diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..4168133
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2026-07-01 - Byte Array to Hex String Conversion Optimization
+**Learning:** In Java 21, using `String.format("%02x", b)` inside a loop to convert a byte array to a hex string causes unnecessary allocations and is significantly slower than native alternatives.
+**Action:** Use `java.util.HexFormat.of().formatHex(bytes)` for faster and allocation-free conversions from byte arrays to hex strings in this codebase.
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index 9c59593..c0335f9 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -121,12 +121,10 @@ private String contentHash(MultipartFile file) {
             }
 
             byte[] raw = digest.digest();
-            StringBuilder hex = new StringBuilder(raw.length * 2);
-            for (byte b : raw) {
-                hex.append(String.format("%02x", b));
-            }
 
-            return hex.toString();
+            // Bolt Performance Optimization:
+            // Use HexFormat instead of String.format loop for performance.
+            return java.util.HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {