diff --git a/ui/src/ui/controllers/chat.ts b/ui/src/ui/controllers/chat.ts
index 0957bd27b..4e097c67c 100644
--- a/ui/src/ui/controllers/chat.ts
+++ b/ui/src/ui/controllers/chat.ts
@@ -1,4 +1,5 @@
 import type { GatewayBrowserClient } from "../gateway";
+import { generateUUID } from "../uuid";
 
 export type ChatState = {
   client: GatewayBrowserClient | null;
@@ -48,7 +49,7 @@ export async function sendChat(state: ChatState) {
   state.chatSending = true;
   state.chatMessage = "";
   state.lastError = null;
-  const runId = crypto.randomUUID();
+  const runId = generateUUID();
   state.chatRunId = runId;
   state.chatStream = "";
   try {
diff --git a/ui/src/ui/gateway.ts b/ui/src/ui/gateway.ts
index 7fd488498..7dd7722b3 100644
--- a/ui/src/ui/gateway.ts
+++ b/ui/src/ui/gateway.ts
@@ -1,3 +1,5 @@
+import { generateUUID } from "./uuid";
+
 export type GatewayEventFrame = {
   type: "event";
   event: string;
@@ -167,7 +169,7 @@ export class GatewayBrowserClient {
     if (!this.ws || this.ws.readyState !== WebSocket.OPEN) {
       return Promise.reject(new Error("gateway not connected"));
     }
-    const id = crypto.randomUUID();
+    const id = generateUUID();
     const frame = { type: "req", id, method, params };
     const p = new Promise<T>((resolve, reject) => {
       this.pending.set(id, { resolve: (v) => resolve(v as T), reject });
diff --git a/ui/src/ui/uuid.test.ts b/ui/src/ui/uuid.test.ts
new file mode 100644
index 000000000..62856f1b6
--- /dev/null
+++ b/ui/src/ui/uuid.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+
+import { generateUUID } from "./uuid";
+
+describe("generateUUID", () => {
+  it("uses crypto.randomUUID when available", () => {
+    const id = generateUUID({
+      randomUUID: () => "randomuuid",
+      getRandomValues: () => {
+        throw new Error("should not be called");
+      },
+    });
+
+    expect(id).toBe("randomuuid");
+  });
+
+  it("falls back to crypto.getRandomValues", () => {
+    const id = generateUUID({
+      getRandomValues: (bytes) => {
+        for (let i = 0; i < bytes.length; i++) bytes[i] = i;
+        return bytes;
+      },
+    });
+
+    expect(id).toBe("00010203-0405-4607-8809-0a0b0c0d0e0f");
+  });
+
+  it("still returns a v4 UUID when crypto is missing", () => {
+    const id = generateUUID(null);
+    expect(id).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/);
+  });
+});
+
diff --git a/ui/src/ui/uuid.ts b/ui/src/ui/uuid.ts
new file mode 100644
index 000000000..7124dbb8f
--- /dev/null
+++ b/ui/src/ui/uuid.ts
@@ -0,0 +1,43 @@
+export type CryptoLike = {
+  randomUUID?: (() => string) | undefined;
+  getRandomValues?: ((array: Uint8Array) => Uint8Array) | undefined;
+};
+
+function uuidFromBytes(bytes: Uint8Array): string {
+  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
+  bytes[8] = (bytes[8] & 0x3f) | 0x80; // variant 1
+
+  let hex = "";
+  for (let i = 0; i < bytes.length; i++) {
+    hex += bytes[i]!.toString(16).padStart(2, "0");
+  }
+
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(
+    16,
+    20,
+  )}-${hex.slice(20)}`;
+}
+
+function weakRandomBytes(): Uint8Array {
+  const bytes = new Uint8Array(16);
+  const now = Date.now();
+  for (let i = 0; i < bytes.length; i++) bytes[i] = Math.floor(Math.random() * 256);
+  bytes[0] ^= now & 0xff;
+  bytes[1] ^= (now >>> 8) & 0xff;
+  bytes[2] ^= (now >>> 16) & 0xff;
+  bytes[3] ^= (now >>> 24) & 0xff;
+  return bytes;
+}
+
+export function generateUUID(cryptoLike: CryptoLike | null = globalThis.crypto): string {
+  if (cryptoLike && typeof cryptoLike.randomUUID === "function") return cryptoLike.randomUUID();
+
+  if (cryptoLike && typeof cryptoLike.getRandomValues === "function") {
+    const bytes = new Uint8Array(16);
+    cryptoLike.getRandomValues(bytes);
+    return uuidFromBytes(bytes);
+  }
+
+  return uuidFromBytes(weakRandomBytes());
+}
+