fix: refine mail export and mailbox deletion

apps/api/internal/app/mailbox_delete_test.go

@@ -0,0 +1,34 @@
+package app
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestAdminCanDeleteOwnLastMailboxWithoutDeletingAccount(t *testing.T) {
+	a := newTestApp(t)
+	ts := httptest.NewServer(a.Router())
+	defer ts.Close()
+	admin := &testClient{t: t, server: ts}
+	var login map[string]any
+	if code := admin.do("POST", "/api/auth/login", map[string]string{"email": "admin@lanqin.local", "password": "ChangeMe123!"}, &login); code != http.StatusOK {
+		t.Fatalf("admin login=%d", code)
+	}
+	var mailboxes struct {
+		Items []Mailbox `json:"items"`
+	}
+	if code := admin.do("GET", "/api/mail/mailboxes", nil, &mailboxes); code != http.StatusOK || len(mailboxes.Items) != 1 {
+		t.Fatalf("mailboxes code=%d items=%d", code, len(mailboxes.Items))
+	}
+	if code := admin.do("DELETE", "/api/admin/mailboxes/"+mailboxes.Items[0].ID, nil, &map[string]any{}); code != http.StatusOK {
+		t.Fatalf("delete final mailbox code=%d", code)
+	}
+	if code := admin.do("GET", "/api/mail/mailboxes", nil, &mailboxes); code != http.StatusOK || len(mailboxes.Items) != 0 {
+		t.Fatalf("mailboxes after delete code=%d items=%d", code, len(mailboxes.Items))
+	}
+	var me map[string]any
+	if code := admin.do("GET", "/api/me", nil, &me); code != http.StatusOK {
+		t.Fatalf("account was not preserved code=%d", code)
+	}
+}