Proposal: Frame-owned Android interactive back previews without changing native history #11557

Need

Native routers can receive Android 14+ back progress through AndroidX, but Frame exposes only the final goBack(). A router that previews the previous Page currently has to temporarily parent its retained Android view itself, competing with Frame/Fragment ownership during cancellation or recreation.

Audited Core 9.1.3 and upstream main 3224f1b: Frame maintains its own logical back stack and uses FragmentTransaction.replace without addToBackStack. Enabling FragmentManager predictive pop is therefore not a drop-in change. Related investigation: rafaelaugustos/vue-router-ns#62.

Proposed experimental boundary

A presentation-only Frame.beginBackPreview() session with update(progress, edge), cancel(), finish(): Promise<boolean> and dispose(). Frame owns cleanup on navigation, unload, detach and native disposal. finish() does not navigate: a router remains responsible for guards and the final goBack(). Unsupported platforms/content return undefined.

The prototype renders the previous Page into a bounded Android bitmap/ImageView instead of parenting the live Page. No Page activation or Fragment back-stack transaction occurs during the gesture. Surface/TextureView content, secure windows, custom/shared transitions and oversized snapshots decline the session. This trades capture time/memory and a static preview for simpler ownership; it is not proposed as a default replacement until the tradeoffs are accepted.

Local native tests already cover actual system gestures, cancellation, guarded completion, modal inner stacks, replace/clearHistory and interruption. Native weak-reference checks verify snapshot bitmap collection. Tests and comparison traces will accompany the PR.

Recreation prerequisite found during the prototype

A plain NativeScript Frame can attach its new Android view while the recreated Activity is still INITIALIZED. _onAttachedToWindow() returns early; when the Activity reaches CREATED and the Frame loads, there is no second native attach event. Frame's _attachedToWindow stays false and a subsequent Back remains queued.

The candidate resolves the owning Activity and rechecks an already-attached native view in onLoaded(). The same-process recreation tests pass with both the legacy and prototype previews on Android API 34/35/36, retaining Page identities/draft state and allowing Back afterward. This is a small prerequisite correction, not a migration to FragmentManager's back stack.

A standalone NativeScript reproduction and automated native tests will be included with the implementation. Existing apps keep their navigation behavior; the new preview remains opt-in.