Function load_source_map_program 

pub fn load_source_map_program(
    root: &Path,
    contract_name: &str,
    environment: SourceMapEnvironment,
) -> SoldbResult<Option<SourceMapProgram>>

Loads one program from combined.json when the requested source map exists.

Ok(None) means the directory has no legacy artifact, or the selected contract does not contain that creation/runtime map. A present but malformed artifact is always an error so callers cannot silently lose source attribution.