From ec8eea7cbece64dc301ce93bc201016cc9ca08d0 Mon Sep 17 00:00:00 2001
From: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>
Date: Wed, 8 Jul 2026 17:26:11 -0500
Subject: [PATCH] test(codemode): add Test262 array coverage (#35965)

---
 .../test/array-callbacks-test262.test.ts      | 325 ++++++++++++++++++
 .../codemode/test/array-core-test262.test.ts  | 323 +++++++++++++++++
 packages/codemode/test/parity.test.ts         |  96 +-----
 packages/codemode/test/stdlib.test.ts         |  21 +-
 packages/codemode/test/test262-array.md       |  77 +++++
 5 files changed, 736 insertions(+), 106 deletions(-)
 create mode 100644 packages/codemode/test/array-callbacks-test262.test.ts
 create mode 100644 packages/codemode/test/array-core-test262.test.ts
 create mode 100644 packages/codemode/test/test262-array.md

diff --git a/packages/codemode/test/array-callbacks-test262.test.ts b/packages/codemode/test/array-callbacks-test262.test.ts
new file mode 100644
index 00000000000..3de3a94a4cb
--- /dev/null
+++ b/packages/codemode/test/array-callbacks-test262.test.ts
@@ -0,0 +1,325 @@
+/*
+ * Portions adapted from Test262 at revision 250f204f23a9249ff204be2baec29600faae7b75:
+ * - test/built-ins/Array/prototype/map/15.4.4.19-8-1.js
+ * - test/built-ins/Array/prototype/map/15.4.4.19-8-2.js
+ * - test/built-ins/Array/prototype/map/15.4.4.19-8-b-1.js
+ * - test/built-ins/Array/prototype/filter/15.4.4.20-9-1.js
+ * - test/built-ins/Array/prototype/filter/15.4.4.20-9-2.js
+ * - test/built-ins/Array/prototype/filter/15.4.4.20-9-b-1.js
+ * - test/built-ins/Array/prototype/find/predicate-call-parameters.js
+ * - test/built-ins/Array/prototype/find/predicate-not-called-on-empty-array.js
+ * - test/built-ins/Array/prototype/find/return-found-value-predicate-result-is-true.js
+ * - test/built-ins/Array/prototype/find/return-undefined-if-predicate-returns-false-value.js
+ * - test/built-ins/Array/prototype/findIndex/predicate-call-parameters.js
+ * - test/built-ins/Array/prototype/findIndex/return-index-predicate-result-is-true.js
+ * - test/built-ins/Array/prototype/findIndex/return-negative-one-if-predicate-returns-false-value.js
+ * - test/built-ins/Array/prototype/findLast/predicate-call-parameters.js
+ * - test/built-ins/Array/prototype/findLast/return-found-value-predicate-result-is-true.js
+ * - test/built-ins/Array/prototype/findLast/return-undefined-if-predicate-returns-false-value.js
+ * - test/built-ins/Array/prototype/findLastIndex/predicate-call-parameters.js
+ * - test/built-ins/Array/prototype/findLastIndex/return-index-predicate-result-is-true.js
+ * - test/built-ins/Array/prototype/findLastIndex/return-negative-one-if-predicate-returns-false-value.js
+ * - test/built-ins/Array/prototype/some/15.4.4.17-7-1.js
+ * - test/built-ins/Array/prototype/some/15.4.4.17-8-1.js
+ * - test/built-ins/Array/prototype/every/15.4.4.16-7-1.js
+ * - test/built-ins/Array/prototype/every/15.4.4.16-8-1.js
+ * - test/built-ins/Array/prototype/forEach/15.4.4.18-7-1.js
+ * - test/built-ins/Array/prototype/forEach/15.4.4.18-7-2.js
+ * - test/built-ins/Array/prototype/reduce/15.4.4.21-9-5.js
+ * - test/built-ins/Array/prototype/reduce/15.4.4.21-9-1.js
+ * - test/built-ins/Array/prototype/reduce/15.4.4.21-10-1.js
+ * - test/built-ins/Array/prototype/reduceRight/15.4.4.22-9-5.js
+ * - test/built-ins/Array/prototype/reduceRight/15.4.4.22-9-1.js
+ * - test/built-ins/Array/prototype/reduceRight/15.4.4.22-10-1.js
+ * - test/built-ins/Array/prototype/flatMap/depth-always-one.js
+ * - test/built-ins/Array/prototype/flatMap/mapperfunction-throws.js
+ * - test/built-ins/Array/prototype/sort/S15.4.4.11_A1.1_T1.js
+ * - test/built-ins/Array/prototype/sort/S15.4.4.11_A2.1_T1.js
+ * - test/built-ins/Array/prototype/sort/stability-5-elements.js
+ * - test/built-ins/Array/prototype/toSorted/comparefn-controls-sort.js
+ * - test/built-ins/Array/prototype/toSorted/comparefn-default.js
+ * - test/built-ins/Array/prototype/toSorted/immutable.js
+ * - test/built-ins/Array/prototype/toSorted/zero-or-one-element.js
+ *
+ * Copyright (C) 2015 the V8 project authors. All rights reserved.
+ * Copyright (C) 2018 Mathias Bynens. All rights reserved.
+ * Copyright (C) 2018 Shilpi Jain and Michael Ficarra. All rights reserved.
+ * Copyright (C) 2021 Igalia, S.L. All rights reserved.
+ * Copyright (C) 2021 Microsoft. All rights reserved.
+ * Copyright (C) 2025 Google. All rights reserved.
+ * Copyright (C) 2026 Garham Lee. All rights reserved.
+ * Copyright (c) 2012 Ecma International.  All rights reserved.
+ * Copyright 2009 the Sputnik authors.  All rights reserved.
+ * Test262 portions are governed by the BSD license in LICENSE.test262.
+ */
+import { describe, expect, test } from "bun:test"
+import { Effect } from "effect"
+import { CodeMode } from "../src/index.js"
+
+const value = async (code: string) => {
+  const result = await Effect.runPromise(CodeMode.execute({ code, tools: {} }))
+  if (!result.ok) throw new Error(`expected success, got ${result.error.kind}: ${result.error.message}`)
+  return result.value
+}
+
+const cases = [
+  {
+    path: "test/built-ins/Array/prototype/map/15.4.4.19-8-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = 5; const result = input.map((value) => { input[2] = 3; input[5] = 6; return 1 }); return [result.length, result[5] === undefined]`,
+    expected: [5, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/map/15.4.4.19-8-2.js",
+    code: `const input = [1, 2, 3, 4, 5]; const result = input.map((value) => { input[4] = -1; return value > 0 ? 1 : 0 }); return [result.length, result[4]]`,
+    expected: [5, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/map/15.4.4.19-8-b-1.js",
+    code: `const input = []; input[10] = 0; input.pop(); input[1] = undefined; let calls = 0; const result = input.map(() => { calls += 1; return 1 }); return [result.length, calls, 0 in result, 1 in result]`,
+    expected: [10, 1, false, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/filter/15.4.4.20-9-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = 5; const result = input.filter(() => { input[2] = 3; input[5] = 6; return true }); return result`,
+    expected: [1, 2, 3, 4, 5],
+  },
+  {
+    path: "test/built-ins/Array/prototype/filter/15.4.4.20-9-2.js",
+    code: `const input = [1, 2, 3, 4, 5]; return input.filter((value) => { input[2] = -1; input[4] = -1; return value > 0 })`,
+    expected: [1, 2, 4],
+  },
+  {
+    path: "test/built-ins/Array/prototype/filter/15.4.4.20-9-b-1.js",
+    code: `const input = []; input[9] = 0; input.pop(); input[1] = undefined; let calls = 0; const result = input.filter(() => { calls += 1; return false }); return [result, calls]`,
+    expected: [[], 1],
+  },
+  {
+    path: "test/built-ins/Array/prototype/find/predicate-call-parameters.js",
+    code: `const input = [10, 20]; const seen = []; input.find((value, index, receiver) => { seen.push([value, index, receiver === input]); return false }); return seen`,
+    expected: [
+      [10, 0, true],
+      [20, 1, true],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/find/return-found-value-predicate-result-is-true.js",
+    code: `return [1, 2, 3].find((value) => value > 1)`,
+    expected: 2,
+  },
+  {
+    path: "test/built-ins/Array/prototype/find/return-undefined-if-predicate-returns-false-value.js",
+    code: `return [1, 2, 3].find((value) => value > 4) === undefined`,
+    expected: true,
+  },
+  {
+    path: "test/built-ins/Array/prototype/find/predicate-not-called-on-empty-array.js",
+    code: `let calls = 0; const result = [].find(() => { calls += 1; return true }); return [result === undefined, calls]`,
+    expected: [true, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/findIndex/predicate-call-parameters.js",
+    code: `const input = [10, 20]; const seen = []; input.findIndex((value, index, receiver) => { seen.push([value, index, receiver === input]); return false }); return seen`,
+    expected: [
+      [10, 0, true],
+      [20, 1, true],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/findIndex/return-index-predicate-result-is-true.js",
+    code: `return [1, 2, 3].findIndex((value) => value > 1)`,
+    expected: 1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/findIndex/return-negative-one-if-predicate-returns-false-value.js",
+    code: `return [1, 2, 3].findIndex((value) => value > 4)`,
+    expected: -1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLast/predicate-call-parameters.js",
+    code: `const input = [10, 20]; const seen = []; input.findLast((value, index, receiver) => { seen.push([value, index, receiver === input]); return false }); return seen`,
+    expected: [
+      [20, 1, true],
+      [10, 0, true],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLast/return-found-value-predicate-result-is-true.js",
+    code: `return [1, 2, 3].findLast((value) => value < 3)`,
+    expected: 2,
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLast/return-undefined-if-predicate-returns-false-value.js",
+    code: `return [1, 2, 3].findLast((value) => value > 4) === undefined`,
+    expected: true,
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLastIndex/predicate-call-parameters.js",
+    code: `const input = [10, 20]; const seen = []; input.findLastIndex((value, index, receiver) => { seen.push([value, index, receiver === input]); return false }); return seen`,
+    expected: [
+      [20, 1, true],
+      [10, 0, true],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLastIndex/return-index-predicate-result-is-true.js",
+    code: `return [1, 2, 3].findLastIndex((value) => value < 3)`,
+    expected: 1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/findLastIndex/return-negative-one-if-predicate-returns-false-value.js",
+    code: `return [1, 2, 3].findLastIndex((value) => value > 4)`,
+    expected: -1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/some/15.4.4.17-7-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = 5; const seen = []; const result = input.some((value) => { input[2] = 3; seen.push(value); return false }); return [result, seen.includes(3)]`,
+    expected: [false, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/some/15.4.4.17-8-1.js",
+    code: `return [].some(() => true)`,
+    expected: false,
+  },
+  {
+    path: "test/built-ins/Array/prototype/every/15.4.4.16-7-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = 5; const seen = []; const result = input.every((value) => { input[2] = 3; seen.push(value); return true }); return [result, seen.includes(3)]`,
+    expected: [true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/every/15.4.4.16-8-1.js",
+    code: `return [].every(() => false)`,
+    expected: true,
+  },
+  {
+    path: "test/built-ins/Array/prototype/forEach/15.4.4.18-7-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = 5; let calls = 0; input.forEach(() => { calls += 1; input[2] = 3; input[5] = 6 }); return calls`,
+    expected: 5,
+  },
+  {
+    path: "test/built-ins/Array/prototype/forEach/15.4.4.18-7-2.js",
+    code: `const input = [1, 2, 3]; const seen = []; input.forEach((value, index) => { seen.push(value); if (index === 0) input.pop() }); return seen`,
+    expected: [1, 2],
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduce/15.4.4.21-9-1.js",
+    code: `const input = [1, 2]; input[3] = 4; input[4] = "5"; return input.reduce((accumulator, value) => { input[2] = 3; input[5] = 6; return accumulator + value })`,
+    expected: "105",
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduce/15.4.4.21-9-5.js",
+    code: `let calls = 0; const result = [1].reduce(() => { calls += 1; return 2 }); return [result, calls]`,
+    expected: [1, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduce/15.4.4.21-10-1.js",
+    code: `const input = [1, 2, 3, 4, 5]; input.reduce(() => 1); return input`,
+    expected: [1, 2, 3, 4, 5],
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduceRight/15.4.4.22-9-1.js",
+    code: `const input = ["1", 2]; input[3] = 4; input[4] = "5"; return input.reduceRight((accumulator, value) => { input[2] = 3; input[5] = 6; return accumulator + value })`,
+    expected: "54321",
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduceRight/15.4.4.22-9-5.js",
+    code: `let calls = 0; const result = [1].reduceRight(() => { calls += 1; return 2 }); return [result, calls]`,
+    expected: [1, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/reduceRight/15.4.4.22-10-1.js",
+    code: `const input = [1, 2, 3, 4, 5]; input.reduceRight(() => 1); return input`,
+    expected: [1, 2, 3, 4, 5],
+  },
+  {
+    path: "test/built-ins/Array/prototype/flatMap/depth-always-one.js",
+    code: `return [1, 2, 3].flatMap((value) => [[value * 2]])`,
+    expected: [[2], [4], [6]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/flatMap/mapperfunction-throws.js",
+    code: `try { [1, 2].flatMap(() => { throw "stop" }) } catch (error) { return error === "stop" } return false`,
+    expected: true,
+  },
+  {
+    path: "test/built-ins/Array/prototype/sort/S15.4.4.11_A1.1_T1.js",
+    code: `const input = []; input[2] = 0; input.pop(); input.sort(); return [input.length, input[0] === undefined, input[1] === undefined]`,
+    expected: [2, true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/sort/S15.4.4.11_A2.1_T1.js",
+    code: `return ["z", "y", "x", "w", "v", "u", "t", "s", "r", "q", "p", "o", "n", "M", "L", "K", "J", "I", "H", "G", "F", "E", "D", "C", "B", "A"].sort()`,
+    expected: [
+      "A",
+      "B",
+      "C",
+      "D",
+      "E",
+      "F",
+      "G",
+      "H",
+      "I",
+      "J",
+      "K",
+      "L",
+      "M",
+      "n",
+      "o",
+      "p",
+      "q",
+      "r",
+      "s",
+      "t",
+      "u",
+      "v",
+      "w",
+      "x",
+      "y",
+      "z",
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/sort/stability-5-elements.js",
+    code: `const input = [{ n: "A", r: 2 }, { n: "B", r: 3 }, { n: "C", r: 2 }, { n: "D", r: 3 }, { n: "E", r: 3 }]; return input.sort((left, right) => right.r - left.r).map((item) => item.n).join("")`,
+    expected: "BDEAC",
+  },
+  {
+    path: "test/built-ins/Array/prototype/toSorted/comparefn-controls-sort.js",
+    code: `const mixed = [333, 33, 3, 222, 22, 2, 111, 11, 1]; return [[1, 2, 3, 4].toSorted((a, b) => a - b), [4, 3, 2, 1].toSorted((a, b) => a - b), mixed.toSorted((a, b) => a - b), [1, 2, 3, 4].toSorted((a, b) => b - a), [4, 3, 2, 1].toSorted((a, b) => b - a), mixed.toSorted((a, b) => b - a)]`,
+    expected: [
+      [1, 2, 3, 4],
+      [1, 2, 3, 4],
+      [1, 2, 3, 11, 22, 33, 111, 222, 333],
+      [4, 3, 2, 1],
+      [4, 3, 2, 1],
+      [333, 222, 111, 33, 22, 11, 3, 2, 1],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/toSorted/comparefn-default.js",
+    code: `return [[1, 2, 3, 4].toSorted(), [4, 3, 2, 1].toSorted(), ["a", 2, 1, "z"].toSorted(), [333, 33, 3, 222, 22, 2, 111, 11, 1].toSorted()]`,
+    expected: [
+      [1, 2, 3, 4],
+      [1, 2, 3, 4],
+      [1, 2, "a", "z"],
+      [1, 11, 111, 2, 22, 222, 3, 33, 333],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/toSorted/immutable.js",
+    code: `const input = [2, 0, 1]; const result = input.toSorted(); return [input, result !== input]`,
+    expected: [[2, 0, 1], true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/toSorted/zero-or-one-element.js",
+    code: `const zero = []; const one = [1]; const zeroResult = zero.toSorted(); const oneResult = one.toSorted(); return [zeroResult, oneResult, zeroResult !== zero, oneResult !== one]`,
+    expected: [[], [1], true, true],
+  },
+] as const
+
+describe("Test262 Array callback adaptations", () => {
+  for (const item of cases) {
+    test(item.path, async () => {
+      expect(await value(item.code)).toEqual(item.expected)
+    })
+  }
+})
diff --git a/packages/codemode/test/array-core-test262.test.ts b/packages/codemode/test/array-core-test262.test.ts
new file mode 100644
index 00000000000..a04e1c2566c
--- /dev/null
+++ b/packages/codemode/test/array-core-test262.test.ts
@@ -0,0 +1,323 @@
+/*
+ * Portions adapted from Test262 at revision 250f204f23a9249ff204be2baec29600faae7b75:
+ * - test/built-ins/Array/prototype/includes/samevaluezero.js
+ * - test/built-ins/Array/prototype/includes/using-fromindex.js
+ * - test/built-ins/Array/prototype/join/S15.4.4.5_A3.1_T1.js
+ * - test/built-ins/Array/prototype/join/S15.4.4.5_A3.2_T1.js
+ * - test/built-ins/Array/prototype/slice/S15.4.4.10_A1.2_T2.js
+ * - test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js
+ * - test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js
+ * - test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js
+ * - test/built-ins/Array/prototype/indexOf/fromindex-zero-conversion.js
+ * - test/built-ins/Array/prototype/indexOf/length-zero-returns-minus-one.js
+ * - test/built-ins/Array/prototype/lastIndexOf/fromindex-zero-conversion.js
+ * - test/built-ins/Array/prototype/lastIndexOf/length-zero-returns-minus-one.js
+ * - test/built-ins/Array/prototype/at/returns-item.js
+ * - test/built-ins/Array/prototype/at/returns-item-relative-index.js
+ * - test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js
+ * - test/built-ins/Array/prototype/flat/null-undefined-elements.js
+ * - test/built-ins/Array/prototype/flat/positive-infinity.js
+ * - test/built-ins/Array/prototype/reverse/S15.4.4.8_A1_T1.js
+ * - test/built-ins/Array/prototype/toReversed/immutable.js
+ * - test/built-ins/Array/prototype/toReversed/zero-or-one-element.js
+ * - test/built-ins/Array/prototype/with/immutable.js
+ * - test/built-ins/Array/prototype/with/index-negative.js
+ * - test/built-ins/Array/prototype/push/S15.4.4.7_A1_T1.js
+ * - test/built-ins/Array/prototype/pop/S15.4.4.6_A1.1_T1.js
+ * - test/built-ins/Array/prototype/shift/S15.4.4.9_A1.1_T1.js
+ * - test/built-ins/Array/prototype/unshift/S15.4.4.13_A1_T1.js
+ * - test/built-ins/Array/prototype/splice/S15.4.4.12_A1.1_T1.js
+ * - test/built-ins/Array/prototype/splice/S15.4.4.12_A1.2_T1.js
+ * - test/built-ins/Array/prototype/splice/called_with_one_argument.js
+ * - test/built-ins/Array/prototype/fill/fill-values.js
+ * - test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js
+ * - test/built-ins/Array/prototype/fill/return-this.js
+ * - test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js
+ * - test/built-ins/Array/prototype/copyWithin/return-this.js
+ * - test/built-ins/Array/prototype/keys/iteration.js
+ * - test/built-ins/Array/prototype/values/iteration.js
+ * - test/built-ins/Array/prototype/entries/iteration.js
+ * - test/built-ins/Array/isArray/15.4.3.2-0-3.js
+ * - test/built-ins/Array/isArray/15.4.3.2-0-4.js
+ * - test/built-ins/Array/from/from-array.js
+ * - test/built-ins/Array/from/from-string.js
+ * - test/built-ins/Array/from/array-like-has-length-but-no-indexes-with-values.js
+ * - test/built-ins/Array/of/creates-a-new-array-from-arguments.js
+ *
+ * Copyright (C) 2015 André Bargull. All rights reserved.
+ * Copyright (C) 2015 the V8 project authors. All rights reserved.
+ * Copyright (C) 2016 the V8 project authors. All rights reserved.
+ * Copyright (C) 2018 Shilpi Jain and Michael Ficarra. All rights reserved.
+ * Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+ * Copyright (C) 2020 Rick Waldron. All rights reserved.
+ * Copyright (C) 2021 Igalia, S.L. All rights reserved.
+ * Copyright (c) 2012 Ecma International.  All rights reserved.
+ * Copyright (c) 2014 Hank Yates. All rights reserved.
+ * Copyright (c) 2015 the V8 project authors. All rights reserved.
+ * Copyright (c) 2021 Rick Waldron.  All rights reserved.
+ * Copyright 2009 the Sputnik authors.  All rights reserved.
+ * Copyright 2015 Microsoft Corporation. All rights reserved.
+ * Copyright 2016 The V8 project authors. All rights reserved.
+ * Test262 portions are governed by the BSD license in LICENSE.test262.
+ */
+import { describe, expect, test } from "bun:test"
+import { Effect } from "effect"
+import { CodeMode } from "../src/index.js"
+
+const value = async (code: string) => {
+  const result = await Effect.runPromise(CodeMode.execute({ code, tools: {} }))
+  if (!result.ok) throw new Error(`expected success, got ${result.error.kind}: ${result.error.message}`)
+  return result.value
+}
+
+const cases = [
+  {
+    path: "test/built-ins/Array/prototype/includes/samevaluezero.js",
+    code: `const input = [42, 0, 1, NaN]; return [input.includes(42), input.includes("42"), input.includes([42]), input.includes(true), input.includes(NaN), input.includes(0), input.includes(-0), input.includes(null), input.includes("")]`,
+    expected: [true, false, false, false, true, true, true, false, false],
+  },
+  {
+    path: "test/built-ins/Array/prototype/includes/using-fromindex.js",
+    code: `const input = ["a", "b", "c"]; return [input.includes("a", 0), input.includes("a", 1), input.includes("a", -4), input.includes("a", -3), input.includes("a", -2), input.includes("b", 0), input.includes("b", 1), input.includes("b", 2), input.includes("b", -3), input.includes("b", -2), input.includes("b", -1), input.includes("c", 0), input.includes("c", 2), input.includes("c", 3), input.includes("c", -3), input.includes("c", -1)]`,
+    expected: [true, false, true, true, false, true, true, false, true, true, false, true, true, false, true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/join/S15.4.4.5_A3.1_T1.js",
+    code: `return [[0, 1, 2, 3].join("&"), [0, 1, 2, 3].join("")]`,
+    expected: ["0&1&2&3", "0123"],
+  },
+  {
+    path: "test/built-ins/Array/prototype/join/S15.4.4.5_A3.2_T1.js",
+    code: `return [
+      ["", "", ""].join(""),
+      ["&", "&", "&"].join("&"),
+      [true, true, true].join(),
+      [null, null, null].join(),
+      [undefined, undefined, undefined].join(),
+      [Infinity, Infinity, Infinity].join(),
+      [NaN, NaN, NaN].join(),
+    ]`,
+    expected: ["", "&&&&&", "true,true,true", ",,", ",,", "Infinity,Infinity,Infinity", "NaN,NaN,NaN"],
+  },
+  {
+    path: "test/built-ins/Array/prototype/slice/S15.4.4.10_A1.2_T2.js",
+    code: `return [0, 1, 2, 3, 4].slice(-1, 5)`,
+    expected: [4],
+  },
+  {
+    path: "test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T1.js",
+    code: `return [].concat([0, 1], [2, 3, 4])`,
+    expected: [0, 1, 2, 3, 4],
+  },
+  {
+    path: "test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T2.js",
+    code: `const object = { value: 1 }; const result = [0].concat(object, [1, 2], -1, true, "NaN"); return [result, result[1] === object]`,
+    expected: [[0, { value: 1 }, 1, 2, -1, true, "NaN"], true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/concat/S15.4.4.4_A1_T3.js",
+    code: `const input = [0, 1]; const result = input.concat(); return [result, result !== input]`,
+    expected: [[0, 1], true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/indexOf/fromindex-zero-conversion.js",
+    code: `const result = [true].indexOf(true, -0); return [result, 1 / result === Infinity]`,
+    expected: [0, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/indexOf/length-zero-returns-minus-one.js",
+    code: `return [].indexOf(1)`,
+    expected: -1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/lastIndexOf/fromindex-zero-conversion.js",
+    code: `const result = [true].lastIndexOf(true, -0); return [result, 1 / result === Infinity]`,
+    expected: [0, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/lastIndexOf/length-zero-returns-minus-one.js",
+    code: `return [].lastIndexOf(1)`,
+    expected: -1,
+  },
+  {
+    path: "test/built-ins/Array/prototype/at/returns-item.js",
+    code: `const input = [1, 2, 3, 4, undefined, 5]; return [input.at(0), input.at(1), input.at(2), input.at(3), input.at(4) === undefined, input.at(5)]`,
+    expected: [1, 2, 3, 4, true, 5],
+  },
+  {
+    path: "test/built-ins/Array/prototype/at/returns-item-relative-index.js",
+    code: `const input = [1, 2, 3, 4, undefined, 5]; return [input.at(0), input.at(-1), input.at(-2) === undefined, input.at(-3), input.at(-4)]`,
+    expected: [1, 5, true, 4, 3],
+  },
+  {
+    path: "test/built-ins/Array/prototype/at/returns-undefined-for-out-of-range-index.js",
+    code: `const input = []; return [input.at(-2) === undefined, input.at(0) === undefined, input.at(1) === undefined]`,
+    expected: [true, true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/flat/null-undefined-elements.js",
+    code: `const result = [1, [null, [undefined]]].flat(2); return [result.length, result[0], result[1] === null, result[2] === undefined]`,
+    expected: [3, 1, true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/flat/positive-infinity.js",
+    code: `return [1, [2, [3, [4]]]].flat(Infinity)`,
+    expected: [1, 2, 3, 4],
+  },
+  {
+    path: "test/built-ins/Array/prototype/reverse/S15.4.4.8_A1_T1.js",
+    code: `const empty = []; const one = [1]; const input = [1, 2]; const emptyResult = empty.reverse(); const oneResult = one.reverse(); const result = input.reverse(); return [emptyResult === empty, oneResult === one, result === input, input]`,
+    expected: [true, true, true, [2, 1]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/toReversed/immutable.js",
+    code: `const input = [0, 1, 2]; const result = input.toReversed(); return [input, result !== input]`,
+    expected: [[0, 1, 2], true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/toReversed/zero-or-one-element.js",
+    code: `const zero = []; const one = [1]; const zeroResult = zero.toReversed(); const oneResult = one.toReversed(); return [zeroResult, oneResult, zeroResult !== zero, oneResult !== one]`,
+    expected: [[], [1], true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/with/immutable.js",
+    code: `const input = [0, 1, 2]; const result = input.with(1, 3); return [input, result !== input, input.with(1, 1) !== input]`,
+    expected: [[0, 1, 2], true, true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/with/index-negative.js",
+    code: `const input = [0, 1, 2]; return [input.with(-1, 4), input.with(-3, 4)]`,
+    expected: [
+      [0, 1, 4],
+      [4, 1, 2],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/push/S15.4.4.7_A1_T1.js",
+    code: `const input = []; return [input.push(1), input.push(), input.push(-1), input]`,
+    expected: [1, 1, 2, [1, -1]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/pop/S15.4.4.6_A1.1_T1.js",
+    code: `const input = []; return [input.pop() === undefined, input.length]`,
+    expected: [true, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/shift/S15.4.4.9_A1.1_T1.js",
+    code: `const input = []; return [input.shift() === undefined, input.length]`,
+    expected: [true, 0],
+  },
+  {
+    path: "test/built-ins/Array/prototype/unshift/S15.4.4.13_A1_T1.js",
+    code: `const input = []; return [input.unshift(1), input[0], input.unshift(), input.unshift(-1), input]`,
+    expected: [1, 1, 1, 2, [-1, 1]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/splice/S15.4.4.12_A1.1_T1.js",
+    code: `const input = [0, 1, 2, 3]; const removed = input.splice(0, 3); return [input, removed]`,
+    expected: [[3], [0, 1, 2]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/splice/S15.4.4.12_A1.2_T1.js",
+    code: `const input = [0, 1]; const removed = input.splice(-2, -1); return [input, removed]`,
+    expected: [[0, 1], []],
+  },
+  {
+    path: "test/built-ins/Array/prototype/splice/called_with_one_argument.js",
+    code: `const input = ["first", "second", "third"]; const removed = input.splice(1); return [input, removed]`,
+    expected: [["first"], ["second", "third"]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/fill/fill-values-custom-start-and-end.js",
+    code: `const input = [0, 0, 0, 0, 0]; input.fill(8, -3, 4); const sparse = []; sparse[4] = 0; sparse.fill(8, 1, 3); return [[0, 0, 0].fill(8, 1, 2), input, [0, 0, 0, 0, 0].fill(8, -2, -1), [0, 0, 0, 0, 0].fill(8, -1, -3), [0 in sparse, sparse[1], sparse[2], 3 in sparse, sparse[4]]]`,
+    expected: [
+      [0, 8, 0],
+      [0, 0, 8, 8, 0],
+      [0, 0, 0, 8, 0],
+      [0, 0, 0, 0, 0],
+      [false, 8, 8, false, 0],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/fill/return-this.js",
+    code: `const input = []; return input.fill(1) === input`,
+    expected: true,
+  },
+  {
+    path: "test/built-ins/Array/prototype/fill/fill-values.js",
+    code: `const omitted = [0, 0].fill(); return [[].fill(8), omitted.map((value) => value === undefined), [0, 0, 0].fill(8)]`,
+    expected: [[], [true, true], [8, 8, 8]],
+  },
+  {
+    path: "test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js",
+    code: `return [[0, 1, 2, 3].copyWithin(0, 0, 0), [0, 1, 2, 3].copyWithin(0, 0, 2), [0, 1, 2, 3].copyWithin(0, 1, 2), [0, 1, 2, 3].copyWithin(1, 0, 2), [0, 1, 2, 3, 4, 5].copyWithin(1, 3, 5)]`,
+    expected: [
+      [0, 1, 2, 3],
+      [0, 1, 2, 3],
+      [1, 1, 2, 3],
+      [0, 0, 1, 3],
+      [0, 3, 4, 3, 4, 5],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/prototype/copyWithin/return-this.js",
+    code: `const input = [0, 1, 2, 3]; const result = input.copyWithin(1, 0, 2); return [input, result === input]`,
+    expected: [[0, 0, 1, 3], true],
+  },
+  {
+    path: "test/built-ins/Array/prototype/keys/iteration.js",
+    code: `return ["a", "b", "c"].keys()`,
+    expected: [0, 1, 2],
+  },
+  {
+    path: "test/built-ins/Array/prototype/values/iteration.js",
+    code: `return ["a", "b", "c"].values()`,
+    expected: ["a", "b", "c"],
+  },
+  {
+    path: "test/built-ins/Array/prototype/entries/iteration.js",
+    code: `return ["a", "b"].entries()`,
+    expected: [
+      [0, "a"],
+      [1, "b"],
+    ],
+  },
+  {
+    path: "test/built-ins/Array/isArray/15.4.3.2-0-3.js",
+    code: `return [Array.isArray([]), Array.isArray([1]), Array.isArray(Array.of(1))]`,
+    expected: [true, true, true],
+  },
+  {
+    path: "test/built-ins/Array/isArray/15.4.3.2-0-4.js",
+    code: `return [Array.isArray(42), Array.isArray({}), Array.isArray(null), Array.isArray("array")]`,
+    expected: [false, false, false, false],
+  },
+  {
+    path: "test/built-ins/Array/from/from-array.js",
+    code: `const input = [0, "foo", undefined, Infinity]; const result = Array.from(input); return [result.length, result[0], result[1], result[2] === undefined, result[3] === Infinity, result !== input, result instanceof Array]`,
+    expected: [4, 0, "foo", true, true, true, true],
+  },
+  {
+    path: "test/built-ins/Array/from/from-string.js",
+    code: `return Array.from("Test")`,
+    expected: ["T", "e", "s", "t"],
+  },
+  {
+    path: "test/built-ins/Array/from/array-like-has-length-but-no-indexes-with-values.js",
+    code: `const result = Array.from({ length: 5 }); const mapped = result.map(() => 1); return [result.length, result.map((value) => value === undefined), mapped.length, mapped]`,
+    expected: [5, [true, true, true, true, true], 5, [1, 1, 1, 1, 1]],
+  },
+  {
+    path: "test/built-ins/Array/of/creates-a-new-array-from-arguments.js",
+    code: `const mixed = Array.of(undefined, false, null, undefined); return [Array.of("Mike", "Rick", "Leo"), mixed.length, mixed[0] === undefined, mixed[1], mixed[2], mixed[3] === undefined, Array.of()]`,
+    expected: [["Mike", "Rick", "Leo"], 4, true, false, null, true, []],
+  },
+] as const
+
+describe("Test262 Array core adaptations", () => {
+  for (const item of cases) {
+    test(item.path, async () => {
+      expect(await value(item.code)).toEqual(item.expected)
+    })
+  }
+})
diff --git a/packages/codemode/test/parity.test.ts b/packages/codemode/test/parity.test.ts
index 5593831127a..c8046a69671 100644
--- a/packages/codemode/test/parity.test.ts
+++ b/packages/codemode/test/parity.test.ts
@@ -42,11 +42,6 @@ describe("H2: string property access reads as undefined (not a throw)", () => {
   test("unknown property on a number is undefined", async () => {
     expect(await value(`return (5).foo ?? "n"`)).toBe("n")
   })
-
-  test("supported string methods still work", async () => {
-    expect(await value(`return "AB".toLowerCase()`)).toBe("ab")
-    expect(await value(`return "hello".length`)).toBe(5)
-  })
 })
 
