diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 00000000..a8710b28
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2024-05-24 - Timing Attack via Length Check Fast Path
+**Vulnerability:** A length check before calling `crypto.timingSafeEqual` for variable-length secrets (like A2A tokens) created a short-circuit fast path, leaking the length of the secret via timing differences.
+**Learning:** `crypto.timingSafeEqual` throws if buffer lengths do not match, tempting developers to check length first. However, doing so destroys the constant-time guarantee because different lengths return immediately.
+**Prevention:** Always hash both the user input and the expected secret using a cryptographic hash function (e.g., SHA-256) to ensure they are the exact same fixed length before calling `timingSafeEqual`.
diff --git a/src/cli/commands/serve.ts b/src/cli/commands/serve.ts
index 2c37293e..0bf874ce 100644
--- a/src/cli/commands/serve.ts
+++ b/src/cli/commands/serve.ts
@@ -346,13 +346,10 @@ export async function handleServeCommand(_options: unknown, command: Command) {
 
           let isAuthenticated = false;
           if (scheme?.toLowerCase() === 'bearer' && token) {
-            const tokenBuffer = Buffer.from(token);
+            const tokenHash = crypto.createHash('sha256').update(token).digest();
             for (const authToken of authTokens) {
-              const authTokenBuffer = Buffer.from(authToken);
-              if (
-                tokenBuffer.length === authTokenBuffer.length &&
-                crypto.timingSafeEqual(tokenBuffer, authTokenBuffer)
-              ) {
+              const authHash = crypto.createHash('sha256').update(authToken).digest();
+              if (crypto.timingSafeEqual(tokenHash, authHash)) {
                 isAuthenticated = true;
                 break;
               }
diff --git a/tests/integration/prompt_templates.test.ts b/tests/integration/prompt_templates.test.ts
index 21905259..f1360d78 100644
--- a/tests/integration/prompt_templates.test.ts
+++ b/tests/integration/prompt_templates.test.ts
@@ -36,7 +36,9 @@ describe('Prompt templates', () => {
 
     expect(planSystem).toContain('You are SalmonLoop.');
     expect(patchSystem).toContain('You are PATCH, a phase-native diff compiler.');
-    expect(autopilotSystem).toContain('You are a senior software engineer running in "autopilot" mode.');
+    expect(autopilotSystem).toContain(
+      'You are a senior software engineer running in "autopilot" mode.',
+    );
     expect(answerSystem).toContain('You are a coding assistant in "answer" mode.');
     expect(researchSystem).toContain('You are a research assistant.');
   });