Function set_local_string 

pub fn set_local_string(
    adapters_dir: &Path,
    adapter: &str,
    profile: &str,
    key_path: &str,
    value: &str,
) -> Result<(), RegistryError>

Set a [strings] dot-path on a local profile’s overlay — the spt adapter set-string sugar. Edits only the node-local overlay file (profiles/<profile>.toml); a shipped profile name is refused (adapter-owned, immutable) and a missing local profile errors (create-profile first). The edited overlay is re-validated through the same create-time guards (manifest invariants + tighten-only floor) before it is written.