diff --git a/src/lib/client/highlight-token-alignment.ts b/src/lib/client/highlight-token-alignment.ts
index 26210ad..dd560bf 100644
--- a/src/lib/client/highlight-token-alignment.ts
+++ b/src/lib/client/highlight-token-alignment.ts
@@ -36,6 +36,29 @@ export function findBestHighlightTokenMatch(
 
   if (!patternLen || !normalizedTargets.length) return responseBase;
 
+  // Most viewer highlights are exact token sequences. Resolve those in one
+  // linear pass before entering the fuzzy window search, which is expensive
+  // enough to stall the UI when the target is a full HTML/TXT/MD document.
+  const firstPatternToken = normalizedPattern[0];
+  for (let start = 0; start < normalizedTargets.length; start += 1) {
+    if (normalizedTargets[start] !== firstPatternToken) continue;
+    let matches = true;
+    for (let offset = 1; offset < normalizedPattern.length; offset += 1) {
+      if (normalizedTargets[start + offset] !== normalizedPattern[offset]) {
+        matches = false;
+        break;
+      }
+    }
+    if (matches) {
+      return {
+        start,
+        end: start + normalizedPattern.length - 1,
+        rating: 1,
+        lengthDiff: 0,
+      };
+    }
+  }
+
   const patternTokenCount = normalizedPattern.length;
   const minWindowTokens = Math.max(1, Math.floor(patternTokenCount * 0.6));
   const maxWindowTokens = Math.max(
diff --git a/tests/unit/highlight-token-alignment.vitest.spec.ts b/tests/unit/highlight-token-alignment.vitest.spec.ts
index 7ee3212..32fc7d5 100644
--- a/tests/unit/highlight-token-alignment.vitest.spec.ts
+++ b/tests/unit/highlight-token-alignment.vitest.spec.ts
@@ -19,6 +19,21 @@ const alignmentWords = (
   }));
 
 describe('shared viewer highlight token alignment', () => {
+  test('finds an exact sentence in a large document without entering fuzzy comparison', () => {
+    const targets = Array.from({ length: 20_000 }, (_, index) => `token-${index}`);
+    targets.splice(15_000, 4, 'the', 'exact', 'sentence', 'here');
+
+    expect(findBestHighlightTokenMatch(
+      ['the', 'exact', 'sentence', 'here'],
+      targets,
+    )).toEqual({
+      start: 15_000,
+      end: 15_003,
+      rating: 1,
+      lengthDiff: 0,
+    });
+  });
+
   test('matches a complete Japanese sentence using locale-aware token count', () => {
     const sentence = 'これは日本語です。';
     const patternTokens = segmentWords(sentence, 'ja').map((token) => token.text);