diff --git a/oxlint-plugin-t3code/index.ts b/oxlint-plugin-t3code/index.ts
index 5037dc94341372fbc28b70855171ee05a9cce65d..a2d1997e43f9defe1233de5d69bb0879fe6d089e 100644
--- a/oxlint-plugin-t3code/index.ts
+++ b/oxlint-plugin-t3code/index.ts
@@ -2,6 +2,7 @@ import { definePlugin } from "@oxlint/plugins";
 
 import namespaceNodeImports from "./rules/namespace-node-imports.ts";
 import noGlobalProcessRuntime from "./rules/no-global-process-runtime.ts";
+import noHermesUnsupportedArrayMethods from "./rules/no-hermes-unsupported-array-methods.ts";
 import noInlineSchemaCompile from "./rules/no-inline-schema-compile.ts";
 import noManualEffectRuntimeInTests from "./rules/no-manual-effect-runtime-in-tests.ts";
 import noMobileUniwindThemeEscapeHatches from "./rules/no-mobile-uniwind-theme-escape-hatches.ts";
@@ -14,6 +15,7 @@ export default definePlugin({
   rules: {
     "namespace-node-imports": namespaceNodeImports,
     "no-global-process-runtime": noGlobalProcessRuntime,
+    "no-hermes-unsupported-array-methods": noHermesUnsupportedArrayMethods,
     "no-inline-schema-compile": noInlineSchemaCompile,
     "no-manual-effect-runtime-in-tests": noManualEffectRuntimeInTests,
     "no-mobile-uniwind-theme-escape-hatches": noMobileUniwindThemeEscapeHatches,
diff --git a/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.test.ts b/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.test.ts
new file mode 100644
index 0000000000000000000000000000000000000000..4bd751c13c9a3eefe46c49e65cfadb6e136c8594
--- /dev/null
+++ b/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.test.ts
@@ -0,0 +1,57 @@
+import { assert, describe } from "@effect/vitest";
+
+import { createOxlintRuleHarness } from "../test/utils.ts";
+
+const rule = createOxlintRuleHarness("t3code/no-hermes-unsupported-array-methods", {
+  filename: "fixture.ts",
+});
+
+describe("t3code/no-hermes-unsupported-array-methods", () => {
+  rule.valid("allows in-place sort on a copy", `const sorted = [...items].sort(compare);`);
+
+  rule.valid("allows in-place reverse on a copy", `const reversed = [...items].reverse();`);
+
+  rule.valid(
+    "allows other ES2023 methods Hermes ships",
+    `const last = items.findLast(Boolean); const tail = items.at(-1);`,
+  );
+
+  rule.valid(
+    "ignores property reads that are not calls",
+    `const hasToSorted = typeof Array.prototype.toSorted === "function";`,
+  );
+
+  rule.invalid("reports toSorted", `const sorted = items.toSorted(compare);`, (output) => {
+    assert.match(output, /Array#toSorted/);
+  });
+
+  rule.invalid(
+    "reports toReversed in a chain",
+    `const open = chains.map((chain) => chain.layers.toReversed().filter(isOpen));`,
+    (output) => {
+      assert.match(output, /Array#toReversed/);
+    },
+  );
+
+  rule.invalid(
+    "reports toSpliced via computed access with a copy-then-splice remediation",
+    `const next = items["toSpliced"](0, 1);`,
+    (output) => {
+      assert.match(output, /Array#toSpliced/);
+      assert.match(output, /const copy = \[\.\.\.array\]; copy\.splice\(\.\.\.\); use copy/);
+    },
+  );
+
+  rule.invalid(
+    "reports a static template-literal property name",
+    "const reversed = items[`toReversed`]();",
+    (output) => {
+      assert.match(output, /Array#toReversed/);
+    },
+  );
+
+  rule.valid(
+    "ignores a template-literal property with substitutions",
+    "const value = items[`to${suffix}`]();",
+  );
+});
diff --git a/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.ts b/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.ts
new file mode 100644
index 0000000000000000000000000000000000000000..e5dd8867e69647e9a9608059ae74a5a662fe356b
--- /dev/null
+++ b/oxlint-plugin-t3code/rules/no-hermes-unsupported-array-methods.ts
@@ -0,0 +1,45 @@
+import { defineRule } from "@oxlint/plugins";
+
+// ES2023 change-array-by-copy methods. Hermes does not implement them, and
+// tsconfig targets ESNext, so nothing but this rule stands between a call and a
+// TypeError that is fatal on every mobile launch that reaches it.
+const UNSUPPORTED_METHODS = new Map([
+  ["toSorted", "[...array].sort(...)"],
+  ["toReversed", "[...array].reverse()"],
+  // splice returns the removed elements, so the copy itself is the result.
+  ["toSpliced", "const copy = [...array]; copy.splice(...); use copy"],
+]);
+
+export default defineRule({
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Disallow ES2023 array-by-copy methods (toSorted, toReversed, toSpliced) in code that runs on Hermes.",
+    },
+  },
+  create(context) {
+    return {
+      CallExpression(node) {
+        if (node.callee.type !== "MemberExpression") return;
+        const { property } = node.callee;
+        const name =
+          property.type === "Identifier"
+            ? property.name
+            : property.type === "Literal" && typeof property.value === "string"
+              ? property.value
+              : property.type === "TemplateLiteral" && property.expressions.length === 0
+                ? (property.quasis[0]?.value.cooked ?? null)
+                : null;
+        if (name === null) return;
+        const replacement = UNSUPPORTED_METHODS.get(name);
+        if (replacement === undefined) return;
+
+        context.report({
+          node: property,
+          message: `Hermes does not implement Array#${name}. Copy the array first: ${replacement}.`,
+        });
+      },
+    };
+  },
+});
diff --git a/packages/shared/src/threadPullRequests.test.ts b/packages/shared/src/threadPullRequests.test.ts
index 05fc7b12b021e9101b1b069fa950fe7dc325a0db..6f231f28989b3b4ea044adb94cd213ed1a2769a4 100644
--- a/packages/shared/src/threadPullRequests.test.ts
+++ b/packages/shared/src/threadPullRequests.test.ts
@@ -3,7 +3,7 @@ import {
   type ThreadPullRequestLink,
   type ThreadPullRequestSnapshot,
 } from "@t3tools/contracts";
-import { describe, expect, it } from "vite-plus/test";
+import { beforeEach, describe, expect, it } from "vite-plus/test";
 
