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export type CopyOnWriteRecord<T> = {

/** The source until the first write, then the one clone every later write reuses. */

read: () => Record<string, T>

/** No-op for an absent key, so deleting nothing never clones. */

delete: (key: string) => void

set: (key: string, value: T) => void

}

/** Clone only on first real write so no-op patches preserve identity-keyed selectors/persist gates. */

export function copyOnWriteRecord<T>(source: Record<string, T>): CopyOnWriteRecord<T> {

let next = source

const mutable = (): Record<string, T> => {

if (next === source) {

next = { ...source }

}

return next

}

return {

read: () => next,

delete: (key) => {

if (key in next) {

delete mutable()[key]

}

set: (key, value) => {

mutable()[key] = value

}