feat: penultimateCellIndex support, scroll-on-navigation, keyboard scoping, scroll position methods

[christopherwxyz]

Summary

Rebased onto main (v0.6.0) and adopted the mainScrollViewID-based scroll reset from #48.

penultimateCellIndex support

calculateBlankSize now respects the penultimateCellIndex prop:

• Negative value (e.g. -1): opts out of blank padding entirely — no gap between the last cell and the footer
• Non-negative value: uses that index for the penultimate cell lookup instead of always using blankView.index - 1
• nil (default): preserves existing behavior

Scroll reset on navigation

When the view leaves the screen (didMoveToWindow with window == nil), didScrollToEndInitiallyForId is reset. When returning, handleDidReturnToScreen re-triggers scroll-to-end. This handles Fabric view recycling where mainScrollViewID doesn't change when revisiting the same conversation.

Keyboard notification scoping

Adds ownsKeyboardSession flag so stacked screens (e.g. thread pushed over chat) don't interfere with each other's scroll/inset state.

Scroll position methods

1. getFirstVisibleCellInfo() — returns the first visible cell's index, pixel offset, and near-end state
2. scrollToCellOffset(cellIndex, offsetInCell, animated?) — scrolls to a specific cell at a given pixel offset

Changes

• aix.nitro.ts: Added AixVisibleCellInfo interface and two new methods to AixMethods
• HybridAix.swift: penultimateCellIndex support in calculateBlankSize, didMoveToWindow lifecycle for scroll reset, getFirstVisibleCellInfo() + scrollToCellOffset(), keyboard scoping
• HybridAix.kt: Android stubs for new methods
• nitrogen/generated/: Regenerated via bun run codegen

Test plan

• Navigate to a DM chat → messages scroll to bottom, no gap above footer
• Swipe back, navigate to different DM → scroll resets via mainScrollViewID change
• Navigate away and back to the same conversation → scroll resets via didMoveToWindow
• Stacked screens (thread over chat) → keyboard only affects the top screen
• penultimateCellIndex={-1} → blank padding is 0, last message sits above composer

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Additional Suggestion:

Missing resetInitialScroll() override in Android HybridAix.kt causes Kotlin compilation failure.

[richardkunkli]

Hey, this PR looks good. I also fixed this issue in my open PR (#48). Our current solution is to reset that state based on the change of mainScrollViewId property.

[nandorojo]

what is this used for?

[christopherwxyz]

getFirstVisibleCellInfo is a hook that saves and restores scroll position when navigating between chats. It:

1. On navigate away: calls getFirstVisibleCellInfo() to snapshot which message is at the top of the viewport (cell index + pixel offset within that cell + whether near bottom)

2. On return: calls scrollToCellOffset() to restore to that exact position

Without these methods, switching between conversations would lose your scroll position. It's the counterpart to the mainScrollViewID scroll-reset — reset handles the "scroll to bottom for new conversation" case, while this handles "resume where you left off."

[nandorojo]

Like @richardkunkli said, we're migrating to an approach that resets scroll state when mainScrollViewId changes. This way, you can do:

<ScrollView nativeId={`chat=${chatId}`}

Would that satisfy what you did with resetInitialScroll @christopherwxyz?

[christopherwxyz]

@nandorojo Yes — rebased onto main and adopted the mainScrollViewID approach from #48. Dropped resetInitialScroll() and didMoveToWindow entirely. Our JS side now passes a dynamic nativeId keyed to the conversation ID, so scroll state resets automatically when switching chats.

Repurposed this PR to add two new methods we need for scroll position memory:

• getFirstVisibleCellInfo() — snapshots the first visible cell (index + pixel offset + near-end state) so we can save scroll position on navigate-away
• scrollToCellOffset() — restores to a saved position on navigate-back

Also kept the keyboard notification scoping fix (ownsKeyboardSession) which prevents stacked screens from interfering with each other's keyboard state.