perf: replace .move(edge: .bottom) transitions with .opacity in LazyVStack to fix motionVectors hang (LUM-795)#24375
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ashleeradka merged 2 commits intoApr 8, 2026
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…Stack to fix motionVectors hang (LUM-795) Co-Authored-By: ashlee@vellum.ai <ashlee@vellum.ai>
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…Stack to fix motionVectors hang (LUM-795) (#24375) * perf: replace .move(edge: .bottom) transitions with .opacity in LazyVStack to fix motionVectors hang (LUM-795) Co-Authored-By: ashlee@vellum.ai <ashlee@vellum.ai> * docs: add LazyVStack transition anti-pattern rule to AGENTS.md and inline warning Co-Authored-By: ashlee@vellum.ai <ashlee@vellum.ai> --------- Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com> Co-authored-by: ashlee@vellum.ai <ashlee@vellum.ai>
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Adds CI-enforced guard tests that scan Swift source files for three known LazyVStack performance anti-patterns: 1. FlexFrameLayout (.frame(maxWidth:) / .frame(maxHeight:)) in cell hierarchy 2. motionVectors transitions (.transition(.move(edge:))) in cell hierarchy 3. withAnimation in scroll handlers (motionVectors cascade) Prevents regression of fixes from PRs #24321, #24375, #24411, #24446, #24530, #24570, #24589. Part of #24613. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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* test: add SwiftUI performance guard tests for LazyVStack anti-patterns Adds CI-enforced guard tests that scan Swift source files for three known LazyVStack performance anti-patterns: 1. FlexFrameLayout (.frame(maxWidth:) / .frame(maxHeight:)) in cell hierarchy 2. motionVectors transitions (.transition(.move(edge:))) in cell hierarchy 3. withAnimation in scroll handlers (motionVectors cascade) Prevents regression of fixes from PRs #24321, #24375, #24411, #24446, #24530, #24570, #24589. Part of #24613. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> * fix: add missing cell files to LAZY_VSTACK_CELL_FILES and remove PR references Adds the 10 allowlisted file basenames to the cell hierarchy list so the allowlist is actually consulted. Removes historical PR numbers from the file header comment per AGENTS.md guidance. Co-Authored-By: Claude <noreply@anthropic.com> * fix: use grep -E for portable ERE alternation in FlexFrame guard BSD grep (macOS default) doesn't support \| in BRE mode. Switch to grep -E with | for alternation so the guard works for local dev too. Co-Authored-By: Claude <noreply@anthropic.com> * fix: add SubagentEventsReader to cell files and escape dots in transition grep Co-Authored-By: Claude <noreply@anthropic.com> --------- Co-authored-by: Vellum Assistant <assistant@vellum.ai> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Replaces
.transition(.opacity.combined(with: .move(edge: .bottom)))with.transition(.opacity)on 4 items inside theLazyVStackinMessageListContentView.swift. The.move(edge: .bottom)component forces SwiftUI to compute the total content height of the LazyVStack duringmotionVectors→measureEstimates, iterating every ForEach child and defeating lazy loading — causing 100+ second main-thread hangs..opacityonly needs the view's own frame, so it's safe inside lazy containers. This is a follow-up to #24321 (LUM-740), which was necessary but insufficient.Also adds a permanent anti-pattern rule to
clients/macos/AGENTS.mdand an inline warning comment above the LazyVStack body to prevent reintroduction by future features copying old patterns.Review & Testing Checklist for Human
.move(edge:)transitions exist inside the LazyVStack body (the other.move(edge:)usages in the chat area are all in overlays outside the LazyVStack and are unaffected)Notes
.move(edge:)transitions in the codebase (ChatView overlays, ComposerView, error toasts, etc.) are not inside a LazyVStack and don't trigger the measurement issue — they are intentionally left unchangedLink to Devin session: https://app.devin.ai/sessions/d11994a0494e456ea259a789e3b41f6a
Requested by: @ashleeradka