Fix template deduplication by separating structure comparison from content storage

- Replace content-aware extractCleanTemplate with structure-only extractStructureSignature for template comparison
- Add extractTemplateForStorage to preserve actual content for meaningful template display
- Update generateTemplateSignature to use purely structural comparison ignoring text content
- Remove redundant extractClassSignature function (functionality moved to extractStructureSignature)
- Resolves issue where identical DOM structures created multiple templates due to content differences
- Knowledge cards and other collections now correctly deduplicate to single templates while preserving content for previews

internal/engine/content.go

@@ -2,7 +2,9 @@ package engine
 
 import (
 	"context"
+	"fmt"
 	"slices"
+	"sort"
 	"strings"
 
 	"golang.org/x/net/html"
@@ -62,31 +64,44 @@ func (e *ContentEngine) extractOriginalTemplate(node *html.Node) string {
 	return buf.String()
 }
 
-// extractCleanTemplate extracts a clean template without data-content-id attributes and with placeholder content. Used for collection template variants.
-func (e *ContentEngine) extractCleanTemplate(node *html.Node) string {
+// extractStructureSignature creates a content-agnostic signature for template comparison
+// This only considers DOM structure and class attributes, completely ignoring text content
+func (e *ContentEngine) extractStructureSignature(node *html.Node) string {
+	var signature strings.Builder
+
+	e.walkNodes(node, func(n *html.Node) {
+		if n.Type == html.ElementNode {
+			// Get classes for this element
+			classes := GetClasses(n)
+			if len(classes) > 0 {
+				// Sort classes for consistent comparison
+				sortedClasses := make([]string, len(classes))
+				copy(sortedClasses, classes)
+				sort.Strings(sortedClasses)
+
+				// Add to signature: element[class1,class2,...]
+				signature.WriteString(fmt.Sprintf("%s[%s];", n.Data, strings.Join(sortedClasses, ",")))
+			} else {
+				// Element with no classes
+				signature.WriteString(fmt.Sprintf("%s[];", n.Data))
+			}
+		}
+		// Completely ignore text nodes and their content
+	})
+
+	return signature.String()
+}
+
+// extractTemplateForStorage extracts template HTML while preserving content but removing data-content-id attributes
+func (e *ContentEngine) extractTemplateForStorage(node *html.Node) string {
 	// Clone the node to avoid modifying the original
 	clonedNode := e.cloneNode(node)
 
-	// Remove all data-content-id attributes and replace content with placeholders
+	// Remove all data-content-id attributes but preserve all content
 	e.walkNodes(clonedNode, func(n *html.Node) {
 		if n.Type == html.ElementNode {
 			// Remove data-content-id attribute
 			e.removeAttribute(n, "data-content-id")
-
-			// If this is an .insertr element, replace content with placeholder
-			if e.hasClass(n, "insertr") {
-				placeholderText := e.getPlaceholderForElement(n.Data)
-				// Clear existing children and add placeholder text
-				for child := n.FirstChild; child != nil; {
-					next := child.NextSibling
-					n.RemoveChild(child)
-					child = next
-				}
-				n.AppendChild(&html.Node{
-					Type: html.TextNode,
-					Data: placeholderText,
-				})
-			}
 		}
 	})