test: pin controller notify count for layout cycle (#122)#129
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Issue #122 questioned whether the post-frame setRenderedSizes notify could be elided. Investigation shows it is structurally required: the notify triggers the build-path switch from the layout widget (with non-interactive placeholder dividers) to the flex widget (with interactive dividers), and notifyListeners cannot legally run during performLayout. These tests pin the resulting notification cadence — one notify on initial mount, two per hide — so a future refactor cannot silently introduce a third redundant cycle or remove the load-bearing one. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Closes #122.
The issue asked whether the post-frame
setRenderedSizesnotify could be elided to avoid a layout retrigger. Investigation shows the notify is structurally required, not wasted:_buildForPhasefromResizableLayout(placeholder, non-interactive dividers) toFlex(interactive dividers withonResizeUpdate). Without it, dividers can't be dragged after the first layout.notifyListeners()triggersmarkNeedsBuild, which is illegal duringperformLayout, so the post-frame defer is required.controller.pixelsis public API — user listeners legitimately expect to be notified when rendered pixels populate._needsLayout = falseis set before the notify, so the resulting rebuild takes the Flex path and never re-enters layout. The "re-trigger" risk is already short-circuited.Empirical measurement: 1 notify on initial mount, 2 notifies per
hide()(one fromsetHidden, one from the post-framesetRenderedSizes). Both convey real state changes.No
lib/changes. Adds two regression tests under a newnotify countgroup that pin the cadence — a future refactor that accidentally adds a third notify or removes the load-bearing one will fail.Test plan
initial mount notifies exactly oncehide produces exactly two notifies🤖 Generated with Claude Code