fix: window syllabus grid rows and drop eager prefetch

[posthog-eu]

Summary

The Syllabus Repository (/syllabus) rendered the entire catalog in one pass — getAllSyllabi() returns every row and SyllabusGrid rendered each as a Next <Link prefetch>. On large catalogs that combines mass route prefetching with a heavy hydration/render pass that blocks the main thread, so taps on rows stay unresponsive for tens of seconds (surfacing as rage-clicks) before navigation finally happens. There were no thrown exceptions — this is a performance/UX problem.

This PR keeps the instant client-side search intact while cutting the main-thread work:

• Window the rendered rows — only 48 rows render initially, revealing more via an IntersectionObserver sentinel as the user scrolls. The window resets on search; filtering still runs over the full list.
• Drop eager per-row prefetch — prefetch={false} plus hover/focus router.prefetch, matching the existing pattern in course-search.tsx, so we no longer fire prefetches for the whole catalog on load.
• Memoize SyllabusRow so selection changes only re-render the affected rows.

Why

Two independent session recordings on the /syllabus browse flow showed repeated rage-clicks and dozens of rapid dead clicks on syllabus rows, with navigation only succeeding 20–90s later — a repeatable degradation of a core content-discovery flow.

Verification

tsc --noEmit passes on the changed file (remaining errors are pre-existing, repo-wide missing generated .svg/.json type declarations produced by next dev). A live before/after could not be reproduced in the sandbox — no PostgreSQL server binary and no build/OAuth setup available — so this was not exercised against a running instance; the change directly targets the two root causes identified from the session recordings.

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Created with PostHog Code from an inbox report.

spent a lot of water and tokens to review your slop

Greptile Summary

This PR reduces initial work in the syllabus catalog. The main changes are:

• Renders syllabus rows in batches as the user scrolls.
• Resets the visible window when the search query changes.
• Disables eager link prefetching and prefetches on hover or focus.
• Memoizes individual syllabus rows.
• Adds a fallback for browsers without IntersectionObserver.

Confidence Score: 5/5

This looks safe to merge.

The search window now resets before the updated results commit. Browsers without IntersectionObserver no longer crash or leave the catalog truncated.

No blocking issues remain in the changed code.

T-Rex Logs

What T-Rex did

• T-Rex loaded the SyllabusGrid UI and launched the Playwright harness against the synthetic component page.
• T-Rex captured the initial rendered UI image showing a 48-row bounded window.
• T-Rex ran the runtime harness and inspected logs, which recorded the successful 48-link render followed by environment failures.
• T-Rex documented the available artifacts (image, logs, and source files) to help reviewers inspect the proof conditions.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
app/components/syllabus/syllabus-grid.tsx	Adds windowed row rendering, search-window reset, on-demand route prefetching, row memoization, and an observer fallback.

_{Reviews (2): Last reviewed commit: "fix: reset syllabus window during render..." | Re-trigger Greptile}

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Project	Deployment	Actions	Updated (UTC)
examcooker-dev	Error		Jul 13, 2026 4:21pm