epic(perf): Connections sidebar FPS / frame budget @ 120 Hz

[ZhuchkaTriplesix]

Goal

Keep the left Connections tree (and surrounding shell) within frame budget on high-Hz displays so expand/collapse and scroll stay smooth.

Hz	Budget (build + raster)
60	≤ 16.6 ms
120	≤ 8.3 ms
144	≤ 6.9 ms

Measure in profile/release per docs/perf-baseline.md (tree expand + heavy scroll scenarios). Overlay: --dart-define=QUERYA_REFRESH_OVERLAY=true.

Context

Algorithm/memory epic #414 shipped (incl. SDUI tree virtualization). Remaining risk is UI-thread layout/paint on native trees: nested ListView(shrinkWrap) + QueryaAnimatedExpand (AnimatedSize) under the outer SliverList.

Visual parity epic: #718 — implement chrome unify without reintroducing eager Columns.

Children

• Flatten / virtualize native tree (remove nested shrinkWrap lists)
• Narrow selection rebuild fan-out
• Gate or skip height morph on large expands
• Profile checklist + DevTools capture for regressions

Review

Canvas: connection-tree-fps-review

[ZhuchkaTriplesix]

QA execution tracked in #739 (Fluid shell §9–15 + connections tree runbook, DevTools captures @ 120 Hz).