 describe("H3: array property access reads as undefined (not a throw)", () => {
@@ -63,8 +58,7 @@ describe("H3: array property access reads as undefined (not a throw)", () => {
     expect(await value(`return [1,2,3].toSpliced === undefined`)).toBe(true)
   })
 
-  test("supported array methods and indexing still work", async () => {
-    expect(await value(`return [1,2,3].map(x => x + 1)`)).toEqual([2, 3, 4])
+  test("array indexing still works", async () => {
     expect(await value(`return [1,2,3][9] === undefined`)).toBe(true)
     expect(await value(`return [1,2,3][9]`)).toBeNull()
   })
@@ -202,9 +196,6 @@ describe("Error values and instanceof", () => {
       "TypeError",
       true,
     ])
-    expect(await value(`try { "a".normalize("NOPE") } catch (e) { return [e.name, e instanceof RangeError] }`)).toEqual(
-      ["RangeError", true],
-    )
     expect(await value(`try { "a".match("(") } catch (e) { return [e.name, e instanceof SyntaxError] }`)).toEqual([
       "SyntaxError",
       true,
@@ -263,55 +254,18 @@ describe("Error values and instanceof", () => {
   })
 })
 
-describe("array methods: splice, fill, copyWithin, keys/values/entries", () => {
-  test("sort and reverse mutate and return the receiver", async () => {
+describe("CodeMode-specific array behavior", () => {
+  test("sort with a comparator mutates and returns the receiver", async () => {
     expect(
       await value(`
-        const sorted = [3, 1, 2]
-        const sortResult = sorted.sort((a, b) => a - b)
-        const reversed = [1, 2, 3]
-        const reverseResult = reversed.reverse()
-        return { sorted, sameSort: sorted === sortResult, reversed, sameReverse: reversed === reverseResult }
+        const input = [3, 1, 2]
+        const result = input.sort((a, b) => a - b)
+        return { input, same: input === result }
       `),
-    ).toEqual({ sorted: [1, 2, 3], sameSort: true, reversed: [3, 2, 1], sameReverse: true })
+    ).toEqual({ input: [1, 2, 3], same: true })
   })
 
