fix: clamp preview scroll so over-scrolling doesn't dead-zone scroll-up#11
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renderPreview clamped previewScroll on a value receiver, so the write was discarded and the model's previewScroll grew unbounded on pgdown / wheel-down past the content. The render survived (it re-clamped a local copy each frame), but after over-scrolling, scrolling back up was dead for many keypresses while previewScroll unwound from a huge value. Extract the preview line builder (buildPreviewLines) so Update can bound the scroll against the real line count via maxPreviewScroll, where the mutation actually persists. renderPreview now clamps a local var only, making the value-receiver constraint explicit.
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What
The last finding from the codebase review (Yoda lens).
renderPreviewclampedpreviewScrollwithm.previewScroll = max(0, len(msgLines)-1)- butrenderPreviewhas a value receiver, so that write hits a copy and is discarded. The model'spreviewScrolltherefore grew unbounded on pgdown / wheel-down past the content. The render itself never panicked (it re-clamps a local copy each frame before slicing), but after over-scrolling, scrolling back up was dead for many keypresses whilepreviewScrollunwound from a huge value.Fix
buildPreviewLines(conv, query), shared byrenderPreviewand a newmaxPreviewScroll().Update(pgdown/ctrl+j and wheel-down) viamin(previewScroll+n, maxPreviewScroll())- where the mutation actually persists.renderPreviewnow clamps a local var only, making the value-receiver constraint explicit instead of silently discarding the write.Tests
TestPreviewScrollClampedToContent- hammers pgdown 100× and assertspreviewScrollnever exceedsmaxPreviewScroll, settles at it, and that a single pgup from the bottom visibly moves (no dead zone). Fails under the old discarded-clamp code.TestUpdateMouseScrollfixtures given real messages (an empty conversation now correctly can't scroll).TestRenderPreviewunchanged and passing - confirms the extraction preserved rendering. Coverage up to 70.9%.