Desktop JVM and build footguns

24 traps mined from a production Kotlin and Compose Multiplatform app, one short file each under

references/

. Every file gives the working pattern, the Traps (the specific ways it fails in practice, and why), and a Verifying it section with commands to run against the user's own tree.

How to use this index. Match the code about to be written, or the symptom being chased, against the entries below: each names its topic and the symptom that should send you to it. Read every file that plausibly applies with the Read tool before proposing code or a fix; each is under 150 lines. Where a Verifying command names the source project's paths, substitute the equivalent paths in the user's tree.

Cross-references. A backticked trap name inside a file that is not listed here lives in a sibling area skill: glob

../*/references/<name>.md

to open it.

Native code on the desktop JVM

```
jna-native-binding-traps
```
— Hand-writing a JVM binding for a C library with JNA (Java Native Access) — the open-flags option that means something else on Windows, structs read by raw offset, callbacks the binding holds weakly, search paths registered too late, and proving which file was actually opened. Reach for it when a binding works on every developer machine and fails on a clean one, or when the very first symbol lookup fails with "the specified module could not be found" while the library is sitting right there.
```
native-artifact-for-embedding
```
— Producing a native shared library a JVM app can actually load and ship — why a prebuilt portable bundle usually is not a loadable library at all, building on the oldest base system you support, run-path choice, which libraries to deliberately leave out of the bundle, and gating the build on a load-and-initialize smoke test. Reach for it when the bundled native works on every developer machine and fails on a clean one, or when you discover the app has been quietly using a system-wide copy instead of yours.
```
bundled-native-soname-conflict
```
— A native library you bundle with a desktop app drags its own copy of a general-purpose base library along, that copy claims the shared-object name for the whole process the moment your native loads, and an unrelated platform API then fails with a missing-symbol message naming a third library. Use when a feature that opens links or system dialogs works on your machine but silently does nothing on users' machines, when a platform API reports itself unsupported at runtime, when deciding what a native bundle may contain, or when a merged fix for exactly this bug does not seem to have changed anything for users.
```
macos-codesign-sidecar-strip
```
— Strip the
```
._*
```
companion files that macOS archiving writes beside files carrying extended attributes, after unpacking anything into a macOS app bundle and before the bundle is signed, because the signer seals those companions as ordinary bundle members and the OS deletes them the first time the file manager touches the app. Use when a signed macOS app launches fine on the build machine but users are told it is damaged and can't be opened, or when signature verification reports a sealed resource missing.
```
jvm-desktop-memory-footprint
```
— Judge and reduce a desktop JVM application's memory honestly — read the heap-to-footprint ratio rather than the resident figure, run the one experiment that separates a leak from an allocator holding idle pages, and understand why per-thread allocator arenas make the footprint depend on the user's core count. Use when a desktop app settles near a gigabyte or keeps climbing over a long session, when users on big machines report far worse memory than you can reproduce, or before tuning any allocator or garbage-collector flag.
```
embed-media-engine-desktop
```
— Embedding a native C media engine in a JVM desktop app — one handle per media item, a dedicated event-pump thread, pinning the output driver and creating the render context in the right order, confining every property write to the thread that also releases handles, feature-detecting optional engine options, and formatting numbers the way the engine parses them. Reach for it when the app stops while setting a property, when the engine opens a window of its own, or when a value the app clearly sets is silently ignored.
```
merge-split-av-streams-desktop
```
— Playing a separate audio-only stream and video-only stream as ONE source on JVM desktop through the media engine's edit-list URL form — the desktop counterpart of a merging media source — including length-prefixed quoting of stream URLs and why a merged two-URL item must not be prepared in the middle of a crossfade. Reach for it when desktop video plays back completely silent with nothing in the log, when a stream URL is truncated at the first semicolon, or when fading into a video track cuts the outgoing song short.
```
compose-desktop-video-no-swingpanel
```
— Rendering video frames from a native media engine in Compose Desktop without embedding a heavyweight AWT panel — publish finished frames as immutable snapshots on a StateFlow and draw them with a plain Image, convert off the UI thread, match the engine's pixel byte order, and let the engine decide the fit. Reach for it when embedded video sits on top of everything regardless of z-order, lags a frame behind while scrolling, goes black on one screen the moment a second screen shows the player, comes out with red and blue swapped, or shows black bars that no content-scale can remove.
```
desktop-system-media-integration
```
— Wire a desktop app into each OS's system now-playing and transport surface behind one facade, so a failed native initialisation disables the integration and never takes playback down. Covers initialising on the platform's main thread inside a packaged app, reaching an OS media framework through the JVM's native-access layer, holding strong references to callbacks handed to the OS, and confining the integration to its own thread. Use when media keys or the system now-playing panel work under a plain Gradle run but not in the packaged app, when only the app name renders instead of the track title, or when transport callbacks stop arriving after a while.
```
upstream-lib-bug-workaround-template
```
— The shape a workaround should take when the bug is in a library you cannot patch — trace the mechanism as far as you actually got, name the tradeoffs you accepted, leave an escape hatch so a failure degrades instead of going silent, write the explicit condition for removing it, and record why your usage pattern exposes a bug the library's own users never hit. Use when you are about to pin a setting, avoid a code path or add a defensive branch because of someone else's bug, or when reviewing a workaround whose comment does not say when it may be deleted.
```
macos-lsenvironment-path-pin
```
— Declaring a Launch Services environment dictionary (
```
LSEnvironment
```
) in a packaged macOS app's property list pins the process
```
PATH
```
to the four bare system directories, so every external process the app spawns loses everything installed elsewhere. Use before adding any environment variable to a macOS app bundle, when a helper the app shells out to reports "command not found" only for installed users, or when a feature that works from a terminal launch silently does nothing from the Dock.

