feat: implement session management and terminal handling with UI updates and backend support

uvm/images.py

@@ -89,6 +89,11 @@ check_python
 """
 
 
+# The original v4 template shipped this exact agent without an ownership
+# manifest. Recognize that payload when creating from a cached v4 template.
+_V4_TEMPLATE_AGENT_SHA256 = "dfdd4bd6ee3dc06fbdbda6402cb2c54921cff22190d8da889209559800f8b948"
+
+
 def guest_agent_files() -> dict[str, bytes]:
     """The same standalone payload is used by the builder and offline upgrades."""
     return {
@@ -283,7 +288,7 @@ class ImageStore:
         )
         if marker is None or marker.path.read_text(encoding="utf-8") not in {
             "uvm-ubuntu-jammy-v1\n", "uvm-ubuntu-jammy-v2\n", "uvm-ubuntu-jammy-v3\n",
-            "uvm-ubuntu-jammy-v4\n",
+            "uvm-ubuntu-jammy-v4\n", "uvm-ubuntu-jammy-v5\n",
         }:
             return None
         profile = self._read_guest_file(
@@ -374,7 +379,10 @@ class ImageStore:
             existing = self._agent_file(disk, path, files / f"existing-{index}")
             if existing is not None:
                 digest = hashlib.sha256(existing.path.read_bytes()).hexdigest()
-                if digest not in {hashes[path], old_hashes.get(path)}:
+                allowed = {hashes[path], old_hashes.get(path)}
+                if not old_hashes and path == "/usr/lib/uvm/agent.py":
+                    allowed.add(_V4_TEMPLATE_AGENT_SHA256)
+                if digest not in allowed:
                     raise UvmError(f"refusing to overwrite a customized guest agent file: {path}")
             source = files / f"payload-{index}"
             source.write_bytes(content)