docs: add gotcha about hf.co vs huggingface.co for git ops

AGENTS.md

@@ -426,3 +426,22 @@ ValueError: A function didn't return enough output values (needed: N, returned:
 ```
 
 This applies to all generator click/change handlers in `frontend/ui/widgets.py:build_ui()`.
+
+### 13. Hugging Face git hostname is `hf.co`, not `huggingface.co`
+
+For **git operations** (push/pull/fetch) with Hugging Face Spaces, use `git@hf.co:user/repo.git` — **not** `git@huggingface.co:user/repo.git`. The two hostnames resolve differently:
+- `hf.co` → correct git SSH endpoint (returns `Hi <user>, welcome to Hugging Face.`)
+- `huggingface.co` → web frontend; SSH connection times out or returns `Host key verification failed`
+
+The **web URL** still uses `huggingface.co/spaces/...`. Never mix the two:
+
+```bash
+# ✅ Correct — git operations use hf.co
+git remote set-url hf git@hf.co:build-small-hackathon/EuropaLex.git
+git push hf main
+
+# ❌ Wrong — huggingface.co for git hangs/times out
+git remote set-url hf git@huggingface.co:build-small-hackathon/EuropaLex.git
+```
+
+For **HTTPS** pushes, use `https://<TOKEN>@huggingface.co/...` (the web hostname is fine for token-based auth). For **SSH**, always use `hf.co`. Binary files (test outputs like `.wav`, `.png`) are rejected by HF's git hook — exclude them in `.gitignore` and run `git filter-branch` on existing history if they were already committed.