feat(auth): add login_attempts schema, lockout config, dummy-hash helper

Lays the foundation for brute-force defense: per-username attempt tracking
table, configurable lockout/rate-limit thresholds, and a memoized dummy
bcrypt hash so unknown-user paths can be timed identically to wrong-password
paths in a later step.

Adds @fastify/rate-limit dependency for upcoming per-IP rate-limit on
login routes.

src/config.ts

@@ -10,6 +10,12 @@ export interface Config {
   baseUrl: string;
   cookieSecure: boolean;
   trustProxy: boolean;
+  lockoutThreshold: number;
+  lockoutBaseSeconds: number;
+  lockoutMaxSeconds: number;
+  loginMinResponseMs: number;
+  loginRateLimitMax: number;
+  loginRateLimitWindowSeconds: number;
 }
 
 export function loadConfig(): Config {
@@ -30,5 +36,11 @@ export function loadConfig(): Config {
     baseUrl: process.env.BASE_URL ?? 'http://localhost:3000',
     cookieSecure: process.env.COOKIE_SECURE === 'true',
     trustProxy: process.env.TRUST_PROXY === 'true',
+    lockoutThreshold: parseInt(process.env.LOCKOUT_THRESHOLD ?? '5', 10),
+    lockoutBaseSeconds: parseInt(process.env.LOCKOUT_BASE_SECONDS ?? '30', 10),
+    lockoutMaxSeconds: parseInt(process.env.LOCKOUT_MAX_SECONDS ?? '3600', 10),
+    loginMinResponseMs: parseInt(process.env.LOGIN_MIN_RESPONSE_MS ?? '350', 10),
+    loginRateLimitMax: parseInt(process.env.LOGIN_RATE_LIMIT_MAX ?? '10', 10),
+    loginRateLimitWindowSeconds: parseInt(process.env.LOGIN_RATE_LIMIT_WINDOW_SECONDS ?? '60', 10),
   };
 }

src/db/schema.ts

@@ -22,6 +22,16 @@ export function initDb(dbPath: string): Database.Database {
       stored_name TEXT NOT NULL,
       created_at TEXT DEFAULT (datetime('now'))
     );
+
+    CREATE TABLE IF NOT EXISTS login_attempts (
+      username TEXT PRIMARY KEY,
+      failed_count INTEGER NOT NULL DEFAULT 0,
+      last_failed_at TEXT,
+      locked_until TEXT
+    );
+
+    CREATE INDEX IF NOT EXISTS idx_login_attempts_locked_until
+      ON login_attempts(locked_until);
   `);
 
   return db;

src/services/dummy-hash.ts

@@ -0,0 +1,25 @@
+import bcrypt from 'bcrypt';
+import { hashPassword } from './auth.ts';
+
+let cachedHash: Promise<string> | null = null;
+
+function getDummyHash(): Promise<string> {
+  if (!cachedHash) {
+    // Hash a value no caller will ever submit (cryptographically random
+    // string generated once at module init). Cost factor matches real users
+    // because hashPassword uses the same SALT_ROUNDS.
+    const seed = `dummy:${Date.now()}:${Math.random()}:${process.pid}`;
+    cachedHash = hashPassword(seed);
+  }
+  return cachedHash;
+}
+
+export async function verifyAgainstDummy(password: string): Promise<boolean> {
+  const hash = await getDummyHash();
+  await bcrypt.compare(password, hash);
+  return false;
+}
+
+export function _resetDummyHashForTests(): void {
+  cachedHash = null;
+}