feat: web setup wizard + admin config/state dir split (#226)

lib/auth/crypto.ts

@@ -1,6 +1,6 @@
 import { createCipheriv, createDecipheriv, randomBytes, createHash } from 'node:crypto';
 import { logger } from '@/lib/logger';
-import { readFileEnv } from '@/lib/read-file-env';
+import { getSessionSecret } from '@/lib/auth/session-secret';
 
 const ALGORITHM = 'aes-256-gcm';
 const IV_LENGTH = 12;
@@ -9,7 +9,7 @@ const TAG_LENGTH = 16;
 const MIN_SECRET_LENGTH = 32;
 
 function getKey(): Buffer {
-  const secret =  process.env.SESSION_SECRET || readFileEnv(process.env.SESSION_SECRET_FILE);
+  const secret = getSessionSecret();
   if (!secret) throw new Error('SESSION_SECRET not configured');
   if (secret.length < MIN_SECRET_LENGTH) {
     throw new Error(

lib/auth/session-secret.ts

@@ -0,0 +1,31 @@
+import { configManager } from '@/lib/admin/config-manager';
+import { readFileEnv } from '@/lib/read-file-env';
+
+/**
+ * Resolve the session secret from any of the supported sources, in priority
+ * order:
+ *   1. SESSION_SECRET env var
+ *   2. SESSION_SECRET_FILE-pointed file
+ *   3. Admin override in config.json (set by the setup wizard)
+ *
+ * Returns an empty string when nothing is configured. Callers must treat
+ * empty as "feature disabled" rather than crashing.
+ *
+ * The configManager fallback exists so the web installer can persist the
+ * secret without touching .env files. It only takes effect if the env vars
+ * aren't set, so existing deployments aren't affected.
+ */
+export function getSessionSecret(): string {
+  const fromEnv = process.env.SESSION_SECRET;
+  if (fromEnv) return fromEnv;
+
+  const fromFile = readFileEnv(process.env.SESSION_SECRET_FILE);
+  if (fromFile) return fromFile;
+
+  const fromAdmin = configManager.get<string>('sessionSecret', '');
+  return fromAdmin || '';
+}
+
+export function hasSessionSecret(): boolean {
+  return getSessionSecret().length > 0;
+}