Model Rhode Island Ticket to Work and Sherlock as separate Medicaid buy-in pathways

Follow-up to #8493 and narrower successor to closed #8481. Rhode Island should be modeled separately, or at least as named subpathways behind the shared working-disabled buy-in category, because the current program is not one flat buy-in rule.

## Why this is separate from the shared schema

Rhode Island's current public EOHHS materials split Medicaid Programs for Working People with Disabilities into two named pathways:

- Ticket to Work (TTW), ages 16-64.
- Sherlock Plan, age 65 and older.

Those two pathways have different financial limits and premium schedules:

- TTW has no income limit and no asset limit.
- Sherlock has a 250% FPL income limit and a $10,000 individual / $20,000 couple asset limit.
- TTW premiums continue well above 250% FPL.
- Sherlock premiums only apply across the lower schedule up to its 250% FPL income limit.
- EOHHS says Sherlock participants as of September 2024 were automatically transitioned into TTW, and people in TTW nearing age 65 are evaluated for Sherlock after turning 65.

That is more than ordinary parameter variation. A single `age/min`, `age/max`, `income_limit`, and `asset_limit` row cannot represent both pathways without either losing the TTW no-limit rule or losing the Sherlock age-65+ rule.

## Source details

Rhode Island EOHHS page, last updated April 28, 2026:

- Programs for working people with disabilities are:
- Ticket to Work, ages 16-64.
- Sherlock Plan, ages 65+.
- Both provide full Medicaid medical benefits, HCBS/LTSS where applicable, and services needed to start or continue employment.
- TTW eligibility:
- age 16-64 inclusive;
- meet Medicaid disability requirements;
- disability does not require inability to work;
- proof of active paid employment;
- no income limit;
- no asset limit;
- premiums based on FPL.
- TTW premium schedule:
- 0 to <150% FPL: no premium;
- 150 to <185% FPL: $61;
- 185 to <200% FPL: $77;
- 200 to <250% FPL: $92;
- then increasing brackets through 900%+ FPL, with $370 at 900%+ FPL.
- Sherlock eligibility:
- age 65 or older;
- meet Medicaid disability requirements;
- proof of active paid employment;
- countable earned net income no greater than 250% FPL after SSI-related disregards;
- countable assets no greater than $10,000 individual / $20,000 couple;
- medical savings accounts, retirement accounts, and approved work-related items are excluded.
- Sherlock premium schedule:
- 0 to <150% FPL: no premium;
- 150 to <185% FPL: $61;
- 185 to <200% FPL: $77;
- 200 to <250% FPL: $92.

Rhode Island's administrative rule also describes the Sherlock Plan as an SSI-related eligibility pathway for working adults with disabilities and distinguishes non-LTSS coverage from LTSS coverage. That adds another reason to avoid flattening the Rhode Island rules into one generic row before checking how to handle LTSS and cost sharing.

## Implementation notes

- Create Rhode Island-specific variables or subpathway parameters for TTW and Sherlock rather than one state row.
- Feed both subpathways into the shared `WORKING_DISABLED_BUY_IN` category from #8493.
- Represent TTW no-income/no-asset limits explicitly instead of treating missing limits as unavailable coverage.
- Represent Sherlock income and asset limits separately from TTW.
- Add a premium table that can support TTW's extended brackets above 250% FPL.
- Verify whether LTSS Sherlock cost-sharing should be modeled in this issue or deferred to a separate LTSS/cost-sharing issue.
- Note the apparent source/version issue: the current EOHHS consumer page presents TTW as 16-64 and Sherlock as 65+, while older regulatory language describes Sherlock more broadly. The implementation should rely on current controlling authority and document the date/source used.

## Acceptance criteria

- A disabled Rhode Island worker age 16-64 with paid employment qualifies through TTW even when income/assets exceed the Sherlock limits.
- A disabled Rhode Island worker age 65+ with paid employment qualifies through Sherlock only if they meet the Sherlock income and asset tests.
- TTW and Sherlock both map to the shared working-disabled buy-in Medicaid category.
- TTW premiums are computed beyond 250% FPL using the Rhode Island schedule.
- Sherlock premiums stop at the schedule relevant to its 250% FPL income limit.
- Tests cover a 64-year-old TTW case, a 65-year-old Sherlock case, and a high-income TTW case with a premium above the Sherlock maximum.

## Sources

- Rhode Island EOHHS, Medicaid Programs For Working People With Disabilities: https://eohhs.ri.gov/Consumer/TheSherlockPlan.aspx
- Stay Covered Rhode Island, Adults With Disabilities: https://staycovered.ri.gov/your-medicaid-benefits/programs-services/adults-disabilities
- Rhode Island Department of State, 210-RICR-40-15-1, Medicaid for Working People with Disabilities Program: https://rules.sos.ri.gov/Regulations/part/210-40-15-1?reg_id=10076
- Sherlock Center on Disabilities, New expansion to Medicaid buy-in removes limits for workers with disabilities: https://sherlockcenter.ric.edu/news-stories/new-expansion-medicaid-buy-removes-limits-workers-disabilities

Related: #8493, #8481, #8102, #8497.