Reload selected settings from environment variables and project files.
This refreshes only fields that are expected to change at runtime
(API keys, Google Cloud project, project root, and LangSmith tracing
project). Resolver-backed configuration is refreshed separately by the
shared ConfigResolver generation.
Runtime model metadata lives in RuntimeState and is never touched by
this method. The original user LangSmith project
(user_langchain_project) is also intentionally preserved because it is
not in _RELOADABLE_FIELDS.
Note
Managed config takes precedence over shell-exported variables for
the fields it declares. Below managed policy, shell exports still
outrank .env values. Values previously injected from .env files
are refreshed so an accepted cwd switch can pick up the resumed
project's .env.
