fix: btg link highlight text

lib/text-highlight.ts

@@ -86,24 +86,33 @@ export function extractMatchedText(
   // Build a single string with paragraph breaks
   const fullText = plainParagraphs.join(" ");
   const normalized = fullText.replace(/\s+/g, " ");
+  const normalizedLower = normalized.toLowerCase();
 
-  const normalizedPrefix = fragment.prefix.replace(/\s+/g, " ");
+  const normalizedPrefix = fragment.prefix.replace(/\s+/g, " ").toLowerCase();
   let searchFrom = 0;
   let matchStart = -1;
 
-  while (searchFrom < normalized.length) {
-    const idx = normalized.indexOf(normalizedPrefix, searchFrom);
+  while (searchFrom < normalizedLower.length) {
+    const idx = normalizedLower.indexOf(normalizedPrefix, searchFrom);
     if (idx === -1) break;
 
     if (fragment.suffix) {
-      const normalizedSuffix = fragment.suffix.replace(/\s+/g, " ");
+      const normalizedSuffix = fragment.suffix
+        .replace(/\s+/g, " ")
+        .toLowerCase();
       const expectedEnd = idx + fragment.length;
       const suffixSearchStart = Math.max(
         idx,
         expectedEnd - normalizedSuffix.length - 20,
       );
-      const suffixSearchEnd = Math.min(normalized.length, expectedEnd + 20);
-      const searchWindow = normalized.slice(suffixSearchStart, suffixSearchEnd);
+      const suffixSearchEnd = Math.min(
+        normalizedLower.length,
+        expectedEnd + 20,
+      );
+      const searchWindow = normalizedLower.slice(
+        suffixSearchStart,
+        suffixSearchEnd,
+      );
       if (searchWindow.includes(normalizedSuffix)) {
         matchStart = idx;
         break;
@@ -117,6 +126,7 @@ export function extractMatchedText(
 
   if (matchStart === -1) return null;
 
+  // Slice from the original (not lowercased) to preserve original casing
   const matchEnd = Math.min(matchStart + fragment.length, normalized.length);
   const matched = normalized.slice(matchStart, matchEnd).trim();
 
@@ -165,11 +175,28 @@ export function findAndHighlightText(fragment: {
     }
   });
 
-  // Build a concatenated string of all text content with node boundaries
+  // Build a concatenated string of all text content with node boundaries.
+  // Insert a space between text nodes from different block-level parents
+  // so that "BACK-TO-GODHEAD" in <div>1</div> and "AN INSTRUMENT" in <div>2</div>
+  // become "BACK-TO-GODHEAD AN INSTRUMENT" instead of "BACK-TO-GODHEADAN INSTRUMENT".
   const segments: { node: Text; start: number; end: number }[] = [];
   let fullText = "";
+  let prevParent: Element | null = null;
   for (const node of allTextNodes) {
     const text = node.textContent || "";
+    const parent = node.parentElement;
+
+    // Add a space separator when crossing into a different block-level parent
+    if (
+      prevParent &&
+      parent !== prevParent &&
+      fullText.length > 0 &&
+      !fullText.endsWith(" ")
+    ) {
+      fullText += " ";
+    }
+    prevParent = parent;
+
     segments.push({
       node,
       start: fullText.length,
@@ -180,26 +207,32 @@ export function findAndHighlightText(fragment: {
 
   // Normalize whitespace for matching
   const normalizedFull = fullText.replace(/\s+/g, " ");
+  const normalizedFullLower = normalizedFull.toLowerCase();
 
-  // Search for the prefix in the full text
-  const normalizedPrefix = fragment.prefix.replace(/\s+/g, " ");
+  // Search for the prefix in the full text (case-insensitive)
+  const normalizedPrefix = fragment.prefix.replace(/\s+/g, " ").toLowerCase();
   let searchFrom = 0;
   let matchStart = -1;
 
-  while (searchFrom < normalizedFull.length) {
-    const idx = normalizedFull.indexOf(normalizedPrefix, searchFrom);
+  while (searchFrom < normalizedFullLower.length) {
+    const idx = normalizedFullLower.indexOf(normalizedPrefix, searchFrom);
     if (idx === -1) break;
 
     // If we have a suffix, verify it appears near the expected length
     if (fragment.suffix) {
-      const normalizedSuffix = fragment.suffix.replace(/\s+/g, " ");
+      const normalizedSuffix = fragment.suffix
+        .replace(/\s+/g, " ")
+        .toLowerCase();
       const expectedEnd = idx + fragment.length;
       const suffixSearchStart = Math.max(
         idx,
         expectedEnd - normalizedSuffix.length - 20,
       );
-      const suffixSearchEnd = Math.min(normalizedFull.length, expectedEnd + 20);
-      const searchWindow = normalizedFull.slice(
+      const suffixSearchEnd = Math.min(
+        normalizedFullLower.length,
+        expectedEnd + 20,
+      );
+      const searchWindow = normalizedFullLower.slice(
         suffixSearchStart,
         suffixSearchEnd,
       );
@@ -217,6 +250,7 @@ export function findAndHighlightText(fragment: {
 
   if (matchStart === -1) return false;
 
+  // Slice from original (not lowercased) to preserve original casing in highlight
   const matchEnd = Math.min(
     matchStart + fragment.length,
     normalizedFull.length,