from this kind of work rather than a surprise: those children targeted decision code — enum fallbacks, refusal arms, cursor shapes, a when over container rules — where one test chooses a branch the suite had never taken. Line coverage barely notices; branch coverage is the whole point.

  Then #153's five children on 2026-08-29 — 87.1% -> 88.9% line, 69.1% -> 75.4% branch, 502 -> 546 tests.

  That last branch figure moved for two reasons, and only one of them is new tests. The numerator rose 974 -> 1011; the denominator fell 1410 -> 1340. Both are the seam work. Pulling a when out of a lambda inside a collect deletes the coroutine state machine's synthesized branches around it, and what is left is a plain function whose branches a test can choose: ConversionViewModel$observe$1$1 went from carrying the whole mapping to 6 branches, while the extracted ConversionViewModelKt covers 41 of 42 and JoinViewModelKt 38 of 39. So a seam is worth more than the tests it enables — it also stops the measurement counting scaffolding.

  Be careful quoting a branch move on its own for that reason. A percentage that rises because the denominator shrank is not the same claim as one that rises because more branches are tested, and this entry has a history of explaining its own numbers wrongly.

  Then wave 3 (#167-#178) on 2026-09-02 — 88.9% -> 92.8% line, 75.4% -> 81.3% branch, 546 -> 584 tests, in ten PRs from #179 to #188.

  Its shape is different from the two before it, and the difference is the thing to carry forward. Waves 1 and 2 were finding uncovered code. By wave 3 there was not much of that left, so the gaps were sorted into two kinds before any test was written:

  • coverage gaps — the line never executes. Filtered to sites where JaCoCo reports mi > 0, a concrete instruction no test runs, which is what separates a real gap from a partial branch on a compound condition. That filter cut the candidate list roughly in half and was right to.
  • assertion gaps — JaCoCo is green and nothing checks the answer. MainActivity's rail and bottom bar were both executed by AppRootRestorationTest and transposing them passed the entire suite; so did swapping the two progress-notification strings, and swapping Content's two destinations. No coverage number would ever have found any of the three.

  So every ticket named the mutation that had to go red, and that was its acceptance criterion rather than a coverage delta. It caught two vacuous tests written in the same session, before either shipped:

  • a firstContainerHolding test asserting a refusal still offered something. True, and useless: the source container is a candidate in its own right, so the list stays non-empty whatever the fallback does. What it actually buys is the codec the user asked for.
  • a staged-delete test scanning for a "join-" prefix StagingNames.forJob does not produce — it names files <jobId>.<ext>, so the assertion was true of everything.

  It also corrected a third test that was not vacuous: probeForConcat's KDoc claimed to drive the catch arm, and rethrowing from that catch left it green. That is how the arm turned out to be unreachable — see the next paragraph. A passing test with a wrong explanation is its own failure mode.

  A green mutation is only evidence when the mutation is a real change, which is the mirror trap: one classify mutation stayed green because reordering two arms was semantically equivalent for every reachable input. A bad mutation and a weak test look identical in the output.

  Three things came back not as the ticket described them, which is a result rather than a shortfall:

  • ContainerCapabilities:282's exclude filter cannot drop anything. repair always changes a codec on the shared container — a codec it left alone is one validate would not have refused — and the one non-default exclude carries COPY while every candidate carries NONE. F4-shaped.
  • probeForConcat's catch arm is unreachable on this runtime. Robolectric's MediaExtractor never throws from setDataSource, measured across an unregistered content:// authority, a missing file://, a file of garbage bytes and an http:// URL — all four returned with trackCount = 0. It stays device-only.
  • JobSnapshots:31's missed arm was not the !isFile one the ticket named — that is already covered by the reclaimed fixture. It was path == null: a job carrying no output path at all. Read the report, not the ticket, when the two disagree.

  One item was included against the F4 rule rather than exempted by it, and the distinction is worth having written down since both live in the same function: ContainerCapabilities:94 (accepts(container, VideoCodec.NONE, mode)) is dead in production today — every caller guards NONE first — and was tested anyway, because its audio twin at :101 has had a test since #136 and the asymmetry was the argument. The COPY -> error(...) arms beside it stay exempt, because a second line of defence that can be provoked is not one.

