fix base64 build issue (#4581)

* fix base64 build issue

* remove leading whitespace

* fix import

* add explanation

---------

Co-authored-by: Luke Taylor <service@lukebtaylor.com>

packages/local-mail-watcher/Dockerfile

@@ -1,4 +1,4 @@
- FROM node:22.12 as builder
+FROM node:22.12 as builder
 
 WORKDIR /app
 

packages/local-mail-watcher/src/lib/base64.js

@@ -1,19 +0,0 @@
-/**
- * Utility functions for handling base64 encoding/decoding
- */
-
-/**
- * Decodes a base64 string to UTF-8 text
- * Uses Node.js Buffer but with type safety
- */
-export function decodeBase64(base64String: string): string {
-    try {
-      // Use a type-safe approach without relying on global
-      // @ts-ignore - Ignore TypeScript error for Buffer
-      return Buffer.from(base64String, 'base64').toString('utf-8');
-    } catch (error) {
-      console.error('Error decoding base64 string:', error);
-      return base64String; // Return original string if decoding fails
-    }
-  }
-  

packages/local-mail-watcher/src/lib/base64.ts

@@ -0,0 +1,21 @@
+/**
+ * Utility functions for handling base64 encoding/decoding
+ */
+
+// Node.js Buffer is globally available
+// Only import type information - no runtime import
+// This will be removed during compilation
+import type {} from '../types/node-buffer';
+
+/**
+ * Decodes a base64 string to UTF-8 text
+ * Uses Node.js Buffer with type safety
+ */
+export function decodeBase64(base64String: string): string {
+  try {
+    return Buffer.from(base64String, 'base64').toString('utf-8');
+  } catch (error) {
+    console.error('Error decoding base64 string:', error);
+    return base64String; // Return original string if decoding fails
+  }
+}

packages/local-mail-watcher/src/lib/node-buffer.d.ts

@@ -0,0 +1,23 @@
+declare global {
+  interface Buffer extends Uint8Array {
+    write(string: string, encoding?: BufferEncoding): number;
+    toString(encoding?: BufferEncoding, start?: number, end?: number): string;
+  }
+
+  interface BufferConstructor {
+    from(arrayBuffer: WithImplicitCoercion<ArrayBuffer | SharedArrayBuffer>, byteOffset?: number, length?: number): Buffer;
+    from(data: WithImplicitCoercion<Uint8Array | readonly number[]>): Buffer;
+    from(str: WithImplicitCoercion<string>, encoding?: BufferEncoding): Buffer;
+    alloc(size: number): Buffer;
+    alloc(size: number, fill: string | Buffer | number): Buffer;
+  }
+
+  type WithImplicitCoercion<T> = T | { valueOf(): T };
+
+  type BufferEncoding = 'ascii' | 'utf8' | 'utf-8' | 'utf16le' | 'ucs2' | 'ucs-2' | 'base64' | 'latin1' | 'binary' | 'hex';
+
+  const Buffer: BufferConstructor;
+}
+
+// This empty export makes TypeScript treat this file as a module
+export {};