fix(zoom): auto-placed zoom regions follow the cursor for their whole span

[EtienneLescot]

Summary

• Auto zoom regions (created by the magic-wand cursor-dwell suggestion pass, source: "auto") were built with focusMode left undefined unless the separate, global "Auto Focus All" toggle was on.
• With focusMode not "auto", the zoom/pan render used the static dwell-centroid focus point captured when the region was suggested and never tracked the cursor for the rest of the region — matching the reported symptom of the zoom "jumping to the cursor's position at the start and then staying fixed."
• The cursor-follow interpolation logic (zoomRegionUtils.ts / cursorFollowUtils.ts) already existed and worked correctly when focusMode: "auto" — it just wasn't being applied by default to auto-suggested regions.
• Fix: buildAutoZoomRegions in src/components/video-editor/VideoEditor.tsx now always sets focusMode: "auto" for regions with source: "auto", independent of the "Auto Focus All" toggle (which still only controls the default for manually-drawn zoom regions — unchanged).

Root cause

src/components/video-editor/VideoEditor.tsx — buildAutoZoomRegions() set focusMode: autoFocusAll ? "auto" : undefined for every auto-suggested region. Since autoFocusAll defaults to false, freshly auto-placed zoom regions got focusMode: undefined, which getResolvedFocus() in src/components/video-editor/videoPlayback/zoomRegionUtils.ts treats as "manual" (static focus point), so the pan never sampled cursor telemetry across the region's time range.

Test plan

• Added src/components/video-editor/videoPlayback/zoomRegionUtils.test.ts: regression test asserting an auto-zoom region's resolved focus tracks moving cursor telemetry across its span, and that a manual-focus-mode region stays pinned to its static focus (manual regions unaffected).
• npx tsc --noEmit — no new errors (2 pre-existing unrelated errors for optional @xenova/transformers / onnxruntime-web deps).
• npm run lint (biome check on changed files) — clean.
• npm run test — all 52 test files / 409 tests pass.
• Live app smoke test (record → auto-zoom → playback) was not performed in this session due to the setup cost of driving real screen capture from a worktree; verification here is unit-test only. A manual smoke test recording a clip with cursor movement, letting the magic wand auto-place a zoom region, and confirming the pan follows the cursor during playback is recommended before merge.

Fixes #72

Summary by CodeRabbit

• Bug Fixes

  • Auto-placed zoom regions now continuously follow the cursor throughout their duration.
  • Manual zoom regions continue to preserve their fixed focus.
  • Improved zoom behavior consistency when automatic focus settings are enabled or disabled.

• Tests

  • Added regression coverage for cursor-following behavior in automatic zoom regions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 2177e8cc-1baf-47a5-b203-3a5fe52a02ec

📥 Commits

Reviewing files that changed from the base of the PR and between d5966ed and e92e3e3.

📒 Files selected for processing (2)

• src/components/video-editor/VideoEditor.tsx
• src/components/video-editor/videoPlayback/zoomRegionUtils.test.ts

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📝 Walkthrough

Walkthrough

Auto-generated zoom regions now always use automatic cursor-following focus, independent of the global Auto Focus All setting. Regression tests cover automatic cursor tracking and static manual focus behavior.

Changes

Auto zoom focus behavior

Layer / File(s)	Summary
Auto zoom region generation src/components/video-editor/VideoEditor.tsx	Auto-generated regions now set focusMode: "auto" unconditionally, retain source: "auto", and remove autoFocusAll from memoization dependencies. Comments document the behavior.
Focus behavior regression tests src/components/video-editor/videoPlayback/zoomRegionUtils.test.ts	Tests verify automatic regions follow cursor telemetry over time while manual regions remain pinned to their static focus.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: siddharthvaddem

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the bug, root cause, and testing, but it omits several required template sections like type, release impact, desktop impact, and screenshots.	Add the missing template sections, especially type of change, release and desktop impact, screenshots/video, and complete testing details.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: auto-placed zoom regions now follow the cursor across their span.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/72-auto-zoom-follow-cursor

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