Preview Conversion Tax

Single-year tax preview for a Roth conversion event.

Computes the marginal tax cost of adding amount to the conversion year's taxable ordinary income, using the residency/regime that applies in that year (honoring any relocation events). The baseline reflects the scenario's projected ordinary income (wages, pensions, savings during accumulation) so the preview captures the conversion's marginal bracket impact rather than a stand-alone calculation. The conversion amount is routed as residual ordinary income (matching the engine's tax_deferred_withdrawal lane), which carries the foreign-source tag that the Portugal NHR exemption requires for US citizens abroad.