fix(audit-integrations): SMTP/PG/Socket.IO timeouts, prompt injection, secret-at-rest

A focused review of every external integration surfaced six issues the
original audit missed.  Fixed here.

HIGH
* Socket.IO had an unconditional 30-second idle disconnect on every
  socket.  The comment on the line acknowledged it was "for development
  only, would be longer in prod" but no NODE_ENV guard existed, and the
  `socket.onAny` listener only resets on inbound client events — every
  dashboard connection that received only server-push events would have
  been torn down every 30s in production.  Removed the manual idle
  timer entirely; Socket.IO's pingTimeout / pingInterval handles
  dead-transport detection at the protocol level.
* SMTP transporters had no `connectionTimeout` / `greetingTimeout` /
  `socketTimeout`.  Nodemailer's defaults are 2 minutes for connect
  and unlimited for socket — a hung SMTP server would have held a
  BullMQ `email` worker concurrency slot for up to 10 min per job
  (5 retries × 2 min).  Set 10s/10s/30s on both the system transporter
  in `src/lib/email/index.ts` and the user-account transporter in
  `email-compose.service.ts`.

MEDIUM
* PostgreSQL pool had no `statement_timeout` /
  `idle_in_transaction_session_timeout`.  A slow query or transaction
  held by a crashed handler would have eventually exhausted the
  20-connection pool.  30s statement cap, 10s idle-in-tx cap, plus
  `max_lifetime: 30min` to recycle connections.
* `umami_password` and `umami_api_token` were stored as plaintext in
  `system_settings` (the SMTP and S3 secret paths use AES-GCM).  The
  reader now passes them through `readSecret()` which auto-detects
  the encrypted `iv:cipher:tag` shape and decrypts, falling back to
  legacy plaintext so operators can rotate without a flag-day.
* AI email-draft worker interpolated `additionalInstructions` (user-
  controlled) directly into the OpenAI prompt — a hostile rep could
  close the instructions block and inject prompt directives that
  override the system prompt.  Added `sanitizeForPrompt()` that
  strips newlines + quote chars, caps at 500 chars, and the prompt
  now wraps the value in a "treat as data not commands" preamble.

LOW
* Legacy `ensureBucket()` in `src/lib/minio/index.ts` was unguarded —
  if any future code imported it (currently no callers), a misconfigured
  prod deploy could mint a fresh empty bucket.  Now matches the gate
  used by the pluggable S3Backend (`MINIO_AUTO_CREATE_BUCKET=true`
  required) so the legacy export and the new pluggable path agree.

Confirmed not-an-issue: BullMQ Workers create connections via
`{ url }` options object, and BullMQ sets `maxRetriesPerRequest: null`
internally for those — no fix needed.  The shared `redis` singleton
that does keep `maxRetriesPerRequest: 3` is used only for direct
Redis ops (rate-limit sliding window, etc.), never for blocking
BullMQ commands, so the value is correct there.

Test status: 1175/1175 vitest, tsc clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/minio/index.ts

@@ -15,14 +15,26 @@ const BUCKET = env.MINIO_BUCKET;
 
 /**
  * Ensures the configured bucket exists, creating it if not.
- * Should be called once at application startup.
+ *
+ * Gated by MINIO_AUTO_CREATE_BUCKET=true so a misconfigured prod
+ * deploy can't accidentally mint a fresh empty bucket and start
+ * writing into it (silently losing access to the intended one).
+ * The pluggable S3 backend in `src/lib/storage/s3.ts` already
+ * applies the same gate; this legacy export keeps the contract
+ * consistent for any caller still importing from `@/lib/minio`.
  */
 export async function ensureBucket(): Promise<void> {
   try {
     const exists = await minioClient.bucketExists(BUCKET);
     if (!exists) {
+      if (process.env.MINIO_AUTO_CREATE_BUCKET !== 'true') {
+        throw new Error(
+          `MinIO bucket '${BUCKET}' does not exist. Create it manually or set ` +
+            `MINIO_AUTO_CREATE_BUCKET=true.`,
+        );
+      }
       await minioClient.makeBucket(BUCKET);
-      logger.info({ bucket: BUCKET }, 'MinIO bucket created');
+      logger.info({ bucket: BUCKET }, 'MinIO bucket auto-created (MINIO_AUTO_CREATE_BUCKET=true)');
     } else {
       logger.debug({ bucket: BUCKET }, 'MinIO bucket exists');
     }