diff --git a/apps/mobile/src/lib/threadActivity.test.ts b/apps/mobile/src/lib/threadActivity.test.ts
index 46a79b70acd2..fb85ce1e1cc3 100644
--- a/apps/mobile/src/lib/threadActivity.test.ts
+++ b/apps/mobile/src/lib/threadActivity.test.ts
@@ -1,5 +1,5 @@
 import { derivePendingRequests } from "@t3tools/client-runtime/pending-requests";
-import { describe, expect, it } from "vite-plus/test";
+import { beforeEach, describe, expect, it } from "vite-plus/test";
 
 import {
   ApprovalRequestId,
@@ -27,6 +27,21 @@ import {
   type WorkLogEntry,
 } from "./threadActivity";
 
+// Match Hermes: these ES2023 array methods are absent on mobile.
+beforeEach(() => {
+  const methods = ["toSorted", "toReversed"] 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);
+    }
+  };
+});
+
 const singleSelectQuestion = {
   id: "runtime",
   header: "Runtime",
diff --git a/packages/client-runtime/src/work-log/presentation.ts b/packages/client-runtime/src/work-log/presentation.ts
index 8d62bb0794ca..bfb04eda3247 100644
--- a/packages/client-runtime/src/work-log/presentation.ts
+++ b/packages/client-runtime/src/work-log/presentation.ts
@@ -658,7 +658,9 @@ export function omitSupersededLifecycleMarkers<T>(
     }
   }
 
-  return reversedEntries.toReversed();
+  // Hermes lacks toReversed; this array is local, so reversing it cannot mutate the input.
+  // oxlint-disable-next-line unicorn/no-array-reverse
+  return reversedEntries.reverse();
 }
 
 export function toolGroupSummaryKind(
diff --git a/packages/client-runtime/src/work-log/userInput.ts b/packages/client-runtime/src/work-log/userInput.ts
index 355083c04836..18dea7dd83c2 100644
--- a/packages/client-runtime/src/work-log/userInput.ts
+++ b/packages/client-runtime/src/work-log/userInput.ts
@@ -27,8 +27,9 @@ function questionFingerprint(
   questions: ReadonlyArray<unknown>,
 ): string | undefined {
   const texts = questions.map((question) => (typeof question === "string" ? question.trim() : ""));
+  // Sort the fresh array in place because Hermes does not provide toSorted.
   return texts.length > 0 && texts.every(Boolean)
-    ? JSON.stringify([turnId, texts.toSorted()])
+    ? JSON.stringify([turnId, texts.sort()])
     : undefined;
 }