-  test("array callbacks receive the receiver and observe later mutations", async () => {
-    expect(
-      await value(`
-        const values = [1, 2, 3]
-        const seen = values.map((value, index, receiver) => {
-          if (index === 0) values[1] = 9
-          return [value, receiver === values]
-        })
-        return seen
-      `),
-    ).toEqual([
-      [1, true],
-      [9, true],
-      [3, true],
-    ])
-    expect(
-      await value(`
-        const values = [1, 2, 3]
-        const seen = []
-        values.forEach((value, index) => {
-          seen.push(value)
-          if (index === 0) values.pop()
-        })
-        return seen
-      `),
-    ).toEqual([1, 2])
-  })
-
-  test("splice removes in place and returns the removed elements", async () => {
-    expect(await value(`const a = [1,2,3,4]; const removed = a.splice(1, 2); return { removed, a }`)).toEqual({
-      removed: [2, 3],
-      a: [1, 4],
-    })
-  })
-
-  test("splice inserts new elements at the cut", async () => {
+  test("splice can replace and insert elements", async () => {
     expect(await value(`const a = ["a","d"]; a.splice(1, 0, "b", "c"); return a`)).toEqual(["a", "b", "c", "d"])
     expect(await value(`const a = [1,2,3]; const removed = a.splice(1, 1, "x"); return { removed, a }`)).toEqual({
       removed: [2],
@@ -319,32 +273,12 @@ describe("array methods: splice, fill, copyWithin, keys/values/entries", () => {
     })
   })
 
