Problem

When switching _AndroidTypeMapImplementation between llvm-ir and trimmable without a clean build, stale legacy JCWs contaminate the trimmable APK.

What happens

1. Build with llvm-ir: GenerateJavaCallableWrappers writes JCWs to android/src/ with Runtime.register(typeName, klass, methods) calls.
2. Build with trimmable: GenerateTrimmableTypeMap emits JCWs that should only call Runtime.registerNatives(klass), then places them in android/src/.
3. JCWs with different CRC-based package names survive the overlay, so both old and new wrappers can coexist.
4. _FindJavaStubFiles globs all *.java from android/src/, including stale legacy JCWs.
5. Both sets get compiled into classes.dex.
6. At runtime, a stale legacy JCW can call Runtime.register(), triggering the reflection-based registration path that is incompatible with trimming.

Previously, the C++ side silently dropped Runtime.register() calls because registerJniNativesFn was nullptr for trimmable mode, which masked the bug.

Fix (three layers)

1. Write JCWs directly to _AndroidIntermediateJavaSourceDirectory

The trimmable generator now writes to _AndroidIntermediateJavaSourceDirectory (android/src/) directly instead of typemap/java/ + copy. This removes the extra overlay step where stale files could survive.

2. Add _AndroidTypeMapImplementation to the properties cache

Switching typemap implementations now triggers _CleanIntermediateIfNeeded, which clears stale intermediate artifacts including android/src/.

3. Always wire registerJniNativesFn

Instead of silently dropping Runtime.register() calls in C++, the function pointer is always set. If a stale JCW somehow still calls Runtime.register(), the call now flows through to C# where TrimmableTypeMapTypeManager.RegisterNativeMembers throws UnreachableException.

Tests

• Unit test (JcwJavaSourceGeneratorTests): verifies trimmable JCWs emit Runtime.registerNatives (klass) and never emit the legacy Runtime.register(" path.
• Build integration test (BuildTest.SwitchingTypeMapImplementationTriggersClean): verifies that switching _AndroidTypeMapImplementation between llvm-ir and trimmable triggers _CleanIntermediateIfNeeded, while a no-change rebuild skips it.

Files changed

• JNIEnvInit.cs — remove the if (!TrimmableTypeMap) guard on registerJniNativesFn
• Trimmable.targets — write JCWs to _AndroidIntermediateJavaSourceDirectory directly and remove the extra output/copy step
• Common.targets — add _AndroidTypeMapImplementation to _PropertyCacheItems
• JcwJavaSourceGeneratorTests.cs — regression coverage for positive registerNatives and negative Runtime.register assertions
• BuildTest.cs — integration test for typemap implementation switching