Function set_explicit_config_path 

pub fn set_explicit_config_path(path: Option<PathBuf>)

Capture the session’s explicit config-file override.

Called during startup after the CLI/env path has been resolved to an absolute file path. Passing None clears the override and invalidates the workspace config cache so subsequent loads return to the default layer hierarchy instead of a stale override-loaded manager.

This is process-global and intended to be set once per process at startup; changing it mid-session is supported for tests and reloads, but consumers must not race concurrent calls.