 import {
   legacyLinkedPullRequestOf,
@@ -15,6 +15,22 @@ import {
   threadPullRequestKeysEqual,
 } from "./threadPullRequests.ts";
 
+// Match Hermes: these ES2023 array methods are absent on mobile, and this module runs in
+// the home thread list on every launch.
+beforeEach(() => {
+  const methods = ["toSorted", "toReversed", "toSpliced"] as const;
+  const descriptors = methods.map((method) =>
+    Object.getOwnPropertyDescriptor(Array.prototype, method),
+  );
+  for (const method of methods) Reflect.deleteProperty(Array.prototype, method);
+  return () => {
+    for (const [index, method] of methods.entries()) {
+      const descriptor = descriptors[index];
+      if (descriptor) Reflect.defineProperty(Array.prototype, method, descriptor);
+    }
+  };
+});
+
 function snapshot(input: Partial<ThreadPullRequestSnapshot> = {}): ThreadPullRequestSnapshot {
   return {
     state: "open",
diff --git a/packages/shared/src/threadPullRequests.ts b/packages/shared/src/threadPullRequests.ts
index 5d91d98d52c99b4e8c83e4ef7d6a1fc96ef8bd9a..55e23027832da3dc1e7fa39754e2dfe91fa14140 100644
--- a/packages/shared/src/threadPullRequests.ts
+++ b/packages/shared/src/threadPullRequests.ts
@@ -106,8 +106,10 @@ export function resolveThreadCurrentPullRequest(
   if (open.length === 1) return { kind: "single", link: open[0]! };
   const chains = resolveThreadPullRequestChains(visible);
   if (open.length > 1) {
+    // `.reverse()` on a copy, not `.toReversed()`: this runs on Hermes, which has no ES2023
+    // array methods, and a TypeError here is fatal on every mobile launch that renders a stack.
     const openChains = chains
-      .map((chain) => chain.layers.toReversed().filter(isOpen))
+      .map((chain) => [...chain.layers].reverse().filter(isOpen))
       .filter((layers) => layers.length > 0)
       .sort(
         (left, right) =>
diff --git a/vite.config.ts b/vite.config.ts
index e26d5d6e653e25e49480944a7eb201346b7752d4..b9f2c9cc2c4b335c607dc59bbe5ac60c6393e29e 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -135,6 +135,19 @@ export default defineConfig({
         files: ["apps/mobile/src/**"],
         rules: { "t3code/no-mobile-uniwind-theme-escape-hatches": "error" },
       },
+      {
+        // Code that runs on Hermes. It has no ES2023 change-array-by-copy methods, and
+        // tsconfig targets ESNext, so only lint stands between a call and a fatal launch.
+        // Tests run on Node and are exempt.
+        files: [
+          "apps/mobile/src/**",
+          "packages/client-runtime/src/**",
+          "packages/contracts/src/**",
+          "packages/shared/src/**",
+        ],
+        excludeFiles: ["**/*.test.ts", "**/*.test.tsx"],
+        rules: { "t3code/no-hermes-unsupported-array-methods": "error" },
+      },
       {
         // Reviewed native and third-party interop boundaries that cannot consume a className.
         files: [