-  test("splice with one argument removes to the end; negative start counts back", async () => {
-    expect(await value(`const a = [1,2,3]; const removed = a.splice(1); return { removed, a }`)).toEqual({
-      removed: [2, 3],
-      a: [1],
-    })
-    expect(await value(`const a = [1,2,3]; const removed = a.splice(-1); return { removed, a }`)).toEqual({
-      removed: [3],
-      a: [1, 2],
-    })
-  })
-
   test("splice rejects inserting a container into itself", async () => {
     const err = await error(`const a = [1]; a.splice(0, 0, [a]); return a`)
     expect(err.kind).toBe("InvalidDataValue")
     expect(err.message).toContain("circular")
   })
 
-  test("fill overwrites a range and returns the mutated array", async () => {
-    expect(await value(`const a = [1,2,3,4]; return a.fill(0, 1, 3)`)).toEqual([1, 0, 0, 4])
-    expect(await value(`return [1,2,3].fill("z")`)).toEqual(["z", "z", "z"])
-  })
-
-  test("copyWithin copies a range in place", async () => {
-    expect(await value(`return [1,2,3,4,5].copyWithin(0, 3)`)).toEqual([4, 5, 3, 4, 5])
-  })
-
   test("keys/values/entries return arrays usable with for...of and spread", async () => {
     expect(await value(`return [...["x","y","z"].keys()]`)).toEqual([0, 1, 2])
     expect(await value(`return ["x","y"].values()`)).toEqual(["x", "y"])
@@ -359,16 +293,9 @@ describe("array methods: splice, fill, copyWithin, keys/values/entries", () => {
   })
 })
 
-describe("string methods: localeCompare, normalize, trim aliases", () => {
+describe("CodeMode-specific string behavior", () => {
   test("localeCompare orders strings for sorting", async () => {
     expect(await value(`return ["b","a","c"].sort((x, y) => x.localeCompare(y))`)).toEqual(["a", "b", "c"])
-    expect(await value(`return "a".localeCompare("a")`)).toBe(0)
-  })
-
-  test("normalize applies unicode normalization forms", async () => {
-    expect(await value(`return "\\u0065\\u0301".normalize("NFC").length`)).toBe(1)
-    expect(await value(`return "\\u00e9".normalize("NFD").length`)).toBe(2)
-    expect(await value(`return "x".normalize() === "x"`)).toBe(true)
   })
 
   test("an invalid normalize form is a clear catchable error", async () => {
@@ -453,11 +380,6 @@ describe("H5: builtin coercion functions work as array callbacks", () => {
     expect(await value(`return [1, 2, 3].map(String)`)).toEqual(["1", "2", "3"])
   })
 
-  test("arrow callbacks still work (no regression)", async () => {
-    expect(await value(`return [1, 2, 3, 4].filter(x => x % 2 === 0)`)).toEqual([2, 4])
-    expect(await value(`return [1, 2, 3].reduce((a, b) => a + b, 0)`)).toBe(6)
-  })
-
   test("a non-callable callback is still rejected", async () => {
     const err = await error(`return [1,2,3].map(42)`)
     expect(err.message).toContain("callback")
diff --git a/packages/codemode/test/stdlib.test.ts b/packages/codemode/test/stdlib.test.ts
index d5870dab8de..dc9710bd2fc 100644
--- a/packages/codemode/test/stdlib.test.ts
+++ b/packages/codemode/test/stdlib.test.ts
@@ -154,9 +154,7 @@ describe("RegExp", () => {
     ).toEqual(["1", "22"])
   })
 
-  test("string match: non-global carries index, global lists all matches", async () => {
-    expect(await value(`const m = "a1b22".match(/\\d+/); return [m[0], m.index]`)).toEqual(["1", 1])
-    expect(await value(`return "a1b22".match(/\\d+/g)`)).toEqual(["1", "22"])
+  test("an unmatched string pattern returns null", async () => {
     expect(await value(`return "abc".match(/\\d/)`)).toBeNull()
   })
 
@@ -164,13 +162,6 @@ describe("RegExp", () => {
     expect(await value(`return "a1b22".matchAll(/(\\d+)/g).map((m) => m[1])`)).toEqual(["1", "22"])
   })
 
-  test("replace and replaceAll with patterns and $1 substitution", async () => {
-    expect(await value(`return "a1b2".replace(/\\d/, "#")`)).toBe("a#b2")
-    expect(await value(`return "a1b2".replace(/\\d/g, "#")`)).toBe("a#b#")
-    expect(await value(`return "a1b2".replaceAll(/\\d/g, "#")`)).toBe("a#b#")
-    expect(await value(`return "hi bob".replace(/b(o)b/, "[$1]")`)).toBe("hi [o]")
-  })
-
   test("function replacers receive captures, offsets, input, and named groups", async () => {
     expect(
       await value(`
@@ -236,12 +227,6 @@ describe("RegExp", () => {
     expect(await value(`try { "a".replaceAll(/a/, "b"); return "no" } catch { return "caught" }`)).toBe("caught")
   })
 
