fix: gallery 'Media or File' sheet dismisses before you can pick media

[janicduplessis]

Fixes TLON-6142

Summary

Opening a gallery post (Pictures channel → New → "Media or File") flashes the second sheet ("Media Library / Capture / Upload a File / Voice Memo") open and immediately closes it, so you can't get to the media picker. The chat composer's single-level + sheet is unaffected — this only bites the two-sheet handoff in AddGalleryPost.

Changes

Root cause is in the shared BottomSheetWrapper (native). A gorhom modal dismissal fires both onChange(-1) and onDismiss. handleSheetChanges handles onChange(-1) — it respects the isProgrammaticChange flag (skipping the callback for programmatic closes) and then resets the flag. handleModalDismiss then ran with the flag already consumed, so it could no longer tell a programmatic dismissal from a user one and reported the close upward a second time.

For the gallery handoff, that spurious onOpenChange(false) runs the parent's onClose, which resets route back to 'gallery' — canceling the setTimeout-driven transition to 'add-attachment'.

This is a latent bug that only recently detonated:

• Planted in fix: bottom sheet modals fail to reopen after being dismissed #6039 (fix: bottom sheet modals fail to reopen after being dismissed), which added handleModalDismiss as an onDismiss fallback without the isProgrammaticChange guard that handleSheetChanges uses. Harmless at first — the spurious close landed before the 300ms handoff (gallery → gallery → add-attachment, a no-op).
• Triggered by feat(mobile): use native portals via react-native-teleport #6072 (native portals via react-native-teleport), which slowed the modal close enough that the spurious close now lands after the handoff (gallery → add-attachment → gallery), clobbering it. Confirmed by bisect: the flow works on a pre-feat(mobile): use native portals via react-native-teleport #6072 build and breaks once feat(mobile): use native portals via react-native-teleport #6072 is in.

handleModalDismiss is only a fallback for the case where gorhom skips onChange(-1) (dismiss mid-open-animation), so it's now gated on whether onChange(-1) already ran for this dismissal.

How did I test?

iOS simulator, dev build, Pictures channel → New → Media or File:

• Before: second sheet opens then instantly dismisses; can't reach the picker.
• After: second sheet stays open → Media Library → system picker → pick → post goes live in the gallery.
• Verified user-initiated dismiss still works (backdrop tap and picking a photo both close the sheet correctly — no stuck-open regression).

Before/after screen recordings below.

Risks and impact

• Safe to rollback without consulting PR author? (Yes)
• Affects important code area:
  • Onboarding
  • State / providers
  • Message sync
  • Channel display
  • Notifications
  • Other: shared bottom-sheet primitive (all native ActionSheet / modal sheets)

This touches the shared BottomSheetWrapper used by every native modal sheet, so the blast radius is wide. The change only removes a redundant close signal — the real close is still driven by handleSheetChanges(-1), unchanged — so it can't prevent a sheet from closing; worst case is the opposite (a sheet that gorhom dismisses without firing onChange(-1) fails to notify the parent), which the retained !reachedClosedIndex fallback path still handles. Worth a quick sanity pass on a couple of other sheets (channel actions, message long-press) during review.

Rollback plan

Revert the PR — single-file change, no native/config/schema changes.

Screenshots / videos

Before

Screen.Recording.2026-07-09.at.11.17.59.AM.mov

After

Screen.Recording.2026-07-09.at.11.15.28.AM.mov

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[linear-code]

TLON-6142