Function summarize_function 

pub fn summarize_function(
    fn_ast_in: &str,
    callgraph_in: &str,
    cached_summary_in: &str,
    summary_out: &str,
) -> Program

One summary-update step for a single function.

Bit i of summary_out is set iff any of: the AST-derived bit was set, the callgraph-aggregated bit from callee summaries was set, or the cached summary from the previous scan was set. That is a three-way OR - same kernel shape as escape, different buffer names.