docs: guide for single-arch Android APKs (shorebirdtech/shorebird#3402)

[AzazelSensei]

I added a short guide for building a single-arch Android APK with Shorebird.

shorebird release android --artifact apk --target-platform android-arm64 has to go before --. Gradle NDK ABI filters alone still make Shorebird look for every default architecture.

Also documented shorebird releases get-apks --no-universal so you get per-ABI APKs instead of only universal.apk.

shorebirdtech/shorebird#3402
Fixes #470

[AbhishekDoshi26]

Thanks for writing this up — the flag details (--target-platform values/default, --no-universal default, --split-per-abi being unsupported, the -- placement) all check out against the current CLI source.

One claim looks stale, though. In release.mdx:

Gradle NDK ABI filters (for example ndk.abiFilters) are not enough on their own. Shorebird still looks for every architecture in --target-platform (all three by default). If Gradle drops an ABI Shorebird was asked to upload, the release fails. Keep those filters in sync with --target-platform, or drop the Gradle filters and use the flag only.

This describes the pre-fix behavior. createAndroidReleaseArtifacts in code_push_client_wrapper.dart now explicitly skips a missing arch directory instead of failing:

// Track which arch paths AGP didn't produce, so we can surface them at
// the end if zero archs uploaded. AGP omits an arch directory whenever
// the project filters it out via `ndk.abiFilters`, `splits.abi`, or
// `jniLibs.excludes`. Iterating only over present files lets a filtered
// release succeed instead of crashing on the first missing arch
// (https://github.com/shorebirdtech/shorebird/issues/3388).

It only errors if zero architectures are found for upload. Same pattern in android_patcher.dart's createPatchArtifacts, referencing the same issue. That fix (#3388) landed and was closed 2026-05-03, before this PR.

So today: a Gradle-filtered ABI that's still in --target-platform doesn't fail the release — it's silently skipped and the release ships with only the ABIs that actually built. Might be worth documenting that instead (i.e. "use --target-platform to declare intent explicitly, since a mismatched Gradle filter won't be caught with an error").

[AbhishekDoshi26]

Small change, rest looks good. Thanks!

[AzazelSensei]

You're right — that was the old behavior, before #3388. I updated the Gradle filter note in release.mdx (and the matching FAQ line): a filtered ABI that's still in --target-platform is skipped, and the release ships with whatever actually built. --target-platform is how you declare intent; a mismatch no longer fails the release.

[AbhishekDoshi26]

LGTM — fixed a Prettier formatting issue on release.mdx.