recorder: auto-scroll segment bar when a clip is added

[morepriyam]

Closes #167.

Stacked on #170 (same file); only the last commit is this PR's change.

Scroll-to-newest existed in f2a1e38 but was dropped in 400fc68 with the scroll-preservation work — since then a clip recorded or imported past the right edge of a full bar lands invisibly off-screen.

Change

Reinstated alongside the preservation logic as one direction-keyed effect — reorder never changes the segment count, so the branches are mutually exclusive by construction:

• Length increase (recording finalized or library import — both arrive through the same live query) in record mode → animated scrollToEnd, deferred to onContentSizeChange so the new thumb has laid out before the scroll fires
• Length decrease (delete) → the existing restore-offset behavior, untouched
• Gated on the cursor being absent — while previewing, playhead-follow owns the scroll, so the two mechanisms can't fight

Testing

• tsc --noEmit, ESLint, and the jest suite clean
• Verified on device: new recordings and library imports scroll the newest thumb into view on an overflowing bar; scroll position still preserved on delete; playhead-follow unaffected while previewing

[Copilot]

Pull request overview

This PR restores “scroll-to-newest” behavior for the recorder segment bar when a new clip is added, while preserving existing delete offset restoration and avoiding conflicts with playhead-follow during preview.

Changes:

• Track segment-count direction changes and schedule an animated scrollToEnd on length increases (new recording/import) when not previewing.
• Keep existing “restore previous offset” behavior for length decreases (delete).
• Defer the scroll-to-end until onContentSizeChange so the new thumbnail has measured before scrolling.

Suppressed comments (1)

src/features/recorder/segment-bar.tsx:172

• onContentSizeChange will execute scrollToEnd whenever stickToEnd is set, even if the user has entered preview mode since the segment was added (cursor now truthy). Also, if both restoreOffset and stickToEnd are set (e.g. batched updates), the current two independent if blocks will restore the offset and then immediately scroll to end, breaking the delete-preservation behavior. Guard the scroll-to-end by !cursor and make the two branches mutually exclusive, cancelling any pending stick-to-end when previewing.

              // Honor a pending scroll-to-newest now that the added thumb has been measured.
              if (stickToEnd.current) {
                stickToEnd.current = false;
                scrollRef.current?.scrollToEnd({ animated: true });
              }

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/features/recorder/segment-bar.tsx:108

• stickToEnd can remain set across a subsequent length DECREASE (delete) if a clip is removed before the pending scrollToEnd runs. In that case onContentSizeChange will restore the offset and then immediately scroll to end, defeating the delete-preservation behavior. Clear any pending stickToEnd when a decrease is detected so deletes can never trigger an unintended auto-scroll.

    if (cursor) stickToEnd.current = false;
    if (segments.length < prevCount.current) restoreOffset.current = scrollOffset.value;
    else if (segments.length > prevCount.current && !cursor) stickToEnd.current = true;
    prevCount.current = segments.length;

[SarkarShubhdeep]

Auto scroll to newly added clip works with no issues.