TT-7579

[sarahentzel]

Why it’s hard to reproduce: the grid virtualizes rows (TT-6986). pageSize was measured once. After paste/save the first paint is a short table (no spacers yet). If that measure sees only a few rows of height, pageSize sticks at ~5 and later sections never mount. On a layout where the inner pane is already the full viewport, the first measure is large enough and everything shows.

A second failure mode: AppLayout is also overflow: auto. If that parent is what actually scrolls, the sheet kept curTop at 1, so scrolling through the blank padding never brought in sections 3–7.

Fix: measure how many rows fit in the visible window, not the short first table; grow the window if unmounted rows are sitting in view as padding; listen to ancestor scroll (capture) so the window moves when AppLayout scrolls.

[Copilot]

Pull request overview

This PR addresses hard-to-reproduce PlanSheet virtualization failures caused by early/incorrect viewport measurement and by ancestor scrolling (e.g., AppLayout scrolling instead of the sheet), which could prevent later sections from mounting.

Changes:

• Extracts and centralizes sheet windowing + viewport math into a reusable sheetWindow module.
• Computes pageSize based on the visible clip (accounting for clipping/scrolling ancestors) rather than the initial short table paint.
• Listens to ancestor scroll via capture, adds a ResizeObserver, and adjusts scroll/top padding behavior so the mounted window advances correctly.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/renderer/src/components/Sheet/sheetWindow.ts	New shared utilities for windowing, clip measurement, and scroll-target detection used by the virtualized sheet.
src/renderer/src/components/Sheet/sheetWindow.test.ts	Unit tests covering window sizing, clip calculations, and scroll-target detection.
src/renderer/src/components/Sheet/PlanSheet.tsx	Integrates the new window/clip helpers to fix initial measurement and ancestor-scroll virtualization edge cases.

Suppressed comments (1)

src/renderer/src/components/Sheet/PlanSheet.tsx:1351

• sheetClip() can return null (by type), but this effect uses clip.scrollTop and clip.getBoundingClientRect() without a null check. Since scroller is already validated as non-null, default clip to scroller to satisfy strict null checks and avoid potential runtime issues if sheetClip() ever returns null.

    const clip = sheetClip();
    const pad = topPadElRef.current;
    const floor = scrollTopFloorForPad(
      clip.scrollTop,
      clip.getBoundingClientRect().top,
      pad?.getBoundingClientRect().bottom ?? 0,

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[gtryus]

Well, this window logic looks more complicated to me and I can't claim I understood this code like I did the code that used to be there. But hopefully AI got it right.