Add automatic CUA_API_KEY environment variable support for Computer and CloudProvider

Previously, users had to explicitly read the CUA_API_KEY environment variable
and pass it to the Computer/CloudProvider constructor. This change makes the
API key parameter optional and automatically reads from the CUA_API_KEY
environment variable if not provided.

Changes:
- CloudProvider.__init__: Made api_key parameter optional, reads from CUA_API_KEY env var
- Computer.__init__: Added fallback to CUA_API_KEY env var for api_key parameter
- Updated documentation examples to show simplified usage without explicit api_key
- Updated cloud_api_examples.py to demonstrate the new simpler pattern

This provides a cleaner API while maintaining backward compatibility with
explicit api_key parameter passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

libs/python/computer/computer/computer.py

@@ -98,13 +98,17 @@ class Computer:
             host: Host to use for VM provider connections (e.g. "localhost", "host.docker.internal")
             storage: Optional path for persistent VM storage (Lumier provider)
             ephemeral: Whether to use ephemeral storage
-            api_key: Optional API key for cloud providers
+            api_key: Optional API key for cloud providers (defaults to CUA_API_KEY environment variable)
             experiments: Optional list of experimental features to enable (e.g. ["app-use"])
         """
 
         self.logger = Logger("computer", verbosity)
         self.logger.info("Initializing Computer...")
 
+        # Fall back to environment variable for api_key if not provided
+        if api_key is None:
+            api_key = os.environ.get("CUA_API_KEY")
+
         if not image:
             if os_type == "macos":
                 image = "macos-sequoia-cua:latest"

libs/python/computer/computer/providers/cloud/provider.py

@@ -31,18 +31,21 @@ class CloudProvider(BaseVMProvider):
 
     def __init__(
         self,
-        api_key: str,
+        api_key: Optional[str] = None,
         verbose: bool = False,
         api_base: Optional[str] = None,
         **kwargs,
     ):
         """
         Args:
-            api_key: API key for authentication
+            api_key: API key for authentication (defaults to CUA_API_KEY environment variable)
             name: Name of the VM
             verbose: Enable verbose logging
         """
-        assert api_key, "api_key required for CloudProvider"
+        # Fall back to environment variable if api_key not provided
+        if api_key is None:
+            api_key = os.getenv("CUA_API_KEY")
+        assert api_key, "api_key required for CloudProvider (provide via parameter or CUA_API_KEY environment variable)"
         self.api_key = api_key
         self.verbose = verbose
         self.api_base = (api_base or DEFAULT_API_BASE).rstrip("/")