scenario_121 encodes disability in inputs PE does not map to USDA disability, zeroing SNAP

Problem

scenario_121 (SC, single 53-year-old) intends a disabled household: the prompt narrates disability, and the inputs set is_disabled: true plus disability_benefits: 13044. But neither input is USDA-qualifying disability under 7 CFR 271.2 (which is receipt-based: SSI, SSDI, VA disability, etc.):

• disability_benefits is PolicyEngine's employer/private disability income variable — not a qualifying federal program
• is_disabled is a bare boolean that PE reads for the SNAP work-registration exemption but not for is_usda_disabled

So the reference pipeline computes a non-disabled SNAP unit: the household fails the 130% gross-income test (ratio 2.55) and gets $0, and the $30k of medical expenses never unlocks the excess-medical deduction. Force is_usda_disabled=true and the same household is eligible with $286/mo ($3,457/yr): elderly/disabled units are exempt from the gross test, and net income collapses to ~$41 after the medical deduction.

The scenario is internally ill-posed rather than PE being wrong — the ground-truth household doesn't represent what the prompt describes. Full trace in PolicyEngine/policybench#91 (row 13).

Options for the next reference refresh

1. Preferred: re-encode the disability as a receipt-based input PE consumes for is_usda_disabled — e.g. route the disability income to social_security_disability (SSDI receipt, SGA-independent). Note the SSI route does not work here: $25,665 wages = $2,139/mo > the 2026 SGA limit.
2. Alternatively, drop the SNAP output for this scenario as a scope gap.

Either changes a frozen scenario/reference, so it belongs in the next snapshot/reference-refresh cycle, not a live patch. Models that treated the household as disabled-for-SNAP and answered a positive amount are currently scored wrong on this cell.

Also worth considering

A generator-side lint: any scenario whose prompt narrates disability should set at least one receipt-based disabled_programs input (is_ssi_disabled chain, social_security_disability, veteran flags), since is_disabled alone propagates inconsistently in policyengine-us (work-registration yes, gross-test exemption no).

Start by tracing scenario_121 and the full trace in PolicyEngine/policybench#91, then inspect how the next snapshot/reference-refresh cycle stores scenario inputs and outputs. Confirm the receipt-based disability input and expected SNAP result against the cited USDA rule; done means the refreshed reference no longer scores the described disabled household as zero, or the SNAP output is removed if that scope gap remains.