ACA applicable percentage uses the contiguous-states poverty guideline for Alaska and Hawaii

**Observed** (API, 2026): a single 30-year-old in Alaska with `tax_unit_is_filer: true` on an `employment_income` axis $60,000–$80,000:

| MAGI | `tax_unit_fpg` | `aca_magi_fraction` | implied denominator | `premium_tax_credit` |
|---|---|---|---|---|
| $61,000 | $19,950 | 3.89 | $15,681 | $4,838 |
| $66,000 | $19,950 | 4.21 | $15,677 | $0 |
| $71,000 | $19,950 | 4.53 | $15,673 | $0 |

`tax_unit_fpg` correctly reports Alaska's guideline, but `aca_magi_fraction` divides MAGI by ≈ $15,650 — the 2025 guideline for the 48 contiguous states — so the credit ends at 4 × $15,650 = $62,600 of MAGI instead of 4 × $19,550 (Alaska's 2025 one-person guideline) = $78,200. Hawaii shows the same pattern (its own guideline reported, fraction on the contiguous figure). The vintage (2025, per 26 CFR 1.36B-1(h)) is right; the geography is not.

**Expected**: the ACA applicable-percentage and 400% cap should use the Alaska and Hawaii guidelines for households in those states. Roughly $16,600 of earnings early for an Alaska single, ~$8,300 for Hawaii.

**Repro**: the household above, `state_name: AK`, requesting `aca_magi`, `aca_magi_fraction`, `tax_unit_fpg`, `premium_tax_credit`.

Start from the API calculations for aca_magi_fraction, tax_unit_fpg, and premium_tax_credit, reproducing the Alaska household described in the issue and comparing it with Hawaii. Trace how the applicable percentage selects its poverty-guideline denominator; done means Alaska and Hawaii use their state guidelines for the fraction and 400% cap while the existing 2025 vintage remains unchanged.

Written by the indexing model from the issue text.