pagination fast scroll virtualization

Status: done

Objective:

• Fix fast-scroll stalls on /examples/pagination with strategy=virtualized.
• Keep the 1000-page stress document and 10-page table bounded during fast jumps.
• Prove the fix with browser interaction metrics, DOM budgets, focused Playwright coverage, typecheck, lint, and package release artifact.

Source:

• User report: fast scrolling in the virtualized pagination example breaks because rendering takes too long.

Root cause:

• PagedEditable page-surface overscan used a broad implicit viewport buffer.
• Table row materialization followed that broad page window.
• A fast jump into the table mounted up to 240 rows / 720 cells and produced a local worst frame around 200ms.

Fix:

• Interpret virtualized page overscan literally for page-surface windowing.
• Keep table layout units constrained to the actual visible content range.
• Retain selected unit paths so programmatic selection/editing still materializes the selected row.
• Keep the page_overscan control and route state from the prior slice.

Changed:

• packages/slate-layout/src/react.tsx
  • Derives page-surface overscan from virtualized DOM strategy.
  • Removes the extra implicit page-sized overscan buffer.
  • Adds visible-content-range unit filtering.
  • Keeps selected unit paths mounted even outside the visible range.
• playwright/integration/examples/pagination.test.ts
  • Adds a fast-jump regression asserting bounded rows, cells, DOM, and page surfaces.
• .changeset/paged-editable-virtualized-overscan.md
  • Patch changeset for slate-layout.

Performance proof:

• Before fix, local jump through the stress route hit about 200ms, with 240 rows / 720 cells / 3360 elements.
• After fix, page_overscan=1 fast-jump sweep over 81 scroll positions:
  • p95: about 24ms
  • max local jump: about 99ms
  • max rows: 34
  • max cells: 102
  • max DOM elements: 678
  • max page surfaces: 8

Verification:

• PLAYWRIGHT_BASE_URL=http://localhost:3100 PLAYWRIGHT_RETRIES=0 bunx playwright test playwright/integration/examples/pagination.test.ts --project=chromium --grep "1000-page"
  • Result: 1 passed.
• PLAYWRIGHT_BASE_URL=http://localhost:3100 PLAYWRIGHT_RETRIES=0 bunx playwright test playwright/integration/examples/pagination.test.ts playwright/integration/examples/query-controls.test.ts --project=chromium
  • Result: 20 passed.
• bun --filter slate-layout typecheck
  • Result: passed.
• bun typecheck:site
  • Result: passed.
• bunx tsc --noEmit --project tsconfig.json --pretty false
  • Result: passed.
• bun lint:fix
  • Result: passed; formatted one file.
• bun lint
  • Result: passed.
• perl -e 'alarm 60; exec @ARGV' /Users/zbeyens/git/plate-2/.agents/skills/autoreview/scripts/autoreview --mode local
  • Result: no stdout before alarm; no leftover autoreview process remained.

Browser note:

• Tool discovery did not expose the in-app Browser control, so browser proof is Playwright-owned against http://localhost:3100/examples/pagination.

Performance lane:

• repeated unit: page surfaces and table rows/cells.
• budget: stress route should stay under 80 mounted table rows / 240 cells during a fast jump with default overscan.
• interaction: fast scroll/jump through 1000-page route.
• memory/DOM tag: DOM element count, page surfaces, mounted rows, mounted cells.
• degradation contract: virtualized mode keeps off-viewport content out of native DOM; selected paths are retained for editing.

Completion:

• Goal threshold satisfied.