Carry SNAP reported amounts and take-up inputs through Populace US outputs

[daphnehanse11]

Parent: #248

Problem

Populace US does not currently expose the SNAP reported amount or SNAP take-up input that policyengine-us-data carried through for microsimulation.

In PolicyEngine-US:

• snap_reported is an SPM-unit input used when gov.simulation.reported_snap is enabled.
• takes_up_snap_if_eligible gates simulated SNAP benefits in microsimulation mode.
• takes_up_snap_if_eligible defaults to True, so when it is absent, every eligible SPM unit is treated as taking up SNAP.

The current Populace H5 has raw CPS/SPM SPM_SNAPSUB on the person table, but does not expose:

• snap_reported
• takes_up_snap_if_eligible

This is a material parity gap with policyengine-us-data, especially for SNAP enrollment/distribution analysis and OBBBA SNAP work-requirement exposure.

Evidence

Legacy policyengine-us-data:

• maps snap_reported = SPM_SNAPSUB in add_spm_variables;
• creates takes_up_snap_if_eligible in add_takeup;
• prioritizes reported SNAP recipients when assigning the take-up indicator.

On the local legacy enhanced_cps_2024.h5 snapshot:

• snap_reported is present on SPM units;
• takes_up_snap_if_eligible is present on SPM units;
• weighted reported SNAP receipt is not universal, and the take-up flag is not all true.

On the Populace 2024 H5 used in the SNAP audit:

• raw SPM_SNAPSUB is present;
• snap_reported is absent;
• takes_up_snap_if_eligible is absent.

Proposed Scope

1. Aggregate raw SPM_SNAPSUB to the PolicyEngine SPM-unit grain and expose it as snap_reported.
2. Add a Populace-owned takes_up_snap_if_eligible assignment.
3. Preserve reported SNAP recipients as true anchors where possible.
4. Use the same deterministic/stable-random pattern used for other Populace take-up assignments.
5. Add diagnostics comparing:
   • reported SNAP SPM units / households,
   • simulated eligible units,
   • take-up units,
   • final SNAP recipients and spending.

Acceptance Criteria

• snap_reported exists in the Populace US output at SPM-unit grain.
• takes_up_snap_if_eligible exists in the Populace US output at SPM-unit grain.
• The take-up flag is not a degenerate all-true default.
• Reported SNAP recipients are preserved as take-up recipients unless explicitly documented otherwise.
• Tests cover schema presence, deterministic assignment, and non-degenerate weighted take-up distribution.

Related

• Carry hours-worked inputs through Populace US outputs #242 tracks hours worked, another SNAP work-requirement blocker.
• [codex] Add SNAP local proxy diagnostics scaffold #241 adds validation-only SNAP local proxy diagnostics, but does not populate these model inputs.