fix: render error messages for invalid templates (#3088)

Currently direct templates can be created without the required
signatures fields for signers.

This means that the document can be fully signed by everyone but will
ultimately fail the sealing step which leaves the document in an
unrecoverable state.

packages/lib/server-only/envelope/get-envelope-for-direct-template-signing.ts

@@ -5,6 +5,7 @@ import { match } from 'ts-pattern';
 import { AppError, AppErrorCode } from '../../errors/app-error';
 import { DocumentAccessAuth, type TDocumentAuthMethods } from '../../types/document-auth';
 import { extractDocumentAuthMethods } from '../../utils/document-auth';
+import { getRecipientsWithMissingFields } from '../../utils/recipients';
 import { extractFieldAutoInsertValues } from '../document/send-document';
 import { getTeamSettings } from '../team/get-team-settings';
 import type { EnvelopeForSigningResponse } from './get-envelope-for-recipient-signing';
@@ -125,6 +126,17 @@ export const getEnvelopeForDirectTemplateSigning = async ({
     });
   }
 
+  const recipientsWithMissingFields = getRecipientsWithMissingFields(
+    envelope.recipients,
+    envelope.recipients.flatMap((envelopeRecipient) => envelopeRecipient.fields),
+  );
+
+  if (recipientsWithMissingFields.length > 0) {
+    throw new AppError(AppErrorCode.MISSING_SIGNATURE_FIELD, {
+      message: 'One or more signers on this direct template are missing a signature field',
+    });
+  }
+
   const settings = await getTeamSettings({ teamId: envelope.teamId });
 
   const sender = settings.includeSenderDetails