Model Medicaid community engagement verification and review-period mechanics

## Summary

The June 1, 2026 CMS interim final rule includes detailed application, renewal, review-period, verification, notice, and implementation mechanics for Medicaid community engagement. PolicyEngine currently applies the community engagement condition through annual eligibility logic and does not model the administrative timing details.

## Sources

- CMS fact sheet: https://www.cms.gov/newsroom/fact-sheets/medicaid-community-engagement-requirement-certain-individuals-interim-final-rule-comment-period-cms
- IFC text: https://public-inspection.federalregister.gov/2026-11094.pdf
- Current variables: `policyengine_us/variables/gov/hhs/medicaid/eligibility/is_medicaid_eligible.py`, `policyengine_us/variables/gov/hhs/medicaid/eligibility/medicaid_work_requirement_eligible.py`

## Policy Details

The IFC states that the regulations are effective July 31, 2026, with implementation required no later than January 1, 2027, subject to good faith effort exemptions. At application, states must require demonstration for at least one and not more than three consecutive months immediately preceding application. At renewal, states must verify one or more months during the review period, with more frequent verification optional. The rule also requires checking reliable information before requesting documentation, gives a 30-calendar-day opportunity to respond to noncompliance notices, and interacts with six-month adult-group renewals.

## Proposed Modeling Work

Decide how much of the administrative process should be represented in PolicyEngine versus documented as outside model scope. Potential parameters include implementation date, good faith exemption status, months required at application, months required at renewal, and whether a state verifies more frequently than renewal. Potential variables could distinguish eligibility-rule failure from procedural disenrollment risk.

## Acceptance Criteria

- The repo has an explicit model or documented non-modeling decision for application review periods, renewal review periods, implementation timing, and good faith exemptions.
- If modeled, state parameters and tests cover one-month versus multi-month review requirements.
- If modeled, tests cover implementation-date behavior for 2026 and 2027.
- Any procedural disenrollment approximation is separated from substantive eligibility where feasible.