Fix push preview JMAP query

Resolve the Inbox mailbox id before running Email/query.

The previous query passed a JMAP result reference object directly into the inMailbox filter, which can make the preview endpoint return 502 and cause push notifications to fall back to the generic “New mail” text.

app/api/push/preview/route.ts

@@ -40,17 +40,53 @@ export async function GET(request: NextRequest) {
       return NextResponse.json({ error: 'Incomplete JMAP session' }, { status: 502 });
     }
 
-    // Find the inbox, then pull the most recent unread message in it. We use
-    // a single batched JMAP request with back-references so this round-trip
-    // is one POST regardless of how many messages exist.
+    const inboxRes = await fetch(apiUrl, {
+      method: 'POST',
+      headers: {
+        Authorization: creds.authHeader,
+        'Content-Type': 'application/json',
+      },
+      body: JSON.stringify({
+        using: ['urn:ietf:params:jmap:core', 'urn:ietf:params:jmap:mail'],
+        methodCalls: [
+          [
+            'Mailbox/query',
+            { accountId, filter: { role: 'inbox' }, limit: 1 },
+            'mb',
+          ],
+        ],
+      }),
+    });
+
+    if (!inboxRes.ok) {
+      return NextResponse.json({ error: 'JMAP mailbox query failed' }, { status: 502 });
+    }
+
+    const inboxData = (await inboxRes.json()) as {
+      methodResponses: [string, Record<string, unknown>, string][];
+    };
+
+    const inboxBody = inboxData.methodResponses.find(
+      ([method]) => method === 'Mailbox/query',
+    )?.[1] as { ids?: string[] } | undefined;
+
+    const inboxId = inboxBody?.ids?.[0];
+
+    if (!inboxId) {
+      return NextResponse.json({
+        email: null,
+        unreadTotal: 0,
+      }, {
+        headers: {
+          'Cache-Control': 'no-store',
+        },
+      });
+    }
+
+    // Pull the most recent unread message from the resolved Inbox mailbox.
     const requestBody = {
       using: ['urn:ietf:params:jmap:core', 'urn:ietf:params:jmap:mail'],
       methodCalls: [
-        [
-          'Mailbox/query',
-          { accountId, filter: { role: 'inbox' }, limit: 1 },
-          'mb',
-        ],
         [
           'Email/query',
           {
@@ -58,7 +94,7 @@ export async function GET(request: NextRequest) {
             filter: {
               operator: 'AND',
               conditions: [
-                { inMailbox: { resultOf: 'mb', name: 'Mailbox/query', path: '/ids/0' } },
+                { inMailbox: inboxId },
                 { notKeyword: '$seen' },
               ],
             },