feat: add node startup flow

packages/node/meshnet_node/downloader.py

@@ -0,0 +1,62 @@
+"""Shard downloader — fetches or stubs a model shard from HuggingFace Hub.
+
+Cache layout: ~/.cache/meshnet/shards/<model>/layers_<start>-<end>/
+
+For "stub-model" (no HF repo), a placeholder JSON file is written so the
+test suite never touches the network.
+"""
+
+import json
+from pathlib import Path
+
+_DEFAULT_CACHE = Path.home() / ".cache" / "meshnet" / "shards"
+
+
+def download_shard(
+    model: str,
+    shard_start: int,
+    shard_end: int,
+    cache_dir: Path = _DEFAULT_CACHE,
+    hf_repo: str | None = None,
+    progress: bool = True,
+) -> Path:
+    """Ensure the shard is present in *cache_dir* and return its local path.
+
+    When *hf_repo* is None (or *model* is ``"stub-model"``), a placeholder
+    weights file is created locally — no network access required.  This keeps
+    the test suite hermetic while the real download path is exercised by
+    passing a non-stub *hf_repo*.
+    """
+    shard_dir = cache_dir / model / f"layers_{shard_start}-{shard_end}"
+    shard_dir.mkdir(parents=True, exist_ok=True)
+
+    if hf_repo is None or model == "stub-model":
+        stub_file = shard_dir / "weights.json"
+        if not stub_file.exists():
+            stub_file.write_text(json.dumps({
+                "model": model,
+                "shard_start": shard_start,
+                "shard_end": shard_end,
+                "stub": True,
+            }))
+            if progress:
+                print(f"  [stub] shard placeholder written to {stub_file}", flush=True)
+        else:
+            if progress:
+                print(f"  [stub] shard already cached at {shard_dir}", flush=True)
+        return shard_dir
+
+    from huggingface_hub import snapshot_download  # type: ignore[import]
+
+    if progress:
+        print(
+            f"  Downloading layers {shard_start}-{shard_end} from {hf_repo} ...",
+            flush=True,
+        )
+
+    local_dir = snapshot_download(
+        repo_id=hf_repo,
+        cache_dir=str(cache_dir),
+        local_dir=str(shard_dir),
+    )
+    return Path(local_dir)