diff --git a/src/LLMProviders/BedrockChatModel.ts b/src/LLMProviders/BedrockChatModel.ts
index 32faff84..22c8fabf 100644
--- a/src/LLMProviders/BedrockChatModel.ts
+++ b/src/LLMProviders/BedrockChatModel.ts
@@ -1,3 +1,8 @@
+// Reason: `buffer` is the npm polyfill (browser-compatible), bundled by esbuild
+// so the same Buffer code path works on desktop (Electron) and mobile (WebView).
+// eslint-disable-next-line import/no-nodejs-modules
+import { Buffer } from "buffer";
+
 import {
   BaseChatModel,
   type BaseChatModelCallOptions,
@@ -793,6 +798,8 @@ export class BedrockChatModel extends BaseChatModel<BedrockChatModelCallOptions>
 
   private decodeBase64ToUint8Array(encoded: string): Uint8Array | null {
     try {
+      // Reason: Buffer (from the `buffer` polyfill imported above) is the
+      // cross-platform path — bare global Buffer is undefined in mobile WebView.
       return new Uint8Array(Buffer.from(encoded, "base64"));
     } catch {
       return null;
diff --git a/src/utils.ts b/src/utils.ts
index 58d3de54..2cc2942d 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1,3 +1,8 @@
+// Reason: `buffer` is the npm polyfill (browser-compatible), bundled by esbuild
+// so the same Buffer code path works on desktop (Electron) and mobile (WebView).
+// eslint-disable-next-line import/no-nodejs-modules
+import { Buffer } from "buffer";
+
 import { Document } from "@/chainFactory";
 import { ChainType } from "@/chainType";
 import {
@@ -883,6 +888,8 @@ export async function safeFetch(
         return response.arrayBuffer;
       }
       const base64 = response.text.replace(/^data:.*;base64,/, "");
+      // Reason: Buffer (from the `buffer` polyfill imported above) is the
+      // cross-platform path — bare global Buffer is undefined in mobile WebView.
       const buf = Buffer.from(base64, "base64");
       return buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength) as ArrayBuffer;
     },
diff --git a/src/utils/base64.test.ts b/src/utils/base64.test.ts
new file mode 100644
index 00000000..b52ee559
--- /dev/null
+++ b/src/utils/base64.test.ts
@@ -0,0 +1,37 @@
+import { arrayBufferToBase64, base64ToArrayBuffer } from "./base64";
+
+describe("base64 utils", () => {
+  it("round-trips a small ArrayBuffer", () => {
+    const original = new Uint8Array([0, 1, 2, 3, 127, 128, 255]).buffer;
+    const encoded = arrayBufferToBase64(original);
+    const decoded = base64ToArrayBuffer(encoded);
+    expect(new Uint8Array(decoded)).toEqual(new Uint8Array(original));
+  });
+
+  it("matches a known base64 fixture", () => {
+    const bytes = new TextEncoder().encode("Copilot 🚀");
+    expect(arrayBufferToBase64(bytes.buffer as ArrayBuffer)).toBe("Q29waWxvdCDwn5qA");
+  });
+
+  // Reason: regression guard for the 3.3.0 mobile bug. Mobile Obsidian's
+  // WebView runtime has no Node.js globals — bare `Buffer` is undefined.
+  // The helpers must import Buffer from the `buffer` npm polyfill (bundled
+  // by esbuild) and not rely on `globalThis.Buffer`. This test deletes the
+  // global to make sure the imported binding is what's actually being used.
+  it("works without relying on globalThis.Buffer (mobile WebView simulation)", () => {
+    // eslint-disable-next-line obsidianmd/no-global-this -- jsdom test needs to mutate the actual global runtime, not a per-window scope
+    const g = globalThis as { Buffer?: unknown };
+    const originalBuffer = g.Buffer;
+    try {
+      delete g.Buffer;
+      const bytes = new Uint8Array([10, 20, 30, 40]).buffer;
+      const encoded = arrayBufferToBase64(bytes);
+      const decoded = base64ToArrayBuffer(encoded);
+      expect(new Uint8Array(decoded)).toEqual(new Uint8Array(bytes));
+    } finally {
+      if (originalBuffer !== undefined) {
+        g.Buffer = originalBuffer;
+      }
+    }
+  });
+});
diff --git a/src/utils/base64.ts b/src/utils/base64.ts
index 71f0bfdb..818143e5 100644
--- a/src/utils/base64.ts
+++ b/src/utils/base64.ts
@@ -1,7 +1,16 @@
+// Reason: explicit import from the `buffer` npm polyfill (a browser-compatible
+// drop-in, not a runtime use of Node's built-in). Mobile Obsidian's WebView has
+// no Node globals, so bare `Buffer` throws "Can't find variable: Buffer" on iOS
+// WebKit. esbuild bundles this polyfill into main.js so the same code path
+// works on both desktop and mobile.
+// eslint-disable-next-line import/no-nodejs-modules
+import { Buffer } from "buffer";
+
 export function arrayBufferToBase64(buffer: ArrayBuffer): string {
   return Buffer.from(buffer).toString("base64");
 }
 
 export function base64ToArrayBuffer(base64: string): ArrayBuffer {
-  return new Uint8Array(Buffer.from(base64, "base64")).buffer;
+  const buf = Buffer.from(base64, "base64");
+  return buf.buffer.slice(buf.byteOffset, buf.byteOffset + buf.byteLength) as ArrayBuffer;
 }