  Denominators moved here too, in both directions and for two different reasons: 1340 -> 1342 branches from MediaProbe.merge, 2348 -> 2352 lines from the ConcatJoiner interface. Neither is new untested code.

  And re-measure before quoting: this entry was once written quoting 81.4%, measured four hours earlier, and was already three points stale by the time it was ready to merge.

• 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.

  Three things make that a real bar rather than a slogan here:

  • Unit-testable is broader than it looks. The pure-seam pattern — work/FailureOutcome.kt documents the reasoning — turns "needs a device" into "a pure function plus a thin edge". Robolectric is in the JVM source set, compose-ui-test-junit4 with it, so Compose screens are unit testable too. Reach for the seam before concluding something cannot be unit tested.
  • E2E is runnable locally, API 33-36, via tools/local-emulator/run-e2e.sh — see "Instrumented tests: where they actually run" above. That was believed impossible until the SELinux/renderer cause was found, and it is what makes the e2e half of this norm enforceable.
  • A test has to bite. Revert the line it covers, confirm it goes red, restore. A review of this codebase ran 46 mutations against a 257-test suite and 9 were vacuous — five of them passing the whole suite over a completely unguarded code path. Green is not evidence.

  Name what you did not cover and why. Genuine exemptions exist; implied coverage is the problem.

• kotlin.code.style=official. Gradle stays Kotlin DSL.

• A stacked PR does not merge with gh pr merge, and MERGED is not proof it reached main. Two separate traps, both measured on 2026-08-27 while landing #144-#151.

  gh pr merge uses the GraphQL mutation, which refuses a stacked PR outright: "This pull request is part of a stack and must be merged using the asynchronous merge REST API." So does PUT .../pulls/{n}/merge. The one that works is gh api -X PUT repos/OWNER/REPO/pulls/N/merge-async -f merge_method=merge, which returns a uuid to poll at .../merge-async/{uuid} until status is merged or failed.

  The second trap is worse, because nothing looks wrong. GitHub retargets a stacked PR's base to main when the PR below it merges, but asynchronously. Merge a stack faster than that settles — five PRs about thirty seconds apart, in the case that found this — and each one merges into its own base branch, which has itself already been merged and left behind. Every call returns status: merged and every one is true. gh pr list --state open comes back empty, every PR shows MERGED, and none of the content is on main.

  What caught it was a coverage re-measure reading two points lower than the same tree had measured an hour earlier; a fresh git pull changed nothing, which is what turned it into a question. git merge-base --is-ancestor <merge-sha> origin/main answers it in one line. Do that after merging a stack, or merge one at a time and re-read baseRefName between. #160 is what the recovery cost.

  The auto-retarget belongs to the stacking feature specifically. A PR opened with a plain gh pr create --base some-branch does not retarget when that branch merges — it is left pointing at a dead base and has to be moved by hand.

• File one-off issues with tools/github/file-issue.sh, not gh issue create. gh issue create does not touch the project board, so the issue exists, carries its labels, and is invisible in the Kanban — indistinguishable from never having been filed. Measured 2026-08-24: eight issues filed as a scripted batch all reached the board; one filed as a one-off minutes later did not. A batch carries the board step in its loop; one-offs are where it slips, which is what the script is for. It resolves the project and Status ids by name rather than caching them, and it reads the item back — a mutation returning 200 is not evidence the board shows what was asked for. Exit 3 means the issue was created but did not reach the board, and prints the number so it cannot be lost quietly.

  above-cut and backlog are labels from the 2026-08-22 triage pass — "worked autonomously overnight" and "held for manual review". They are not board columns. Status carries board state; do not put a cut label on a newly filed ticket.

