feat: add JWT blacklist for logout with TTL cleanup

blacklistJwt() adds token to in-memory blacklist until its natural expiry.
verifyJwt() checks blacklist before signature verification.
Cleanup interval removes expired entries every 10 minutes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/middleware/jwt.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, afterEach } from 'vitest'
-import { createJwt, verifyJwt } from './jwt.js'
+import { createJwt, verifyJwt, blacklistJwt } from './jwt.js'
 
 describe('JWT', () => {
   afterEach(() => {
@@ -66,4 +66,17 @@ describe('JWT', () => {
     expect(verifyJwt('a.b')).toBeNull()
     expect(verifyJwt('a.b.c.d')).toBeNull()
   })
+
+  it('rejects blacklisted JWT (logout)', () => {
+    const token = createJwt('pubkey-logout', 'bot-logout')
+
+    // Token works before blacklisting
+    expect(verifyJwt(token)).not.toBeNull()
+
+    // Blacklist the token
+    blacklistJwt(token)
+
+    // Token is now rejected
+    expect(verifyJwt(token)).toBeNull()
+  })
 })

server/src/middleware/jwt.ts

@@ -7,6 +7,29 @@ if (!process.env.JWT_SECRET && process.env.NODE_ENV === 'production') {
 const JWT_SECRET = process.env.JWT_SECRET || randomBytes(32).toString('hex')
 const JWT_EXPIRY = 24 * 60 * 60 // 24 hours
 
+// JWT blacklist for logout — tokens are blacklisted until they would expire naturally
+const blacklist = new Map<string, number>() // token -> expiry timestamp (seconds)
+
+/** Blacklist a JWT so it can no longer be verified. */
+export function blacklistJwt(token: string): void {
+  const parts = token.split('.')
+  if (parts.length !== 3) return
+  try {
+    const decoded = JSON.parse(Buffer.from(parts[1], 'base64url').toString()) as JwtPayload
+    if (decoded.exp) {
+      blacklist.set(token, decoded.exp)
+    }
+  } catch { /* ignore malformed tokens */ }
+}
+
+// Clean up expired blacklist entries every 10 minutes
+export const blacklistCleanupInterval = setInterval(() => {
+  const now = Math.floor(Date.now() / 1000)
+  for (const [token, exp] of blacklist) {
+    if (now >= exp) blacklist.delete(token)
+  }
+}, 10 * 60 * 1000)
+
 if (!process.env.JWT_SECRET) {
   logger.warn('jwt', 'JWT_SECRET not set — tokens will invalidate on server restart')
 }
@@ -45,6 +68,9 @@ export function verifyJwt(token: string): JwtPayload | null {
     const parts = token.split('.')
     if (parts.length !== 3) return null
 
+    // Check blacklist before expensive signature verification
+    if (blacklist.has(token)) return null
+
     const [header, payload, signature] = parts
     const expectedSig = createHmac('sha256', JWT_SECRET)
       .update(`${header}.${payload}`)