diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index b25690092..2cdaf6bc7 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -748,9 +748,9 @@ export class Config {
       initializeTelemetry(this);
     }
 
-    const normalizedProxy = normalizeProxyUrl(this.getProxy());
-    if (normalizedProxy) {
-      setGlobalDispatcher(new ProxyAgent(normalizedProxy));
+    const proxyUrl = this.getProxy();
+    if (proxyUrl) {
+      setGlobalDispatcher(new ProxyAgent(proxyUrl));
     }
     this.geminiClient = new GeminiClient(this);
     this.chatRecordingService = this.chatRecordingEnabled
@@ -1719,7 +1719,7 @@ export class Config {
   }
 
   getProxy(): string | undefined {
-    return this.proxy;
+    return normalizeProxyUrl(this.proxy);
   }
 
   getWorkingDir(): string {
diff --git a/packages/core/src/utils/proxyUtils.test.ts b/packages/core/src/utils/proxyUtils.test.ts
index 7f7a54373..4f971aec5 100644
--- a/packages/core/src/utils/proxyUtils.test.ts
+++ b/packages/core/src/utils/proxyUtils.test.ts
@@ -78,27 +78,28 @@ describe('normalizeProxyUrl', () => {
     expect(normalizeProxyUrl('http://[::1]:8080')).toBe('http://[::1]:8080');
   });
 
-  it('should not modify URL that already has socks:// prefix', () => {
-    expect(normalizeProxyUrl('socks://proxy.example.com:1080')).toBe(
-      'socks://proxy.example.com:1080',
+  // SOCKS proxy tests - should throw error since undici doesn't support SOCKS
+  it('should throw error for socks:// proxy URL', () => {
+    expect(() => normalizeProxyUrl('socks://proxy.example.com:1080')).toThrow(
+      'SOCKS proxy is not supported',
     );
   });
 
-  it('should not modify URL that already has socks4:// prefix', () => {
-    expect(normalizeProxyUrl('socks4://proxy.example.com:1080')).toBe(
-      'socks4://proxy.example.com:1080',
+  it('should throw error for socks4:// proxy URL', () => {
+    expect(() => normalizeProxyUrl('socks4://proxy.example.com:1080')).toThrow(
+      'SOCKS proxy is not supported',
     );
   });
 
-  it('should not modify URL that already has socks5:// prefix', () => {
-    expect(normalizeProxyUrl('socks5://proxy.example.com:1080')).toBe(
-      'socks5://proxy.example.com:1080',
+  it('should throw error for socks5:// proxy URL', () => {
+    expect(() => normalizeProxyUrl('socks5://proxy.example.com:1080')).toThrow(
+      'SOCKS proxy is not supported',
     );
   });
 
-  it('should handle SOCKS:// prefix (case insensitive)', () => {
-    expect(normalizeProxyUrl('SOCKS5://proxy.example.com:1080')).toBe(
-      'SOCKS5://proxy.example.com:1080',
+  it('should throw error for SOCKS5:// proxy URL (case insensitive)', () => {
+    expect(() => normalizeProxyUrl('SOCKS5://proxy.example.com:1080')).toThrow(
+      'SOCKS proxy is not supported',
     );
   });
 });
diff --git a/packages/core/src/utils/proxyUtils.ts b/packages/core/src/utils/proxyUtils.ts
index 30e42654d..322cd5311 100644
--- a/packages/core/src/utils/proxyUtils.ts
+++ b/packages/core/src/utils/proxyUtils.ts
@@ -11,8 +11,13 @@
  * This function adds the "http://" prefix if missing, since HTTP proxies are
  * the most common default.
  *
+ * Note: Only HTTP and HTTPS proxies are supported. SOCKS proxies (socks://,
+ * socks4://, socks5://) are NOT supported because the underlying undici library
+ * does not support them. See: https://github.com/nodejs/undici/issues/2224
+ *
  * @param proxyUrl - The proxy URL to normalize
  * @returns The normalized proxy URL with protocol prefix, or undefined if input is undefined/empty
+ * @throws Error if a SOCKS proxy URL is provided
  */
 export function normalizeProxyUrl(
   proxyUrl: string | undefined,
@@ -27,11 +32,20 @@ export function normalizeProxyUrl(
   }
 
   // Check if the URL already has a protocol prefix
-  // Support http, https, socks, socks4, socks5 protocols
-  if (/^(https?|socks[45]?):\/\//i.test(trimmed)) {
+  // Only support http and https protocols (undici limitation)
+  if (/^https?:\/\//i.test(trimmed)) {
     return trimmed;
   }
 
+  // Reject SOCKS proxies - undici does not support them
+  if (/^socks[45]?:\/\//i.test(trimmed)) {
+    throw new Error(
+      `SOCKS proxy is not supported. The underlying HTTP client (undici) only supports HTTP and HTTPS proxies. ` +
+        `Please use an HTTP/HTTPS proxy instead, or set up a SOCKS-to-HTTP proxy converter. ` +
+        `See: https://github.com/nodejs/undici/issues/2224`,
+    );
+  }
+
   // Add http:// prefix for proxy URLs without protocol
   // HTTP is the default for most proxy configurations
   return `http://${trimmed}`;