feat: RN TurboModule -- threading + Fabric integration, rebuilt (supersedes #46)

[DjDeveloperr]

What this is

Threading + Fabric integration for the RN TurboModule, rebuilt from scratch after the owner rejected #46's architecture (see DECISIONS.md/ARCHITECTURE.md). installWorkletRuntime puts the real NativeScript interop bridge on the worklets UI runtime, so a "worklet" hook calls UIKit directly with zero JSON/RPC round-trip. The UI runtime is main-queue-scheduled but not thread-affine — runOnUISync is banned, only async crossings allowed — so the UI/JS-thread deadlock is unconstructible rather than merely gated.

API shape

One call whose hook names ARE the Fabric ObjC lifecycle names; bodies are worklets:

export const Screen = defineNativeComponent<ScreenProps, ScreenEvents, ScreenInstance>({
  name: "NSScreen",
  props: { activityState: 2, stackPresentation: "push", title: "" },
  events: ["onAppear", "onDisappear", "onDismissed"],
  create(ctx) {
    "worklet";
    const vc = (globalThis as any).UIViewController.alloc().init();
    vc.view = ctx.view;
    ctx.instance.controller = vc;
  },
  updateProps(ctx, next) {
    "worklet";
    if (next.title) ctx.instance.controller.navigationItem.title = next.title;
  },
});

Proof + line counts

packages/react-native-screens/src/index.ts is a full UINavigationController native stack (push/pop/modal, header config, transitionCoordinator-gated reconciliation) in 458 lines, zero native code — vs. a 16,029-line NativeScriptScreenStack.tsx for the same surface in the rejected #46.

• Module (TS surface + native Fabric glue): 2,329 + 2,058 = 4,387 lines.
• Net diff vs refactor across both packages: 44 files, +3,366/-4,553.
• Whole-branch diff vs refactor: 55 files, +4,698/-4,561.
• feat: add React Native UIKit runtime primitives #46 for comparison: +16,263 insertions over 46 files.

What was deleted

The process-wide UIView/RCTViewComponentView method swizzle (NativeScriptUIView.mm), NativeScriptUIViewManager.mm, NativeScriptUIViewComponentView.{mm,h}, NativeScriptUIKitHost.h, installIdleAwareWorkletsFrameLoop, BatchOps.mm and its walkers, nativeCommitObservations/nativeHandleAuthority, the point-fix RPCs, and the old defineUIKitView/defineUIKitContainer/defineUIViewController surface with its registries. Grepped clean — nothing references any of it.

Known caveat

UIViewControllerTransitionCoordinator's completion block is declared solely on a protocol; the metadata resolver only walks the concrete class hierarchy, so that one call site needs interop.Block(fn, "v@?@") instead of a bare closure (see reconcileStack in the screens consumer). Class-declared completions (presentViewController:animated:completion:) already work with a bare closure. #71 fixes this at the runtime level; until it lands, protocol-declared completion params need interop.Block.

Supersedes #46.

[coderabbitai]

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