Throw proper error on duplicate emailing domain (#22790)

Adding an emailing domain that already exists blew up with a raw
QueryFailedError and the client just saw a generic "An error occurred".
The unique index on domain is global, so the workspace-scoped existence
check never caught rows owned by another workspace.

Now the check is unscoped and throws an EmailingDomainException mapped
to CONFLICT with a proper user-facing message, in both the
createEmailingDomain mutation and the email group channel flow. Also
dropped the hardcoded catch-all snackbar on the new channel page so
server messages actually reach the user.

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packages/twenty-front/src/modules/settings/accounts/components/SettingsAccountsNewEmailGroupChannel.tsx

@@ -10,7 +10,6 @@ import { Section } from 'twenty-ui/layout';
 import { useCreateEmailGroupChannel } from '@/settings/accounts/hooks/useCreateEmailGroupChannel';
 import { SaveAndCancelButtons } from '@/settings/components/SaveAndCancelButtons/SaveAndCancelButtons';
 import { SettingsPageContainer } from '@/settings/components/SettingsPageContainer';
-import { useSnackBar } from '@/ui/feedback/snack-bar-manager/hooks/useSnackBar';
 import { SettingsTextInput } from '@/ui/input/components/SettingsTextInput';
 import { SettingsPageLayout } from '@/settings/components/layout/SettingsPageLayout';
 import { useNavigateSettings } from '~/hooks/useNavigateSettings';
@@ -18,7 +17,6 @@ import { useNavigateSettings } from '~/hooks/useNavigateSettings';
 export const SettingsAccountsNewEmailGroupChannel = () => {
   const { t } = useLingui();
   const navigate = useNavigateSettings();
-  const { enqueueErrorSnackBar } = useSnackBar();
   const { createEmailGroupChannel, loading } = useCreateEmailGroupChannel();
 
   const [handle, setHandle] = useState('');
@@ -27,22 +25,16 @@ export const SettingsAccountsNewEmailGroupChannel = () => {
   const canSave = isHandleValidEmail && !loading;
 
   const handleSave = useCallback(async () => {
-    try {
-      const result = await createEmailGroupChannel(handle);
-      const messageChannelId =
-        result.data?.createEmailGroupChannel.messageChannel.id;
+    const result = await createEmailGroupChannel(handle);
+    const messageChannelId =
+      result.data?.createEmailGroupChannel.messageChannel.id;
 
-      if (messageChannelId) {
-        navigate(SettingsPath.EmailGroupChannelDetail, {
-          messageChannelId,
-        });
-      }
-    } catch {
-      enqueueErrorSnackBar({
-        message: t`Failed to create email channel. Email channels may not be configured on this server.`,
+    if (messageChannelId) {
+      navigate(SettingsPath.EmailGroupChannelDetail, {
+        messageChannelId,
       });
     }
-  }, [createEmailGroupChannel, handle, navigate, enqueueErrorSnackBar, t]);
+  }, [createEmailGroupChannel, handle, navigate]);
 
   return (
     <SettingsPageLayout

packages/twenty-front/src/modules/settings/accounts/hooks/useCreateEmailGroupChannel.ts

@@ -10,6 +10,7 @@ import { CREATE_EMAIL_GROUP_CHANNEL } from '@/settings/accounts/graphql/mutation
 import { GET_MY_CONNECTED_ACCOUNTS } from '@/settings/accounts/graphql/queries/getMyConnectedAccounts';
 import { GET_MY_MESSAGE_CHANNELS } from '@/settings/accounts/graphql/queries/getMyMessageChannels';
 import { GET_ALL_EMAILING_DOMAINS } from '@/settings/emailing-domains/graphql/queries/getAllEmailingDomains';
+import { useSnackBar } from '@/ui/feedback/snack-bar-manager/hooks/useSnackBar';
 
 type CreateEmailGroupChannelResult = {
   createEmailGroupChannel: {
@@ -33,6 +34,8 @@ type CreateEmailGroupChannelVariables = {
 };
 
 export const useCreateEmailGroupChannel = () => {
+  const { enqueueErrorSnackBar } = useSnackBar();
+
   const [mutate, { loading, error }] = useMutation<
     CreateEmailGroupChannelResult,
     CreateEmailGroupChannelVariables
@@ -45,7 +48,12 @@ export const useCreateEmailGroupChannel = () => {
   });
 
   const createEmailGroupChannel = (handle: string) =>
-    mutate({ variables: { input: { handle } } });
+    mutate({
+      variables: { input: { handle } },
+      onError: (mutationError) => {
+        enqueueErrorSnackBar({ apolloError: mutationError });
+      },
+    });
 
   return { createEmailGroupChannel, loading, error };
 };