perf(mobile): render Home rows further ahead while scrolling

[AKolenda]

What Changed

Home's list renders rows up to 1,000 beyond the screen instead of 500 (drawDistance), as a named constant. Five lines, on top of #13702 (merged).

Why

With #13702, rows away from the viewport are cheap dormant frames, but the list still rebuilds recycled rows while a fling moves it, and on a busy JS thread that can fall behind: #13702 alone still showed a blank list in 1 of 5 runs. Rendering further ahead means a fling reaches rows that are already built.

Pixel 9, real account (57 rows on Home), release build installed in place, the same 10 fast flings per run, all runs in one session:

build	runs with blank frames	blank list time per run	janky frames	app memory (PSS)
main (2 runs)	2 of 2	2.1 s	2.9–3.3%	618–629 MiB
#13702 alone (5 runs)	1 of 5	0.31 s in that run, none in the others	1.9–2.4%	525–571 MiB
#13702 + draw distance 1,000 (2 runs)	0 of 2	none	—	550–567 MiB
#13702 + draw distance 2,000 (3 runs)	0 of 3	none	2.0–2.4%	585–622 MiB

1,000 instead of 2,000: at 2,000 the list keeps about 67 rows mounted, more than this account's 57, so those runs measured a list with recycling effectively off. 1,000 still recycles on this account, had no blank frames, and costs no memory over #13702 alone.

Also checked on physical iOS and Android devices with a preview build of this change: scrolling feels smooth. A very fast fling that reverses direction can still show a brief blank. At high speed LegendList moves its whole render buffer ahead of the scroll direction, so a larger draw distance would not fix that case either.

UI Changes

No visual change to a row. Same flings, #13702 alone (its worst run) on the left, with a longer draw distance on the right (MP4; recorded at 2,000):

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Draw distance tuned from 2,000 to 1,000 and rebased onto main by Claude Code (Opus 5.5), after on-device testing by a maintainer.

Summary by CodeRabbit

• Performance
  • The Home screen now prepares more list content ahead of the visible area, which may help keep scrolling smooth.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a production mobile rendering and interaction architecture change, adding automatic swipe-row activation, touch tracking, an alternate dormant row path, and a larger render-ahead window across several files. Because it changes existing Home behavior through nontrivial stateful coordination rather than a small isolated tuning adjustment, it merits human review.

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📝 Walkthrough

Walkthrough

HomeScreen now sets LegendList’s draw distance to 1,000, increased from 500.

Changes

Home list draw distance

Layer / File(s)	Summary
Set the Home list draw distance apps/mobile/src/features/home/HomeScreen.tsx	HomeScreen defines a draw-distance constant of 1,000 and passes it to LegendList instead of 500.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: 🟡 Moderate · up to 463f9

Confirm the intended draw distance before merging: the current value differs from the one used for the reported no-blank-frame results.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 69ed8

The changes affect which Home rows are prepared ahead of scrolling and when their swipe gestures become active. The reviewed path does not add access to thread data or new action authority. Overall security coverage remains incomplete.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The identified exposure is local to Home list rendering and swipe availability; the supplied impact map identifies one changed mobile system and no changed dependency edges.

Trust Boundaries and Controls

• observed — The scroll gate disables swipe gestures during qualifying vertical drag and settling, while the activation store avoids swapping row frames during a list-started touch.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly describes the main change: increasing mobile Home list rendering distance to improve scrolling performance.
Description check	✅ Passed	The description is complete and focused. It explains the change, motivation, test results, memory trade-offs, UI impact, stacked PR dependency, and includes interaction evidence. The screenshot checkl…

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[AKolenda]

@juliusmarminge #13702 is critical to this PR. With it, Home rows that are off screen skip the swipe gesture and its hidden action buttons, so the phone has far less to build while you scroll. That alone removes most of the blanks (2.1 s → 0.31 s per run) and is what lets this PR render further ahead without using more memory. This PR already contains the code from #13702, so merging this PR merges #13702 too. If you would rather merge them one at a time, merge #13702 first.

[juliusmarminge]

I know. 13702 is ready to merge. Just tuning this one before merging as a pair

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Actionable comments posted: 1

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Inline comments:
In `@apps/mobile/src/features/home/HomeScreen.tsx`:
- Line 144: Update THREAD_LIST_V2_DRAW_DISTANCE to 2,000 so the value passed to
LegendList matches the intended draw distance.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 69ed86a and 463f95b.

📒 Files selected for processing (1)

• apps/mobile/src/features/home/HomeScreen.tsx

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