Merge remote-tracking branch 'origin/main' into pr-2848

# Conflicts:
#	packages/lib/constants/app.ts

packages/lib/constants/app.ts

@@ -1,4 +1,6 @@
 import { env } from '@documenso/lib/utils/env';
+import { AppError, AppErrorCode } from '../errors/app-error';
+import { SignatureLevel, type TSignatureLevel } from '../types/signature-level';
 
 export const APP_DOCUMENT_UPLOAD_SIZE_LIMIT = Number(env('NEXT_PUBLIC_DOCUMENT_SIZE_UPLOAD_LIMIT')) || 50;
 
@@ -34,3 +36,54 @@ export const NEXT_PRIVATE_USE_PLAYWRIGHT_PDF = () => env('NEXT_PRIVATE_USE_PLAYW
 
 export const NEXT_PRIVATE_SIGNING_TIMESTAMP_AUTHORITY = () => env('NEXT_PRIVATE_SIGNING_TIMESTAMP_AUTHORITY');
 export const NEXT_PRIVATE_SIGNING_REASON = () => env('NEXT_PRIVATE_SIGNING_REASON') ?? 'Signed by Documenso';
+
+/**
+ * Whether this Documenso instance is running in CSC (Cloud Signature Consortium) mode.
+ *
+ * CSC mode routes signing through a third-party Trust Service Provider for
+ * Advanced and Qualified Electronic Signatures (AES/QES). It is instance-wide
+ * and mutually exclusive with the other signing transports.
+ */
+export const IS_INSTANCE_CSC_MODE = (): boolean => {
+  if (typeof window === 'undefined') {
+    return env('NEXT_PRIVATE_SIGNING_TRANSPORT') === 'csc';
+  }
+
+  return env('NEXT_PUBLIC_SIGNING_TRANSPORT_IS_CSC') === 'true';
+};
+
+/**
+ * The default signature level applied to envelopes created on a CSC-mode
+ * instance when the caller doesn't specify one (or asks for `SES` and the
+ * resolver is in loose-coerce mode).
+ *
+ * Set via `NEXT_PRIVATE_SIGNING_CSC_SIGNATURE_LEVEL`; accepts `AES` or `QES`
+ * only; defaults to `AES` when unset. An explicit `AES`/`QES` request on
+ * envelope create still passes through unchanged — this constant only affects
+ * the coerced default.
+ *
+ * Throws on an invalid value rather than silently falling back. A typo here
+ * (e.g. `qes`) would otherwise silently downgrade qualified-tier instances
+ * to advanced-tier, which has legal consequences.
+ *
+ * Only consulted on CSC-mode instances. Non-CSC instances always default to
+ * `SES` regardless of this var.
+ */
+export const CSC_INSTANCE_SIGNATURE_LEVEL = (): TSignatureLevel => {
+  // Cast through `string | undefined` because shells can deliver
+  // `NEXT_PRIVATE_SIGNING_CSC_SIGNATURE_LEVEL=` as an empty string at runtime
+  // — the typed env signature narrows to `'AES' | 'QES' | undefined` only.
+  const value = env('NEXT_PRIVATE_SIGNING_CSC_SIGNATURE_LEVEL');
+
+  if (!value) {
+    return SignatureLevel.AES;
+  }
+
+  if (value !== SignatureLevel.AES && value !== SignatureLevel.QES) {
+    throw new AppError(AppErrorCode.NOT_SETUP, {
+      message: `NEXT_PRIVATE_SIGNING_CSC_SIGNATURE_LEVEL must be '${SignatureLevel.AES}' or '${SignatureLevel.QES}', got '${value}'.`,
+    });
+  }
+
+  return value;
+};