-  test("split and search accept patterns", async () => {
-    expect(await value(`return "a1b22c".split(/\\d+/)`)).toEqual(["a", "b", "c"])
-    expect(await value(`return "ab42".search(/\\d/)`)).toBe(2)
-    expect(await value(`return "ab".search(/\\d/)`)).toBe(-1)
-  })
-
   test("new RegExp constructs from strings; invalid patterns are catchable", async () => {
     expect(await value(`return new RegExp("a+", "i").test("AAA")`)).toBe(true)
     expect(await value(`try { new RegExp("("); return "no" } catch { return "caught" }`)).toBe("caught")
@@ -650,9 +635,7 @@ describe("stdlib integration", () => {
       true,
     )
     expect(
-      await value(
-        `try { Object.fromEntries(new Map([["fn", Math.max]])); return false } catch { return true }`,
-      ),
+      await value(`try { Object.fromEntries(new Map([["fn", Math.max]])); return false } catch { return true }`),
     ).toBe(true)
   })
 
diff --git a/packages/codemode/test/test262-array.md b/packages/codemode/test/test262-array.md
new file mode 100644
index 00000000000..b8e7e07a897
--- /dev/null
+++ b/packages/codemode/test/test262-array.md
@@ -0,0 +1,77 @@
+# Test262 Array Coverage
+
+The Array tests adapt Test262 at revision `250f204f23a9249ff204be2baec29600faae7b75`. They cover CodeMode's 35
+exposed instance methods and three static methods using actual arrays, accepted argument types, deterministic behavior,
+and CodeMode's materialized collection conventions. Each executable case names its exact upstream source path.
+`LICENSE.test262` contains the upstream BSD terms.
+
+This is coverage of CodeMode's bounded Array surface, not a claim of ECMAScript or Test262 conformance. One upstream
+file may contain both adapted and inapplicable assertions, so a cited source means only that the represented assertions
+were adapted.
+
+## Inventory
+
+The 38 relevant upstream API directories contain 2,837 files. The executable suite adapts assertions from 83 distinct
+sources.
+
+| API                             | Upstream files | Adapted sources |
+| ------------------------------- | -------------: | --------------: |
+| `Array.prototype.map`           |            216 |               3 |
+| `Array.prototype.filter`        |            242 |               3 |
+| `Array.prototype.find`          |             23 |               4 |
+| `Array.prototype.findIndex`     |             23 |               3 |
+| `Array.prototype.findLast`      |             24 |               3 |
+| `Array.prototype.findLastIndex` |             24 |               3 |
+| `Array.prototype.some`          |            219 |               2 |
+| `Array.prototype.every`         |            218 |               2 |
+| `Array.prototype.includes`      |             30 |               2 |
+| `Array.prototype.join`          |             23 |               2 |
+| `Array.prototype.reduce`        |            260 |               3 |
+| `Array.prototype.reduceRight`   |            260 |               3 |
+| `Array.prototype.flatMap`       |             24 |               2 |
+| `Array.prototype.forEach`       |            190 |               2 |
+| `Array.prototype.sort`          |             54 |               3 |
+| `Array.prototype.toSorted`      |             21 |               4 |
+| `Array.prototype.slice`         |             71 |               1 |
+| `Array.prototype.concat`        |             69 |               3 |
+| `Array.prototype.indexOf`       |            201 |               2 |
+| `Array.prototype.lastIndexOf`   |            198 |               2 |
+| `Array.prototype.at`            |             13 |               3 |
+| `Array.prototype.flat`          |             19 |               2 |
+| `Array.prototype.reverse`       |             18 |               1 |
+| `Array.prototype.toReversed`    |             17 |               2 |
+| `Array.prototype.with`          |             21 |               2 |
+| `Array.prototype.push`          |             24 |               1 |
+| `Array.prototype.pop`           |             23 |               1 |
+| `Array.prototype.shift`         |             20 |               1 |
+| `Array.prototype.unshift`       |             22 |               1 |
+| `Array.prototype.splice`        |             81 |               3 |
+| `Array.prototype.fill`          |             22 |               3 |
+| `Array.prototype.copyWithin`    |             39 |               2 |
+| `Array.prototype.keys`          |             12 |               1 |
+| `Array.prototype.values`        |             12 |               1 |
+| `Array.prototype.entries`       |             12 |               1 |
+| `Array.from`                    |             47 |               3 |
+| `Array.isArray`                 |             29 |               2 |
+| `Array.of`                      |             16 |               1 |
+
+## Exclusions
+
+Assertions are not adapted when they test behavior outside CodeMode's documented Array surface:
+
+- Function metadata, property descriptors, constructibility, prototype mutation, species constructors, or cross-realm
+  identity.
+- Generic receivers, detached methods, `.call`, `.apply`, boxed values, custom coercion objects, Symbols, BigInts,
+  proxies, accessors, frozen arrays, typed arrays, or ArrayBuffers.
+- `Array.from` mappers, custom iterables, constructor substitution, and iterator-closing behavior.
+- Native iterator identity, `.next()`, completion records, or live iterator mutation. CodeMode deliberately materializes
+  `keys`, `values`, and `entries` as arrays.
+- Sparse-array assertions that depend on literal elisions or inherited indexed properties. CodeMode's confined data
+  model does not preserve those prototype and hole semantics at every boundary.
+- Argument coercions outside the accepted schema-like surface. Numeric positions must be numbers and `join` separators
+  must be strings.
+- Exact native error brands where CodeMode exposes a safe runtime error instead.
+- Async/effectful callbacks, circular-data rejection, sandbox-value identity, diagnostics, and host-boundary behavior.
+  Those remain covered by CodeMode-specific tests.
+
+Handwritten tests remain where they specify CodeMode behavior rather than ordinary ECMAScript Array semantics.