Parsing for the [sandboxes] section of ~/.deepagents/config.toml.
Parallels the [models] provider configuration in model_config.py. Config
providers declare a class_path (same trust model as model class_path),
a working_dir, an optional install package, and params forwarded to
provider.get_or_create().
Configuration for a single config-declared sandbox provider.
Warning
Setting class_path executes arbitrary Python code imported from the
user's config file. This has the same trust model as model
class_path — the user controls their own machine.
Parsed [sandboxes] configuration from config.toml.
Instances are immutable once constructed; providers is wrapped in a
MappingProxyType to prevent accidental mutation.