Batch compact-stacked wrapping detection to reduce forced reflows

[churnish]

Problem

hasWrappedPairs() performs forced reflows inside ResizeObserver callbacks. The detection flow per card:

1. Remove compact-stacked class
2. Force reflow (void cardEl.offsetHeight)
3. Call getBoundingClientRect() on every .pair-left and .pair-right

With 50 visible compact cards each having 3-4 pairs, a pane resize triggers ~400 synchronous layout reads. The compactWidthCache WeakMap bounds this to once per unique width per card, but the first-time cost per width change remains O(pairs × cards).

Proposed solution

Batch the wrapping detection into a single read-then-write pass across all compact cards, matching the pattern syncResponsiveClasses already uses:

1. Write phase: Remove compact-stacked from all compact cards with cache misses
2. Single forced reflow
3. Read phase: Run hasWrappedPairs() on all cards, collect results
4. Write phase: Apply compact-stacked where needed, update caches

This collapses N forced reflows into 1.

Affected code

• src/bases/shared-renderer.ts — Bases per-card RO callback
• src/shared/card-renderer.tsx — Datacore per-card RO callback
• src/shared/property-helpers.ts — hasWrappedPairs()

Context

Session c3322c8e-cf10-459c-bc94-2060a0ef89ec — triaged as 5.2 (cache-bounded burst, marginal gain vs restructuring cost).

🤖 Generated with Claude Code

[churnish]

Implemented in session de51cca4-cb8b-486b-94fc-94dc0adf54f2.

• RAF-batched read/write cycle collapses N forced reflows into 1 per document per frame
• Per-document partitioning (pendingCardsByDoc Map) for popout window safety
• Grid row-level sync: if any card in a CSS Grid row wraps, all cards in that row get compact-stacked
• compactWidthCache (WeakMap) prevents re-evaluation on height-only changes
• 12 tests covering batch detection, row sync, cross-document isolation, and edge cases

Commit: a4bdba4 (+ audit fixes uncommitted)

🤖 Generated with Claude Code