Review found the suffix-set match alone is unsafe: revenue-side recipes
(ig_federal_b47_wide, ig_state_c47_wide, ig_local_d47_wide, and their *_89
siblings) coincidentally share exact suffix sets with M/L expenditure
recipes despite representing a different flow direction. Reachable today via
a mis-scoped cog_spending(category = "IG Federal") call, not just
cog_revenue(). Thread flow_prefixes (same parameter .build_harmonization_block
already uses) through .build_suggestions()/.attach_ig_counterparts() and
require a firing recipe's own prefixes to be both in the calling verb's flow
family and within {E,F,G} before searching the M/L catalog.