fix: handle completion when already signed (#3159)

Previously attempting to complete a document which is already completed
you'd get a generic error toast. Now when completing a document that you
have already completed you are redirected to the completed page.

Handles cases where two mutations managed to fire racing eachother.

packages/lib/server-only/document/complete-document-with-token.ts

@@ -80,22 +80,29 @@ export const completeDocumentWithToken = async ({
 
   const legacyDocumentId = mapSecondaryIdToDocumentId(envelope.secondaryId);
 
-  if (envelope.status !== DocumentStatus.PENDING) {
-    throw new Error(`Document ${envelope.id} must be pending`);
-  }
-
   if (envelope.recipients.length === 0) {
     throw new Error(`Document ${envelope.id} has no recipient with token ${token}`);
   }
 
   const [recipient] = envelope.recipients;
 
-  assertRecipientNotExpired(recipient);
-
+  // A retried or duplicate completion request for an already signed
+  // recipient throws a code the router resolves idempotently. This must be
+  // checked before the envelope status guard since the envelope may have
+  // been completed and sealed by the recipient's original request.
   if (recipient.signingStatus === SigningStatus.SIGNED) {
-    throw new Error(`Recipient ${recipient.id} has already signed`);
+    throw new AppError(AppErrorCode.RECIPIENT_ALREADY_SIGNED, {
+      message: `Recipient ${recipient.id} has already signed`,
+      statusCode: 400,
+    });
   }
 
+  if (envelope.status !== DocumentStatus.PENDING) {
+    throw new Error(`Document ${envelope.id} must be pending`);
+  }
+
+  assertRecipientNotExpired(recipient);
+
   if (recipient.signingStatus === SigningStatus.REJECTED) {
     throw new AppError(AppErrorCode.UNKNOWN_ERROR, {
       message: 'Recipient has already rejected the document',
@@ -276,9 +283,15 @@ export const completeDocumentWithToken = async ({
   }
 
   await prisma.$transaction(async (tx) => {
-    await tx.recipient.update({
+    // Conditional update so two concurrent completion requests can't both
+    // proceed: only the request that transitions the recipient to SIGNED
+    // continues, the loser sees a count of 0 and aborts.
+    const { count: updatedRecipientCount } = await tx.recipient.updateMany({
       where: {
         id: recipient.id,
+        signingStatus: {
+          not: SigningStatus.SIGNED,
+        },
       },
       data: {
         signingStatus: SigningStatus.SIGNED,
@@ -288,6 +301,16 @@ export const completeDocumentWithToken = async ({
       },
     });
 
+    // A concurrent request completed the recipient between our initial read
+    // and this transaction. Abort so the winning request handles all side
+    // effects, the router resolves this code idempotently.
+    if (updatedRecipientCount === 0) {
+      throw new AppError(AppErrorCode.RECIPIENT_ALREADY_SIGNED, {
+        message: `Recipient ${recipient.id} has already signed`,
+        statusCode: 400,
+      });
+    }
+
     if (recipientEmail !== recipient.email || recipientName !== recipient.name) {
       await tx.documentAuditLog.create({
         data: createDocumentAuditLogData({