perf(web): defer pull request line stats until visible

[Adamulek123]

What Changed

Pull request line counts are now requested only as rows approach the viewport. A single list-owned observer groups newly visible rows into immutable per-environment batches, and completed batches stay cached without being resent as more rows appear.

Why

The list previously requested line stats for every loaded row, including off-screen priority groups. Those reads use expensive host search APIs and could issue work for hundreds of pull requests on a cold page. The bounded visibility batches preserve row rendering and cached counts while avoiding document-wide observation and ever-growing request keys.

UI Changes

No visual design change. Rows still render immediately and line counts appear when available; off-screen rows no longer trigger speculative host reads.

Validation

• vp run --filter @t3tools/web typecheck
• git diff --check origin/main...t3code/pr-visible-line-stats

Checklist

• This PR is small and focused
• I explained what changed and why
• No visual UI change requires before/after screenshots
• No animation or interaction change requires a video

Generated with GPT-5.6 in the Codex harness.

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Note

Low Risk
Client-side performance optimization only; existing stats query and merge behavior are preserved with no auth or data-model changes.

Overview
Pull request diff line counts are no longer requested for every loaded row up front. The list now uses a shared IntersectionObserver (480px root margin) so stats are fetched only as rows approach the viewport.

PullRequestRow accepts optional statsKey and statsRef; the row button carries data-pull-request-stats-key and registers with the observer. On first intersection, the row is unobserved and deduplicated per filterKey, then appended as an immutable per-environment batch to statsTargetState instead of rebuilding targets from all groups on every change.

Cached counts still merge via statsByRow / usePullRequestListStats; UI behavior is unchanged—rows render immediately and counts fill in when available.

^{Reviewed by Cursor Bugbot for commit 1d318ee. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Defer pull request line stats queries until rows are visible in the viewport

• Previously, diff stats were fetched eagerly for all displayed pull request rows at once.
• Now, a shared IntersectionObserver (with rootMargin: 480px) in _chat.pull-requests.tsx triggers stats fetches only as rows approach the viewport, batching requests per environment.
• PullRequestRow accepts new statsKey and statsRef props to expose the button element for observation and key-based lookup.
• Duplicate requests within the same filter key are suppressed via a requestedStatsKeys ref; rows are unobserved after first intersection.
• Behavioral Change: stats queries now fire incrementally as the user scrolls rather than all at once on render.

^{Macroscope summarized 1d318ee.}

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[macroscopeapp]

Approvability

Verdict: Approved 1d318ee

Performance optimization that defers pull request line stats fetching until rows are visible using IntersectionObserver. The change is self-contained with no behavioral changes - same data is fetched and displayed, just more efficiently.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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