fix: Fixes auto-scroll releasing when transaction commits

[pan-kot]

Description

Fixes a bug when auto-scrolling would not stop after transaction commits. Logically, when the transaction is submitted or discarded, the auto-scroll handlers should be removed, which is supposed to prevent the scroll. However, this does not happen due to a rather complex lifecycle involved. Removing unneeded React state and making the event listeners added and removed only once per component mount/unmount fixes the problem.

Before:

Screen.Recording.2025-08-25.at.18.15.39.mov

After:

Screen.Recording.2025-08-25.at.18.16.07.mov

Rel: AWSUI-61150, similar to: #368

How has this been tested?

• New functional test for regression
• New unit tests to cover the auto-scroll util

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.40%. Comparing base (8ff00c0) to head (b9c9f45).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #367      +/-   ##
==========================================
+ Coverage   94.98%   95.40%   +0.41%     
==========================================
  Files          67       67              
  Lines        3250     3263      +13     
  Branches      692      703      +11     
==========================================
+ Hits         3087     3113      +26     
+ Misses        163      150      -13     

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[cansuaa]

Doesn't scrollIntoView already scroll? Why do we need this.scrollRepeat()?

If there is no activeElement in the document, where is this supposed to scroll?

[pan-kot]

The scrollRepeat repeatedly checks for the cursor position and if it is on edge - it will scroll automatically with small time increments.

The scheduleActiveElementScrollIntoView is an action which is called on-demand. To have no conflict with the repeated scroll, it reuses the same timeout reference. First, it clears the timeout which is normally set every 10ms by scroll repeat. Then, it performs its own scrolling after a delay. Finally, it has to restart the repeated auto-scroll, as otherwise it won't work anymore after scheduleActiveElementScrollIntoView() is called.

[cansuaa]

Does this go beyond the window and cause scrolling?

[pan-kot]

This goes to the bottom edge of the window, which is enough. The auto-scrolling activates when the cursor is within 50px from either top or bottom screen edge.