fix: collapse long proposed plans by truncating DOM content

The collapsed state rendered the full plan markdown in the DOM and
relied on CSS overflow-hidden to clip it visually. This caused the
browser test to correctly detect hidden text still present in
document.body.textContent.

Compute markdownPreview whenever the plan is collapsible (not only
when a checklist is present) so the collapsed state renders a
truncated preview instead of the full content.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: BunsDev

apps/web/src/components/chat/ProposedPlanCard.tsx

@@ -58,16 +58,16 @@ export const ProposedPlanCard = memo(function ProposedPlanCard({
 
   const hasChecklist = checklistItems.length > 0;
 
-  // Build a preview for the markdown section (only used when checklist is present).
-  const markdownPreview = useMemo(() => {
-    if (!hasChecklist) return null;
-    return buildCollapsedProposedPlanPreviewMarkdown(planMarkdown, { maxLines: 6 });
-  }, [planMarkdown, hasChecklist]);
-
   // When no checklist items are found, fall back to the original markdown-only view.
   const lineCount = planMarkdown.split("\n").length;
   const canCollapseMarkdown = planMarkdown.length > 900 || lineCount > 20;
 
+  // Build a truncated preview so collapsed plans never leak hidden content into the DOM.
+  const markdownPreview = useMemo(() => {
+    if (!canCollapseMarkdown) return null;
+    return buildCollapsedProposedPlanPreviewMarkdown(planMarkdown, { maxLines: 6 });
+  }, [planMarkdown, canCollapseMarkdown]);
+
   const handleDownload = () => {
     downloadPlanAsTextFile(downloadFilename, saveContents);
   };