[codex] Integrate household costs into cliff reporting

[daphnehanse11]

Summary

This PR finishes the household-cost integration that started with CHIP premiums.

It updates both the browser-side PolicyEngine path and the Python calculator path so household costs are treated consistently in net resource calculations, cliff drivers, and the chart UI.

What changed

• subtract chip_premium from net_resources in the browser-side PolicyEngine transformer for both household and series results
• request chip_premium from the browser-side PolicyEngine situation payload and carry it through the returned result shape
• include household cost increases in cliff-driver generation in both the frontend and Python calculator paths
• preserve those drivers during refined-series recomputation so cliff explanations stay accurate after zooming into cliff zones
• render household costs in the detail chart using metadata.household_costs, including CHIP premium as a visible negative series and as a tooltip row in net-income mode
• update cliff-report copy so it reflects household cost increases as reportable drivers
• add focused tests for the frontend PolicyEngine transformer and Python cliff-driver logic

Why

Max's package refactor correctly introduced household costs on the Python side, but the app still had three integration gaps:

• the browser-side calculation path ignored CHIP premiums in net_resources
• cliff explanations never attributed drops to household cost increases
• the UI had no place to show household costs even when the backend exposed them

That meant the app could miss real CHIP-premium cliffs in normal usage and under-explain them even when they were present.

Impact

Users now see household costs reflected consistently in:

• net income calculations
• cliff-driver explanations
• the detail chart and tooltip breakdowns

This keeps the browser path, fallback API path, and visual explanations aligned.

Validation

• uv run pytest
• npm test
• npm run build

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Project	Deployment	Actions	Updated (UTC)
cliff-watch	Ready	Preview, Comment	Apr 20, 2026 8:35pm