Function unique_php_call_source 

fn unique_php_call_source(
    graph: &SymbolGraph,
    symbol_index: &GraphSymbolIndex<'_>,
    source_name: &str,
    line: usize,
    control: &IndexWorkControl,
) -> Result<Option<usize>, CliError>

Prefer a proven PHP callable source, falling back to a unique namespace owner.