I have an edit state that returns an edit for a single key out of many.

type EditState_Empty = {
    name: null
    value: null
}

type EditState_InProgress = {
    name: 'name1' | 'name2'
    value: string
}

type EditState = EditState_Empty | EditState_InProgress

type AfterEditParams = {name1: string} | {name2: string}

const initialState = {
    name: null, value: null
}
const reducer = (prev: EditState, action: string): EditState => {
    switch (action) {
        case 'name1':
            return {
                name: 'name1',
                value: 'some-value'
            } as const
        case 'name2':
            return {
                name: 'name2',
                value: 'some-value'
            } as const
        default:
            return initialState
    }

}

const saveEdit = (editState: EditState_InProgress): void => {
    const editParam: AfterEditParams = {
        [editState.name]: editState.value,
    } as const
}

TypeScript tells me:

Type '{ readonly [x: string]: string; }' is not assignable to type 'AfterEditParams'.
  Property 'name2' is missing in type '{ readonly [x: string]: string; }' but required in type '{ name2: string; }'.

Here is the example on TypeScript playground:

Will someone please explain why the error occurs and how to fix it?