feat(ui): added enhancements to scroll momentum

[devr0306]

Summary

Made scroll momentum reset on direction change and truncated while flushing instead of in each scroll event.

Details

The new architecture in ScrollProvider.tsx moves away from simple "delta summing" to a more robust Absolute Floating-Point Synchronization model.

1. The "True" Position Tracker (floatValue)
   Instead of tracking how much the user moved (deltas), the provider now tracks the component's ideal fractional position.

   • This high-precision float represents where the list should be if the terminal had infinite resolution.
   • Because we store the absolute target rather than a sum of changes, rounding errors cannot accumulate over time, ensuring the scroll feels "anchored" to your finger or wheel.

2. Reality Checks (expectedScrollTop)
   To prevent the high-precision "ideal" state from drifting away from reality, we introduce an Ownership Check.

   • We store the last integer value we successfully applied to the UI (expectedScrollTop).
   • On every new scroll event, we compare this to the component's real current position.
   • If they differ: We know an external event (like a PageDown keypress, a layout shift, or a scrollbar drag) moved the list.
   • The Sync: The provider immediately discards its fractional momentum and "re-anchors" its math to the list's new real-world position. This prevents "teleporting" bugs where the list would jump back to a stale position.

3. Proactive Boundary Clamping
   The high-precision floatValue is now strictly clamped within the list's physical boundaries (0 to maxScroll) during every update.

   • This eliminates "momentum debt" at the edges.
   • Without this, if you scrolled "up" 10 times at the top of a file, the float would reach -10. You would then have to scroll "down" 10 full times before the list even started moving. Clamping ensures your very first reverse flick has immediate visual impact.

4. Direction-Aware Momentum
   The momentum engine is now direction-sensitive.

   • The acceleration multiplier (up to 3x) is only maintained as long as you continue scrolling in the same direction.
   • If you rapidly switch from "down" to "up" within the 50ms window, the system detects the direction flip and immediately resets the multiplier to 1.0x, providing much finer control when navigating precisely.

5. Consolidated Math (getClampedScrollTop)
   All logic relating to the relationship between scrollHeight, innerHeight, and the current position has been unified into a single helper. This ensures that the boundary checks used to allow a scroll event are identical to the logic used to clamp the final rendered state.

Related Issues

Closes #24438

How to Validate

Have a long chat history in alternate buffer mode and scroll fast. Momentum should be smooth and reset on direction change.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refines the scroll momentum implementation within the UI context. By introducing direction tracking and adjusting how scroll deltas are processed during flushing, the changes ensure a smoother and more intuitive scrolling experience, particularly when reversing direction.

Highlights

• Scroll Momentum Logic: Updated the scroll momentum logic to reset when the scroll direction changes, ensuring more predictable behavior.
• Delta Handling: Modified the scroll flushing mechanism to truncate delta values and preserve fractional remainders, improving smoothness during accumulation.

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[github-actions]

Size Change: +1.78 kB (+0.01%)

Total Size: 34 MB

Filename	Size	Change
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./bundle/core-W7DS4R63.js	0 B	-45.1 kB (removed)	🏆
./bundle/devtoolsService-VR7WH6N7.js	0 B	-28.4 kB (removed)	🏆
./bundle/interactiveCli-PWYY3XZG.js	0 B	-1.63 MB (removed)	🏆
./bundle/oauth2-provider-AGQWXG4J.js	0 B	-9.16 kB (removed)	🏆
./bundle/chunk-CGESP654.js	14.8 MB	+14.8 MB (new file)	🆕
./bundle/chunk-KQNSTDAX.js	3.15 MB	+3.15 MB (new file)	🆕
./bundle/core-JHR4UTIC.js	45.1 kB	+45.1 kB (new file)	🆕
./bundle/devtoolsService-7L6VSZPF.js	28.4 kB	+28.4 kB (new file)	🆕
./bundle/interactiveCli-KQSIUGLI.js	1.63 MB	+1.63 MB (new file)	🆕
./bundle/oauth2-provider-5E57SQ6V.js	9.16 kB	+9.16 kB (new file)	🆕

ℹ️ View Unchanged

Filename	Size
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./bundle/devtools-36NN55EP.js	696 kB
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./bundle/sandbox-macos-permissive-open.sb	890 B
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[gemini-code-assist]

Code Review

This pull request improves scrolling smoothness and momentum logic within the ScrollProvider. Key changes include implementing fractional scroll accumulation by preserving remainders across flushes, ensuring scroll acceleration only triggers for consecutive scrolls in the same direction, and improving cleanup when unregistering scrollables. A test case was also updated to reflect the refined delta calculations. I have no feedback to provide as there were no review comments to evaluate.

[jacob314]