## Summary

`libapp.so` could be silently dropped from release APKs
and app bundles, surfacing as either:

- a runtime crash on launch — `VM snapshot invalid and could not be
inferred from
  settings` — for APKs, or
- a `Release app bundle failed to strip debug symbols from native
libraries`
  build failure for app bundles.

## Root cause

Regression from flutter#181275, which moved `libapp.so` from a jar dependency
onto a
Flutter Gradle Plugin source-set `jniLibs` directory. That delivery was
fragile
in two ways, both of which dropped `libapp.so` from the merged native
libraries
(while `libflutter.so`/`libdartjni.so`, delivered as AAR dependencies,
were
unaffected — which is why the failure looked asymmetric):

1. The source-set `jniLibs` `srcDir` was resolved eagerly
(`.get().asFile`) at
`:app` configuration time, while the copy task wrote lazily. When `:app`
was
   evaluated before its build directory had been redirected — a combined
`subprojects { … evaluationDependsOn(":app") }` block (the pre-flutter#91030
template
shape) together with a plugin whose Gradle subproject name sorts before
`:app` — the two disagreed on the build directory and the staged
`libapp.so`
   was never merged. (flutter#186810)
2. The copy task wrote into a directory nested inside the Flutter task's
own
output directory, creating overlapping task outputs that undermined
Gradle's
incremental checks — e.g. a flavored project where a prior single-ABI
build
(a `flutter run` on one device) left the other ABIs missing `libapp.so`.
   (flutter#187388)

## Fix

Stage `libapp.so` (and any bundled native assets) through a dedicated
`CopyFlutterJniLibsTask` whose output is registered on each variant via
AGP's
variant API:
[`variant.sources.jniLibs.addGeneratedSourceDirectory(...)`](https://developer.android.com/reference/tools/gradle-api/9.1/com/android/build/api/variant/SourceDirectories#addStaticSourceDirectory(kotlin.String)).
AGP then
owns the task dependency, resolves the output path lazily (correct
regardless of
project evaluation order or build-dir redirection), keeps it in its own
output
directory (no overlapping outputs), and strips/extracts debug symbols
from it
like any other native library. This restores the robustness of the
original
jar-based inclusion while keeping `libapp.so` strippable.

## Tests

New integration test `gradle_libapp_so_packaging_test.dart` covering
both
triggers: the combined `subprojects` block + a plugin sorted before
`:app`, and
a flavored single-ABI build preceding a multi-ABI build.

Fixes flutter#186810
Fixes flutter#187388
Fixes flutter#187553