fix(android): declare gesture simultaneousness bidirectionally between content pan and scroll

[ronnymajani]

Motivation

On Android, the inner scrollable inside a BottomSheet cannot be scrolled when the sheet is first opened. Dragging vertically inside the scrollable does nothing — the content pan gesture cancels the native scroll on every touch. Curiously, focusing then blurring a TextInput inside the sheet "fixes" the problem for the remainder of that session, after which the scroll works normally.

Diagnostic instrumentation showed the symptom precisely: onScrollBeginDrag fires 4× in succession with zero onScroll events between them — i.e. RNGH keeps starting the scroll and immediately canceling it in favor of the pan.

Root cause

BottomSheetDraggableView creates the content pan gesture with:

gesture = gesture.simultaneousWithExternalGesture(simultaneousHandlers as never);

…where simultaneousHandlers is built from nativeGestureRef, refreshControlGestureRef, and any user-provided handlers. It does not include the inner scrollable's Gesture.Native().

Meanwhile, createBottomSheetScrollableComponent does declare the relation on the scroll side:

Gesture.Native()
  .simultaneousWithExternalGesture(draggableGesture)   // declares pan as simultaneous
  .shouldCancelWhenOutside(false)

So the simultaneousness is only declared on one side. RNGH on Android requires the declaration on both sides — on iOS the one-sided declaration appears to be enough, which is why this bug only manifests on Android.

The "focus then blur an input" workaround presumably forces RNGH to re-resolve its internal gesture tree, at which point the declarations end up coordinated.

What this PR does

Introduces a NativeScrollGestureContext that lets the inner scrollable register its Gesture.Native() back up to the outer BottomSheetDraggableView. The pan then includes that gesture in its simultaneousWithExternalGesture(...) array, completing the bidirectional declaration.

Three notable implementation choices, each captured in inline JSDoc on the changed files:

1. State, not ref

simultaneousWithExternalGesture resolves its argument at gesture-handler registration time. A ref whose .current is null at that moment results in no relation being established, and subsequent ref mutations are not picked up — RNGH does not lazily re-resolve.

A useState is therefore required: when the inner scrollable mounts and registers its gesture, the resulting state update re-renders the BottomSheet, recomputes the pan's useMemo, and re-attaches its GestureDetector with the relation now in place.

2. Setter is idempotent (first non-null wins)

Without a guard, the setter would loop:

set scroll → state update → pan re-creates → new pan flows into the scrollable via BottomSheetDraggableContext → scrollable's useMemo rebuilds scrollableGesture → effect re-fires with the new identity → set scroll → …

(Reproducible: yields a hard Maximum update depth exceeded after ~50 iterations.)

Once a non-null gesture is registered, subsequent non-null registrations are no-ops. The bidirectional relation only needs to be established once; further updates would only churn the gesture tree without changing semantics.

3. Registration effect has no deps-change cleanup; unmount cleanup lives in its own effect

For the same loop-avoidance reason: nulling the registration on every deps change would re-render the pan without the scroll, then re-register, then re-render the pan with the scroll, ad infinitum. The deps-change branch of the cleanup is dropped; a separate unmount-only effect (using a ref to capture the latest context) still clears the registration when the scrollable fully unmounts (e.g. when the sheet closes).

Files changed

File	Change
src/contexts/gesture.ts	Adds NativeScrollGestureContext with {nativeScrollGesture, setNativeScrollGesture}. JSDoc explains the why.
src/components/bottomSheet/BottomSheet.tsx	Provides the context with a useState-backed value and an idempotent setter.
src/components/bottomSheetDraggableView/BottomSheetDraggableView.tsx	Consumes the context and adds nativeScrollGesture to the pan's simultaneousHandlers.
src/components/bottomSheetScrollable/createBottomSheetScrollableComponent.tsx	Registers its scrollableGesture via the context on mount; clears on unmount.

No public API changes. No type changes. No behavior change for any platform/scenario where the scroll already worked.

Verification

• yarn typescript — clean
• yarn lint --error-on-warnings — clean on the four modified files (the pre-existing warning in src/hooks/useBoundingClientRect.ts is on master and untouched here)
• Manual test on a physical Android device with the example app and with my own production app: scroll inside the sheet now works on first open, no need for the focus/blur reset. iOS behavior unchanged.

Related

This bug is the underlying cause for several long-standing reports about scroll/pan conflicts in BottomSheet content on Android (notably the "scroll only works after focusing an input" pattern).

Happy to break this into smaller commits, adjust the comments, or rework the context shape if you'd prefer a different approach.