fix(export): stop comment.renderHTML returning a live jsdom node on the server (#298)

Page/space export (Markdown & HTML, both via jsonToHtml -> generateHTML) crashed with
"Export failed:undefined" on any page carrying a `comment` mark. Root cause:
comment.renderHTML returned a LIVE DOM node (document.createElement + a click listener)
whenever a global `document` existed — and the in-process MCP module injects a jsdom
global.window+global.document into the Node server, defeating the old
`typeof document === "undefined"` guard. The server export runs happy-dom's
DOMSerializer, which crashes appending the foreign jsdom node
(NodeUtility.isInclusiveAncestor -> "Cannot read properties of undefined (reading
'length')"). comment is the only extension returning a live node.

Fix: widen the guard with an isNodeRuntime check (process.versions.node) so on any Node
runtime renderHTML returns the plain, serializable spec array — even when MCP injected
jsdom globals. The browser branch (createElement + click -> ACTIVE_COMMENT_EVENT) is
untouched, so in-editor comment interactivity is preserved (Vite defines only
process.env as a member-expression substitution, no `process` object in the browser
bundle, so isNodeRuntime is false there). The mcp schema mirror already returns a spec
array and is not on the export path (tiptapExtensions imports Comment from
@docmost/editor-ext), so no mirror change is needed.

Also: export-modal now reads the real error text from the response Blob
(responseType:'blob' made err.response.data.message always undefined) so a failed export
shows the server's message instead of "undefined".

Adds a regression test that runs the real jsonToHtml on a comment-marked doc with
jsdom globals injected (reproduces the crash on the unpatched code, passes after).

closes #298

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/components/common/export-modal.tsx

@@ -14,6 +14,22 @@ import { notifications } from "@mantine/notifications";
 import { exportSpace } from "@/features/space/services/space-service";
 import { useTranslation } from "react-i18next";
 
+// The export request uses `responseType: "blob"`, so a server error body arrives
+// as a Blob rather than parsed JSON — `err.response?.data.message` is therefore
+// always undefined. Read and parse the blob to surface the real error message.
+async function extractExportError(err: any): Promise<string> {
+  const data = err?.response?.data;
+  if (data instanceof Blob) {
+    try {
+      const json = JSON.parse(await data.text());
+      return json?.message ?? "";
+    } catch {
+      return "";
+    }
+  }
+  return data?.message ?? err?.message ?? "";
+}
+
 interface ExportModalProps {
   id: string;
   type: "space" | "page";
@@ -52,8 +68,9 @@ export default function ExportModal({
       });
       onClose();
     } catch (err) {
+      const message = await extractExportError(err);
       notifications.show({
-        message: "Export failed:" + err.response?.data.message,
+        message: t("Export failed") + (message ? `: ${message}` : ""),
         color: "red",
       });
       console.error("export error", err);