fix: add validation for empty hosts in round robin reassignment (#22429)

* fix: add validation for empty hosts in round robin reassignment

- Add check for empty availableUsers array before calling getLuckyUser
- Throw RoundRobinHostsUnavailableForBooking error instead of 500 error
- Use existing error infrastructure with 409 status code and localized message
- Prevents runtime errors when no round robin hosts are available for reassignment

Co-Authored-By: joe@cal.com <joe@cal.com>

* fix: check eventType.hosts.length directly for empty hosts validation

- Move validation to check eventType.hosts.length === 0 immediately after hosts array setup
- Remove later validation after ensureAvailableUsers to catch issue earlier
- Follows user feedback to check hosts array directly instead of availableUsers

Co-Authored-By: joe@cal.com <joe@cal.com>

* fix: update translation message for round robin hosts unavailable error

- Make error message clearer about event type having no hosts
- Change from 'No Round Robin hosts is available for booking' to 'No hosts are available in this event type for round robin booking'

Co-Authored-By: joe@cal.com <joe@cal.com>

* Change error for event type no hosts

* fix: add ErrorCode.EventTypeNoHosts to switch statement for 400 status code

Addresses GitHub comment from keithwillcode to ensure EventTypeNoHosts
error returns proper 400 Bad Request status instead of defaulting to 500.

Co-Authored-By: joe@cal.com <joe@cal.com>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: joe@cal.com <joe@cal.com>
Co-authored-by: Joe Au-Yeung <65426560+joeauyeung@users.noreply.github.com>

apps/web/public/static/locales/en/common.json

@@ -3361,5 +3361,6 @@
   "license_validation_failed": "Failed to validate license key",
   "license_key_saved": "License key saved successfully",
   "timezone_mismatch_tooltip": "You are viewing the report based on your profile timezone ({{userTimezone}}), while your browser is set to timezone ({{browserTimezone}})",
+  "event_type_no_hosts": "No hosts are assigned to event type",
   "ADD_NEW_STRINGS_ABOVE_THIS_LINE_TO_PREVENT_MERGE_CONFLICTS": "↑↑↑↑↑↑↑↑↑↑↑↑↑ Add your new strings above here ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑"
 }

packages/features/ee/round-robin/roundRobinReassignment.ts

@@ -20,6 +20,7 @@ import {
   enrichHostsWithDelegationCredentials,
   enrichUserWithDelegationCredentialsIncludeServiceAccountKey,
 } from "@calcom/lib/delegationCredential/server";
+import { ErrorCode } from "@calcom/lib/errorCodes";
 import { getEventName } from "@calcom/lib/event";
 import { IdempotencyKeyService } from "@calcom/lib/idempotencyKey/idempotencyKeyService";
 import { isPrismaObjOrUndefined } from "@calcom/lib/isPrismaObj";
@@ -99,6 +100,10 @@ export const roundRobinReassignment = async ({
         createdAt: new Date(0), // use earliest possible date as fallback
       }));
 
+  if (eventType.hosts.length === 0) {
+    throw new Error(ErrorCode.EventTypeNoHosts);
+  }
+
   const roundRobinHosts = eventType.hosts.filter((host) => !host.isFixed);
 
   const originalOrganizer = booking.user;

packages/lib/errorCodes.ts

@@ -23,4 +23,5 @@ export enum ErrorCode {
   BookerLimitExceededReschedule = "booker_limit_exceeded_error_reschedule",
   BookingNotAllowedByRestrictionSchedule = "booking_not_allowed_by_restriction_schedule_error",
   RestrictionScheduleNotFound = "restriction_schedule_not_found_error",
+  EventTypeNoHosts = "event_type_no_hosts",
 }

packages/lib/server/getServerErrorFromUnknown.ts

@@ -111,6 +111,7 @@ function getStatusCode(cause: Error | ErrorWithCode): number {
     case ErrorCode.BookingNotAllowedByRestrictionSchedule:
     case ErrorCode.BookerLimitExceeded:
     case ErrorCode.BookerLimitExceededReschedule:
+    case ErrorCode.EventTypeNoHosts:
       return 400;
     // 409 Conflict
     case ErrorCode.NoAvailableUsersFound: