Module hk 

Henry-Kafura coupling over flow edges. For each internal (non-external) node we count unique flow partners (fan_in / fan_out), track outgoing edges to external libraries separately (fan_out_external), and compute hk = sloc · (fan_in · fan_out)². Results are written into node attrs as flat keys; zero values are omitted.

Functions

annotate_hk

Annotate fan_in / fan_out / fan_out_external / hk on every internal node, counting only flow edges. External nodes carry no coupling metrics.