android: Cgo removal is blocked by the gomobile/x-mobile JVM bridge (tracking)

[changkun]

Tracking the Android conclusion from the merged design spec specs/mobile-remove-cgo.md (#123): Android cannot drop the Cgo / C-toolchain dependency under the current gomobile model. Filing so the rationale is discoverable and the investigation isn't repeated.

Why it's blocked

1. The backend needs golang.org/x/mobile/app.RunOnJVM → internal/mobileinit.RunOnJVM, implemented with C.lockJNI/C.unlockJNI/C.checkException — Cgo, pulled in transitively before our own clipboard_android.c.
2. gomobile Android apps build -buildmode=c-shared via the NDK; CGO_ENABLED=0 is not a supported flow. Empirically GOOS=android CGO_ENABLED=0 go build . fails on the x/mobile/app import.

Considered and rejected

purego-over-JNI (purego supports Android dlopen): would replace clipboard_android.c but not remove the toolchain requirement — x/mobile/app stays Cgo and the NDK c-shared build stays. Churn + unsafe risk with zero movement toward the goal.

Revisit when

The JVM/Context lifecycle (current JNIEnv + app Context) can be obtained without a Cgo x/mobile dependency. Until then: no source change; Android keeps Cgo + NDK, and clipboard_nocgo.go keeps its !android exclusion. See spec §7.

[changkun]

Closing as not planned (wontfix). The investigation is complete and its conclusion is now captured in the merged design spec specs/mobile-remove-cgo.md (§5, §7): Android cannot drop the Cgo / C-toolchain dependency under the current gomobile model.

In short:

1. The backend needs golang.org/x/mobile/app.RunOnJVM → internal/mobileinit.RunOnJVM, implemented with C.lockJNI/C.unlockJNI/C.checkException — Cgo, pulled in transitively before our own clipboard_android.c.
2. gomobile Android apps build -buildmode=c-shared via the NDK; CGO_ENABLED=0 is not a supported flow.

purego-over-JNI was considered and rejected (removes neither the x/mobile/app Cgo dependency nor the NDK requirement). No source change lands.

This mirrors the closure of the iOS tracking issue #125. Revisit when the JVM/Context lifecycle becomes obtainable without a Cgo x/mobile dependency — until then Android keeps Cgo + NDK, and clipboard_nocgo.go keeps its !android exclusion.