Packaging, signing, CI and build

```
conveyor-desktop-packaging
```
— Packaging a JVM desktop app with a config-driven packager whose HOCON config silently ignores unknown keys — which keys bind at the app level versus a per-OS section versus a nested group, command-line key overrides, pinning the packaging JDK, and the environment block that quietly pins PATH. Reach for it when a key you wrote is having no effect on the built installer and nothing in the build log complains.
```
config-fails-open-verify-artifact
```
— Verifying a config-driven feature against the generated artifact instead of against the config, for formats that fail open and ignore unknown keys — the two-build A/B diff, the artifact fingerprint to grep for, and the CI assertion that keeps it from regressing. Reach for it when a config key looks correct, the build is green, and the feature it configures has simply never been observed working.
```
desktop-deep-link-plumbing
```
— Wiring a custom URL scheme end to end on a JVM desktop app — per-OS registration, the argument filter at startup, single-instance forwarding, and delivering a callback's token to app state. Reach for it when clicking a link or returning from a browser redirect merely brings the app to the front and the flow it was supposed to complete just sits there.
```
r8-proguard-desktop-survival
```
— Running a bytecode shrinker over a JVM desktop app — which optimization families must stay off and why, why obfuscation breaks the rendering and reflection layers, the keep-rule families a native-binding plus coroutines plus HTTP-client app needs, and how to feed the shrunk jars to the packager. Reach for it when the release build starts with a verification error, renders a see-through or blank surface, or fails only in the packaged installer while the development run is fine.
```
gradle-config-resolved-too-early
```
— Diagnosing Gradle failures of the form "cannot mutate a configuration after its child configuration was resolved" — why the message names the configuration you touched rather than the plugin that resolved it, how to bisect plugins against a minimal working template, and which fixes are documented dead ends. Reach for it when adding a perfectly ordinary dependency line makes the build refuse to configure, and rewriting that line every possible way changes nothing.
```
transitive-version-pinning
```
— Handling a transitive dependency whose strict version constraint overrides the version you chose, dragging a shared lower-level library up or down for the whole build — how to find who pinned what, when to force a version back versus align everything with the pin, and how to document a pin so nobody upgrades it back into the breakage. Reach for it when adding one unrelated library produces a missing-method failure at runtime, inside a rendering pass, in a component you did not touch.
```
reproducible-native-bundling-two-tasks
```
— Ship prebuilt native libraries to a multiplatform desktop build by splitting bundling into two Gradle tasks with different homes — a dev-machine task that builds the slices, packs tarballs and prints their digests, and a CI task that only downloads and verifies against digests pinned in the build file; reach for it when CI needs a native toolchain it should not have, when a native bump quietly ships the previous binaries, or when the packaged installer launches with the native missing entirely.
```
windows-vm-detection-post-wmic
```
— Detect that a desktop app is running inside a virtual machine on Windows after the classic command-line management query tool was removed in Windows 11 — query the management layer through PowerShell, probe both the manufacturer and the model field, and pick the fail direction deliberately; reach for it when a transparent or undecorated window renders nothing on a VM while the process keeps running, or when a detection probe that worked for years suddenly reports empty on every modern host.
```
windows-msix-offline-installer
```
— Ship a self-signed MSIX (the modern Windows application package format) that end users can actually install without a hosted update site — bundle an install script plus the signing certificate beside the package, script the trust-then-sideload steps, and keep the signing key stable across releases; reach for it when double-clicking the packager's output fails, when its wrapper installer dies fetching a URL that returns 404, or when a new build refuses to install over the previous one.
```
arm64-native-gap-audit
```
— Audit every native dependency for a slice on a CPU architecture before promising that target in a multiplatform desktop build — one missing native takes the whole target down at first use rather than at build time, so make the audit a repeatable command over the resolved artifacts and re-run it on every dependency bump; reach for it when deciding whether to add an ARM64 target, or when a build that packaged and installed cleanly dies the first time it touches the database, the renderer or the media layer.
```
ci-flaky-timing-luck
```
— Find and fix CI steps that only ever passed by timing luck — an asynchronous detach of a same-name mounted volume colliding with the next iteration's mount, and a downloader that quietly saves an error page as the artifact; reach for it when a step that ran green for months starts failing after a runner image update, or when a job succeeds and something minutes later fails on a corrupt or empty file it was handed.
```
github-actions-multiplatform-release
```
— Structure a GitHub Actions release pipeline for a multiplatform desktop app so one Linux runner cross-builds every platform's artifacts and a second, tiny macOS job does only the one step that genuinely requires macOS — with artifact handoff between them and no compilation on the costly runner; reach for it when your release workflow runs three OS jobs that each rebuild the world, or when macOS users hit a hard block dialog on an app the pipeline signed correctly.
```
buildkonfig-secrets-flavors
```
— Wire build-time configuration into a Kotlin Multiplatform app with BuildKonfig — secrets read from an untracked local properties file and injected as generated constants, with the no-secrets branch getting empty strings so the feature disables itself instead of failing the build, plus the task-dependency wiring newer Gradle demands for generated sources; reach for it when common code needs a compile-time constant, when an open-source build must not carry credentials, or when a build fails on an implicit dependency between a generated-source task and a consumer.

desktop-and-build-footguns

NPX Install

Tags

SKILL.md Content

Desktop JVM and build footguns

Native code on the desktop JVM

Packaging, signing, CI and build