• shellcheck runs in CI, inside the Static analysis job, over git ls-files '*.sh' so a new script is covered without editing the workflow. It runs at full severity, info included: the two findings that raises today are answered with targeted disable directives carrying their reason, exactly as config/detekt/detekt.yml carries only the rules this codebase legitimately breaks. Do not silence it with --severity=warning — that hides the next real finding too. It is pinned by image digest, and joins ktlint/detekt/JaCoCo in the "Dependency versions" rule above — for exactly the reason stated there, demonstrated the day it was added. The first cut used the runner's ambient shellcheck. That is 0.9.0, while the container used to check locally was 0.11.0, and the two disagree about how to report a trap handler: 0.11.0 says SC2329 once on the declaration, 0.9.0 says SC2317 on each of seven lines in the body. Same script, same directive, one green and one red. Directives that must survive both name both codes.

  Locally, use the same pin rather than whatever is installed: podman run --rm -v "$PWD:/mnt:z" docker.io/koalaman/shellcheck@sha256:61862eba... <files> (the digest is in status_check.yml; there is no shellcheck system package on this host).

  actionlint covers the half shellcheck cannot see — the inline run: blocks, where a good deal of this repo's bash lives. It runs shellcheck over each run: plus its own checks on expression syntax, needs: references, matrix keys and action inputs. It sits in the same job, pinned by digest for the reason above and one of its own: its documented installer is a curl | bash off a moving branch, which does not belong in a repo that pins every action by SHA. Locally: podman run --rm -v "$PWD:/repo:z" -w /repo docker.io/rhysd/actionlint@sha256:9d360886... -color.

Dependency versions

Libraries float on minor + patch (coreKtx = "1.+"). Three groups deliberately do not:

• agp, kotlin, ksp are version-locked to each other. AGP 9.3.1's POM declares kotlin-gradle-plugin 2.2.10, and that is what AGP's built-in Kotlin compiles with. Android lint will suggest Kotlin 2.4.10; taking it breaks the Compose compiler unless KGP is also forced onto the root buildscript classpath. Move all three together, by hand, or none.
• ktlint, detekt and JaCoCo are pinned. A new rule in a linter makes files nobody touched stop passing, so CI goes red on a PR whose diff cannot explain it. Upgrading them is its own commit: run the tool, read the new findings, fix or relax them.
• The FFmpeg AAR is a committed file, not a coordinate.

+ does not mean "newest stable" on its own — Gradle will happily resolve it to an alpha, and androidx routinely publishes alphas numbered above the current stable (at last check: lifecycle, navigation, work, datastore and annotation all did). The componentSelection block in app/build.gradle.kts rejects prereleases, which is the only reason 2.+ means 2.11.0 rather than 2.12.0-alpha01. Do not remove it. To try a prerelease, name the exact version in the catalog — that pins it, which is the right way round.

Because versions float, a build can change without a commit. ./gradlew :app:dependencies --configuration debugRuntimeClasspath shows what actually resolved.

Traps

• Do not apply org.jetbrains.kotlin.android. AGP 9 has built-in Kotlin; applying the legacy plugin fails the build. This is why libs.versions.toml pins kotlin to AGP's bundled KGP version rather than the newest Kotlin release — the Compose compiler plugin must match it.
• The FFmpeg AAR is committed under bin/, deliberately. It is not on any Maven repo (ffmpeg-kit was archived and delisted). Rebuilding per CI run made red builds ambiguous: broken code, or a cross-compile that hiccuped? bin/README.md has provenance and how to regenerate it.
• Anything touching Media3 carries @UnstableApi rather than swallowing the marker with @OptIn. Android lint's UnsafeOptInUsageError catches a missed one.
• Release builds ship both ABIs. -PabiFilters is a test-run override only; build.yml verifies the released APK carries every ABI and that all native libraries are 16 KB aligned.
• A JUnit Timeout — rule or @Test(timeout=) — cannot be used in the JVM suite. Both run the test body on a separate thread, and every Compose test here goes through Robolectric's paused main looper: UnsupportedOperationException: main looper can only be controlled from main thread, from ShadowPausedLooper under RobolectricIdlingStrategy.runUntilIdle. The identical tests pass with the timeout removed, so it is the mechanism, not the test. What bounds a hung 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.