fix(mobile): improve font-size slider performance and prevent maximum update depth errors

[bbernag]

What Changed

• Keep drag progress entirely in Reanimated shared values while the finger is down.
• Commit the final snapped font size to mobile preferences once when the gesture finishes.
• Return cancelled gestures to the committed value without applying an update.
• Preserve immediate commits for taps and accessibility increment/decrement actions.

Why

The slider previously crossed to JavaScript and wrote mobile preferences for every intermediate pan value. Updating the base text size also reapplies app-wide typography variables, so rapid back-and-forth scrubbing could queue global renders, leave the slider replaying delayed values after release, and eventually trigger Maximum update depth exceeded.

With this change, only the slider thumb and fill move during a drag. The preview, value label, global typography, and persisted preference remain unchanged until release, when the final snapped value is committed once.

UI Changes

There is no visual redesign. The interaction now defers all font-size updates until the slider is released.

Before

Heavy scrubbing could repeatedly update global typography, lag behind the gesture, continue after release, and trigger the maximum update depth error.

Screen.Recording.2026-08-15.at.3.01.30.p.m.mp4

After

The thumb and fill track the gesture smoothly, and the selected font size is applied globally once on release.

Screen.Recording.2026-08-15.at.3.00.12.p.m.mp4

Validation

• Mobile tsc --noEmit
• Targeted vp lint --report-unused-disable-directives
• Targeted vp fmt --check
• git diff --check
• Android emulator held-drag check: value remained unchanged before release
• Android emulator release check: the final snapped value committed after UP
• Original font-size preference restored after runtime validation
• Rules review found no violations

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after videos for the interaction change

Built with GPT-5 using the Codex desktop harness.

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Note

Low Risk
Localized interaction change in settings appearance sliders; main risk is any consumer expecting continuous onChange during drag, which now only fires once on successful release (plus tap/a11y).

Overview
Pan drags on the appearance font-size slider no longer call onChange on every move. While dragging, only Reanimated progress updates so the thumb and fill track the finger without touching persisted preferences or global typography.

On pan end, a successful gesture snaps progress to the stepped value and calls commit once (with haptics). A cancelled/failed pan animates back to the current value and does not invoke onChange. Taps still commit immediately on end; accessibility increment/decrement is unchanged.

Gesture useMemo now depends on value so failed drags can reset to the latest committed size.

^{Reviewed by Cursor Bugbot for commit acc6aac. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix font size slider to commit changes only on gesture release

• onChange and haptics are no longer fired continuously during a pan drag; they fire once when the gesture successfully finalizes with the snapped value.
• If the pan gesture fails, the slider animates back to the current value without calling onChange.
• Tap gestures still commit once on tap end, and gesture memoization now updates when value changes.
• Behavioral Change: apps relying on continuous onChange callbacks during drag will now only receive a single callback on release.

^{Macroscope summarized acc6aac.}

Summary by CodeRabbit

• Bug Fixes
  • Improved font size slider behavior when dragging.
  • Cancelled gestures now restore the current setting, while completed gestures correctly snap to and save the selected value.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Team

Run ID: d68a30f6-a0f1-4bf5-ad10-3b5cdd197be3

📥 Commits

Reviewing files that changed from the base of the PR and between bc3dc26 and 47590e4.

📒 Files selected for processing (1)

• apps/mobile/src/features/settings/appearance/components/FontSizeSliderRow.tsx

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📝 Walkthrough

Walkthrough

The font size slider now distinguishes cancelled and successful pan gestures. Cancelled gestures restore the current value. Successful gestures snap and commit the value derived from animated progress.

Changes

Font size slider gesture handling

Layer / File(s)	Summary
Gesture finalization and commit handling apps/mobile/src/features/settings/appearance/components/FontSizeSliderRow.tsx	commit caches the latest value. Cancelled pans restore the current value. Successful pans derive a snapped value from progress.value. Gesture memoization includes value.

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

Merge Risk: ⚪ Minimal · up to 47590

The slider now commits font-size changes only after successful drag completion while cancelled drags restore the saved value. The supplied checks indicate the intended mobile behavior is ready to merge.

Suggested reviewers: juliusmarminge

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the mobile font-size slider fix and its performance and update-depth goals. It matches the main changes in the pull request.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It explains the behavior change, provides before-and-after interaction videos, and documents validation res…
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.

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• Create PR with unit tests

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[macroscopeapp]

Approvability

Verdict: Approved 5061496

Small, self-contained UX change that moves font size commit from continuous drag updates to only on slider release. Limited to a single mobile settings component with clear intent and low risk.

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