fix(vm_provision_mixin): write Cloud-Init snippet via SSH, not the upload API

Real Proxmox's POST /nodes/{node}/storage/{storage}/upload only accepts
content in {iso, vztmpl, import} — content='snippets' is rejected
outright with a 400 ("does not have a value in the enumeration").
Snippets can only be written directly to the storage's filesystem path.

Found live, right after the previous multipart-upload fix: the VM
shell, disk import, and node-scoped storage selection all succeeded,
then create_vm_from_cloud_init failed with a 400 at the snippet write
step. Resolves the storage's path via the cluster storage config and
writes the file over SSH (base64-piped, to survive arbitrary YAML
content safely).

napalm_proxmox/vm_provision_mixin.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-import io
+import base64
 import logging
 import time
 import yaml
@@ -130,6 +130,25 @@ class ProxmoxVMProvisionMixin:
             "No storage with content='images' found. Configure a storage for VM disks."
         )
 
+    def _get_storage_path(self, storage: str) -> str:
+        """Resolve a storage's filesystem path on the node.
+
+        Needed to write Cloud-Init snippets directly: Proxmox's
+        /storage/{s}/upload API only accepts content in {iso, vztmpl,
+        import} — "snippets" is rejected outright, so snippets must be
+        written straight to the filesystem instead. Only dir-backed storages
+        (dir, nfs, cifs, cephfs) expose "path"; those are also the only
+        storage types Proxmox itself allows content='snippets' on.
+        """
+        config = self._api.storage(storage).get()
+        path = config.get("path")
+        if not path:
+            raise ValueError(
+                f"Storage '{storage}' has no filesystem path (content='snippets' "
+                "requires a dir/nfs/cifs/cephfs-backed storage)"
+            )
+        return path
+
     def get_image_storages(self) -> List[StorageTargetDict]:
         """List node-available storage pools suitable for a new VM's root disk."""
         targets: List[StorageTargetDict] = []
@@ -336,20 +355,19 @@ class ProxmoxVMProvisionMixin:
             )
 
             filename = f"{vmid}-user-data.yaml"
-            _logger.debug(f"Uploading Cloud-Init snippet {filename} to {snippet_storage}")
+            _logger.debug(f"Writing Cloud-Init snippet {filename} to {snippet_storage}")
 
-            # Upload to snippet storage. Proxmox's upload endpoint expects the
-            # "filename" parameter to BE the file (multipart), not a name
-            # string with separate content — proxmoxer only builds a
-            # multipart request when the value is an io.IOBase instance,
-            # otherwise it silently sends everything as a plain
-            # form-urlencoded POST, which real Proxmox rejects by dropping
-            # the connection (RemoteDisconnected, no HTTP response at all).
-            file_obj = io.BytesIO(user_data_yaml.encode("utf-8"))
-            file_obj.name = filename
-            self._node_api().storage(snippet_storage).upload.post(
-                content="snippets",
-                filename=file_obj,
+            # Proxmox's /storage/{s}/upload API only accepts content in
+            # {iso, vztmpl, import} — "snippets" is rejected outright
+            # ("does not have a value in the enumeration"). Snippets can only
+            # be written directly to the filesystem, so resolve the storage's
+            # backing path and write the file over SSH instead.
+            storage_path = self._get_storage_path(snippet_storage)
+            encoded = base64.b64encode(user_data_yaml.encode("utf-8")).decode("ascii")
+            self._run_node_command(
+                f"mkdir -p {storage_path}/snippets && "
+                f"echo {encoded} | base64 -d > {storage_path}/snippets/{filename}",
+                timeout=30,
             )
 
             # Step 7: Configure Cloud-Init references and SSH keys