fix(git-sync): forward gzip encoding (#4) + catch read-advertise reject after hijack (#5); fix Export 500 on pages with inline comments

- Review #4: forward HTTP_CONTENT_ENCODING to git http-backend so it inflates
  gzip'd RPC bodies — a non-trivial `git pull` no longer fails with
  `fatal: expected 'packfile'`. (git-http-backend + git-http.service)
- Review #5: the read-advertisement branch runs under the space lock AFTER
  reply.hijack(); a reject there (e.g. Redis down) previously left the socket
  open forever, hanging every clone/fetch. Mirror the push branch: catch, 500 if
  unwritten, always end the socket. (git-http.service)
- GS-EXPORT-500 (QA): a page with an inline comment mark returned HTTP 500 on
  Export/copy-as-markdown. The Comment mark's renderHTML took the imperative
  document.createElement branch server-side (the DOM shim used by generateHTML
  defines window/document), returning a live node with no content hole that
  crashed prosemirror-model's DOMSerializer under happy-dom. Gate the imperative
  branch on a real browser (navigator.userAgent contains 'Mozilla'); the server
  now uses the static DOMOutputSpec form. Verified: export 200 (was 500).

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

packages/editor-ext/src/lib/comment/comment.ts

@@ -172,7 +172,27 @@ export const Comment = Mark.create<ICommentOptions, ICommentStorage>({
     const commentId = HTMLAttributes?.["data-comment-id"] || null;
     const resolved = HTMLAttributes?.["data-resolved"] || false;
 
-    if (typeof window === "undefined" || typeof document === "undefined") {
+    // Prefer the static array (DOMOutputSpec) form whenever we are NOT in a real
+    // interactive browser. Guarding only on `document`/`window` is insufficient
+    // on the server: `generateHTML()` runs under a DOM shim (happy-dom/jsdom) that
+    // DEFINES both globals, so the imperative `document.createElement` branch ran
+    // server-side and its live node + addEventListener crashed the shim's
+    // DOMSerializer ("Cannot read properties of undefined (reading 'length')"),
+    // turning every Export / copy-as-markdown of a page with an inline comment
+    // into an HTTP 500 (QA GS-EXPORT-500). A real browser has a non-empty
+    // navigator.userAgent; the SSR shims do not — route the server to the safe
+    // static form while keeping the clickable node in the actual editor.
+    const isInteractiveBrowser =
+      typeof window !== "undefined" &&
+      typeof document !== "undefined" &&
+      typeof navigator !== "undefined" &&
+      typeof navigator.userAgent === "string" &&
+      // Real browsers ALL carry "Mozilla" in the UA string (historical); the
+      // server-side DOM shim used by generateHTML() does not (e.g. "Node.js/22").
+      // This keeps the interactive click node ONLY in a true browser and routes
+      // the server to the crash-free static form.
+      navigator.userAgent.includes("Mozilla");
+    if (!isInteractiveBrowser) {
       return [
         "span",
         mergeAttributes(this.options.HTMLAttributes, HTMLAttributes, {