feat: clear the rendered step preview alongside the contact and mailbox picks when the editor changes campaign, so the panel cannot keep showing the previous campaign's sender and attachments while the new render is in flight

web/src/components/app/campaigns/sequences/EmailContentEditor.tsx

@@ -72,12 +72,15 @@ export default function EmailContentEditor({
     // to the campaign's first enabled sender once the pool has loaded.
     const [previewContact, setPreviewContact] = React.useState<Contact | null>(null);
     const [previewMailbox, setPreviewMailbox] = React.useState<Inbox | null>(null);
+    const [serverPreview, setServerPreview] = React.useState<TemplatePreview | null>(null);
     const senders = useCampaignSenderInboxes(campaignId ?? "");
     // Both picks belong to one campaign, so drop them when this editor is
-    // pointed at a different one, or at none, without remounting.
+    // pointed at a different one, or at none, without remounting. The rendered
+    // panel goes with them: it names a sender and files of the old campaign.
     React.useEffect(() => {
         setPreviewContact(null);
         setPreviewMailbox(null);
+        setServerPreview(null);
     }, [campaignId]);
     React.useEffect(() => {
         if (!campaignId) return;
@@ -88,7 +91,6 @@ export default function EmailContentEditor({
 
     const previewMut = useTemplatePreview();
     const runPreview = previewMut.mutateAsync;
-    const [serverPreview, setServerPreview] = React.useState<TemplatePreview | null>(null);
     React.useEffect(() => {
         if (tab !== "preview") return;
         // Responses can land out of order; only the newest request may paint.