* fix(gateway): answer malformed run bodies with 4xx instead of 500
RunCreateRequest types config, context and input as free-form dicts, so
some bodies it accepts still failed during run admission with an
exception nothing mapped, and the run routes answered 500:
- a non-object config.configurable (build_run_config's dict.update, and
.get in the stateless thread selector)
- a non-object config.context (build_run_config's own ValueError)
- an assistant_id that does not normalize to letters, digits and hyphens
- a non-string agent_name in config.configurable, config.context or
context (_load_scope_agent_config)
- an AI message whose tool_calls is a string, object or list of strings
(AttributeError from LangChain's validator)
The request model now requires config.configurable and config.context to
be objects or null (422 invalid_run_config_section), and
build_run_config checks configurable as it already checked context.
start_run maps build_run_config's ValueError to 422, as it does for
validate_thread_id. Message conversion also maps AttributeError to its
existing 400, and a non-string agent_name gets the existing 422 for an
unresolvable agent. All of these fail before admission, so no run is
created.
* docs(changelog): reference #7362 for the malformed run body fix
* docs(changelog): note the configurable shapes #7362 now rejects
5bda01f524