[codex] Refresh HBAI columns after structural post-hooks

[nikhilwoodruff]

What changed

This refreshes derived household HBAI columns inside the Python aggregate_microdata() path before poverty metrics are calculated. In particular, it recomputes *_net_income_ahc, *_equivalised_net_income, and *_equivalised_net_income_ahc from household net income, housing costs, and equivalisation factors.

Why

Structural post-hooks can mutate household net income directly. Before this change, the Python aggregation layer trusted the pre-hook-derived HBAI columns already present on the household dataframe, so post-hooks could leave AHC and equivalised values stale. That made poverty outputs unreliable for household-level cash-transfer style reforms.

Impact

Household-level structural post-hooks now produce poverty results that stay consistent with the modified net incomes, without requiring each hook to manually update every derived HBAI field.

Validation

• python -m compileall interfaces/python/policyengine_uk_compiled/structural.py
• Reproduced the bug in the local checkout with a post-hook that only increments reform_net_income, then confirmed the patched aggregation produced sensible BHC and AHC poverty movement.