fix: handle nested proxies after spreading and inserting into an array

__tests__/base.js

@@ -2778,6 +2778,53 @@ function runBaseTest(
 			expect(nextState).toEqual({foo: {bar: {a: true, c: true}}})
 		})
 
+		// #1209 - spread draft object and push back via array methods
+		it("can spread a draft and push it back into the array", () => {
+			const base = [{nestedArray: []}]
+			const next = produce(base, s => {
+				s.push({...s[0]})
+			})
+			expect(next[0].nestedArray).toEqual([])
+			expect(next[1].nestedArray).toEqual([])
+			expect(next[1].nestedArray.length).toBe(0)
+		})
+
+		it("can spread a draft with nested objects and push it back", () => {
+			const base = [{nested: {value: 42}}]
+			const next = produce(base, s => {
+				s.push({...s[0]})
+			})
+			expect(next[0].nested.value).toBe(42)
+			expect(next[1].nested.value).toBe(42)
+		})
+
+		it("can push a draft value directly into its parent array", () => {
+			const base = [{nestedArray: []}]
+			const next = produce(base, s => {
+				s.push(s[0])
+			})
+			expect(next[0].nestedArray).toEqual([])
+			expect(next[1].nestedArray).toEqual([])
+		})
+
+		it("can unshift a spread draft back into the array", () => {
+			const base = [{nestedArray: [1]}]
+			const next = produce(base, s => {
+				s.unshift({...s[0]})
+			})
+			expect(next[0].nestedArray).toEqual([1])
+			expect(next[1].nestedArray).toEqual([1])
+		})
+
+		it("can splice a spread draft into the array", () => {
+			const base = [{nestedArray: ["a", "b"]}]
+			const next = produce(base, s => {
+				s.splice(0, 0, {...s[0]})
+			})
+			expect(next[0].nestedArray).toEqual(["a", "b"])
+			expect(next[1].nestedArray).toEqual(["a", "b"])
+		})
+
 		it("supports assigning undefined to an existing property", () => {
 			const nextState = produce(baseState, s => {
 				s.aProp = undefined

src/plugins/arrayMethods.ts

@@ -4,6 +4,7 @@ import {
 	loadPlugin,
 	markChanged,
 	prepareCopy,
+	handleCrossReference,
 	ProxyArrayState
 } from "../internal"
 
@@ -189,6 +190,30 @@ export function enableArrayMethods() {
 		return Math.min(index, length)
 	}
 
+	/**
+	 * Calls handleCrossReference for each value being inserted into the array,
+	 * and marks the corresponding indices as assigned in `assigned_`.
+	 *
+	 * This ensures nested drafts inside inserted values (e.g. from spreading
+	 * a draft object) are properly finalized, matching the behavior of the
+	 * proxy set trap which calls handleCrossReference on every assignment.
+	 *
+	 * Without this, values containing draft proxies (like `{...state[0]}`)
+	 * pushed via the array methods plugin would have their nested drafts
+	 * revoked during finalization without being replaced by final values.
+	 */
+	function handleInsertedValues(
+		state: ProxyArrayState,
+		startIndex: number,
+		values: any[]
+	) {
+		for (let i = 0; i < values.length; i++) {
+			const index = startIndex + i
+			state.assigned_!.set(index, true)
+			handleCrossReference(state, index, values[i])
+		}
+	}
+
 	/**
 	 * Handles mutating operations that add/remove elements (push, pop, shift, unshift, splice).
 	 *
@@ -204,13 +229,25 @@ export function enableArrayMethods() {
 		args: any[]
 	) {
 		return executeArrayMethod(state, () => {
+			// For push/unshift, capture the length before the operation
+			// so we can compute insertion indices for handleCrossReference
+			const lengthBefore = state.copy_!.length
+
 			const result = (state.copy_! as any)[method](...args)
 
 			// Handle index reassignment for shifting methods
 			if (SHIFTING_METHODS.has(method as MutatingArrayMethod)) {
 				markAllIndicesReassigned(state)
 			}
 
+			// Handle cross-references for newly inserted values.
+			// push appends at the end, unshift inserts at the beginning.
+			if (method === "push" && args.length > 0) {
+				handleInsertedValues(state, lengthBefore, args)
+			} else if (method === "unshift" && args.length > 0) {
+				handleInsertedValues(state, 0, args)
+			}
+
 			// Return appropriate value based on method
 			return RESULT_RETURNING_METHODS.has(method as MutatingArrayMethod)
 				? result
@@ -285,6 +322,14 @@ export function enableArrayMethods() {
 							state.copy_!.splice(...(args as [number, number, ...any[]]))
 						)
 						markAllIndicesReassigned(state)
+						// Handle cross-references for inserted values (args from index 2+)
+						if (args.length > 2) {
+							const startIndex = normalizeSliceIndex(
+								args[0] ?? 0,
+								state.copy_!.length
+							)
+							handleInsertedValues(state, startIndex, args.slice(2))
+						}
 						return res
 					}
 				} else {