security: v2.0 — AES-GCM crypto, SSRF guards, rate limits, hardening

Breaking wire-format change: dual-read (V1+V2) / single-write (V2) so
existing user secrets, stored messages, and inter-tenant key keep
working. Old clients and relays lose cross-version chat until both
sides are upgraded.

Relay
- Switch clientEncrypt/masterEncrypt to AES-256-GCM with HKDF-derived
  per-ciphertext salts; keep CBC-V1 fallback on decrypt only.
- On-bootstrap migration re-envelopes tenant secret_encrypted and the
  inter-tenant key to GCM-V2 (idempotent).
- CORS: stop reflecting arbitrary Origin; allow own origin + optional
  RELAY_CORS_ORIGINS env allowlist; drop Access-Control-Allow-Credentials.
- Generic error messages replace "no such user: <name>" enumeration.
- Exception messages no longer echoed back; logged server-side.
- Collab-lock max hold capped at 10min so a member can't grief-refresh
  forever.
- Attachment filenames validated against hex.<ext> pattern.
- Passwords min length 10; /api/account/password rate-limited.

App / Electron client
- Shared hyprcrdRelayEncrypt/Decrypt helpers (GCM-V2 write, V1 read).
- Chat + collab-buckets plugins delegate to the shared helpers.
- Poll + push + attachments migrated to the dual-format path.
- /api/relay/settings GET returns has_key boolean; secret never echoed.
- Setup endpoint now CSRF-checked.
- SSRF: CURLOPT_PROTOCOLS restricted to HTTP(S) everywhere; bookmarks
  favicon fetch also blocks private/loopback/link-local.
- Login / password-change rate limiter moved to DB-backed IP keying.
- Passwords min length 10 throughout.
- Zip import enforces per-file (25MB) and total (500MB) caps, extension
  allowlist, no-overwrite.
- Verbose relay-push debug gated behind APP_DEBUG env.

Version bumped to 2.0.0 (protocol-breaking).

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

public/plugins/chat/backend.php

@@ -108,24 +108,20 @@ function chatRelaySettings(): array {
     ];
 }
 
-/** Same envelope format as the existing relay sync (HYPRCRD-RELAY-V1). */
+/** Dual-format envelope shared with the relay sync path. Writes V2
+ *  (AES-GCM + HKDF), reads V2 + legacy V1 (CBC). Delegates to the central
+ *  helpers so the format stays in lock-step with src/bootstrap.php and
+ *  the relay's crypto.php. */
 function chatEncrypt(string $plain, string $relayKey): string {
-    $encKey = substr(hash('sha256', $relayKey), 0, 32);
-    $iv = random_bytes(16);
-    $cipher = openssl_encrypt($plain, 'aes-256-cbc', $encKey, OPENSSL_RAW_DATA, $iv);
-    return "HYPRCRD-RELAY-V1\n" . base64_encode($iv . $cipher);
+    return hyprcrdRelayEncrypt($plain, $relayKey);
 }
 
 function chatDecrypt(string $envelope, string $relayKey): string {
-    if (!str_starts_with($envelope, 'HYPRCRD-RELAY-V1')) return '';
-    $b64 = trim(substr($envelope, strlen('HYPRCRD-RELAY-V1') + 1));
-    $raw = base64_decode($b64);
-    if (!$raw || strlen($raw) < 17) return '';
-    $encKey = substr(hash('sha256', $relayKey), 0, 32);
-    $iv = substr($raw, 0, 16);
-    $cipher = substr($raw, 16);
-    $result = openssl_decrypt($cipher, 'aes-256-cbc', $encKey, OPENSSL_RAW_DATA, $iv);
-    return $result !== false ? $result : '';
+    // Old behaviour returned '' for non-envelope strings; preserve that.
+    if (!str_starts_with($envelope, HYPRCRD_RELAY_GCM_MAGIC) && !str_starts_with($envelope, HYPRCRD_RELAY_CBC_MAGIC)) {
+        return '';
+    }
+    return hyprcrdRelayDecrypt($envelope, $relayKey);
 }
 
 function chatGetState(string $key, $default = null) {