Refactor medicaid_group to use state-level override pattern for state-funded Medicaid programs

[hua7450]

Problem

PR #7005 (Illinois HBI) adds state-specific logic directly into the federal medicaid_group variable. This approach doesn't scale well - if other states add similar programs (like California FFYP), the federal file will become cluttered with state-specific code.

Current implementation in medicaid_group.py:

# Illinois HBI-specific mapping (for those who fail immigration check
# but are eligible via state-funded HBI program)
il_hbi_eligible = person("il_hbi_eligible", period)
age = person("age", period)
p_hbi = parameters(period).gov.states.il.hfs.hbi.eligibility
il_hbi_child = il_hbi_eligible & (age <= p_hbi.child.max_age)
# ... more Illinois-specific logic

Proposed Solution

Create a generic state override pattern:

1. New file: policyengine_us/variables/gov/states/il/hfs/hbi/il_hbi_medicaid_group.py

   • Returns appropriate MedicaidGroup for HBI-eligible people
   • Returns NONE for everyone else

2. New file: policyengine_us/variables/gov/hhs/medicaid/costs/state_medicaid_group_override.py

   • Aggregates all state-level Medicaid group overrides
   • Future state programs just add their variable to this file

3. Edit: policyengine_us/variables/gov/hhs/medicaid/costs/medicaid_group.py

   • Remove state-specific logic
   • Add generic check for state override at the end:

   state_override = person("state_medicaid_group_override", period)
   has_override = state_override != MedicaidGroup.NONE
   return where(has_override, state_override, federal_group)

Benefits

• Keeps federal variables clean of state-specific logic
• Scales to multiple states without modifying federal files
• State logic stays in state folders (gov/states/il/...)
• Follows existing patterns (similar to how is_medicaid_eligible handles state programs)

Related

• Illinois medicaid for undocumented immigrants #7005 - Illinois Medicaid for undocumented immigrants

[daphnehanse11]

Yes, I wanted to override the whole way we do this a while ago, but we didn't want to change the California system for amplifi which was using the current system. so I've been piecemeal adding the state specific programs, while leaving the federal version intact