fix(proxy): omit bracketed [::1] from child process NO_PROXY

.changeset/fix-child-no-proxy-bracketed-ipv6.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix stdio MCP servers (Python httpx-based) crashing with `httpx.InvalidURL` when a proxy is configured. The bracketed `[::1]` loopback entry is no longer injected into child process `NO_PROXY`; only the bare `::1` is used, which all major HTTP client libraries parse correctly.

packages/agent-core-v2/src/_base/utils/proxy.ts

@@ -1,6 +1,10 @@
 /**
  * Resolve and install proxy configuration for outbound `fetch` and spawned
  * child processes (HTTP/HTTPS and SOCKS, honoring `NO_PROXY`).
+ *
+ * Child NO_PROXY is runtime-aware: Node children (undici) require the bracketed
+ * `[::1]` loopback entry, while non-Node children (Python httpx, Go) crash on
+ * it and only accept bare `::1` (#1931).
  */
 
 import {
@@ -23,6 +27,7 @@ export interface SocksProxyConfig {
 }
 
 const LOOPBACK_NO_PROXY = ['localhost', '127.0.0.1', '::1', '[::1]'] as const;
+const LOOPBACK_NO_PROXY_NON_NODE_CHILD = ['localhost', '127.0.0.1', '::1'] as const;
 
 const SOCKS_SCHEMES = new Set(['socks', 'socks4', 'socks4a', 'socks5', 'socks5h']);
 
@@ -91,13 +96,21 @@ export function isProxyConfigured(env: Env): boolean {
 }
 
 export function resolveNoProxy(env: Env): string {
+  return resolveNoProxyWith(env, LOOPBACK_NO_PROXY);
+}
+
+export function resolveNoProxyForChild(env: Env, isNodeRuntime = false): string {
+  return resolveNoProxyWith(env, isNodeRuntime ? LOOPBACK_NO_PROXY : LOOPBACK_NO_PROXY_NON_NODE_CHILD);
+}
+
+function resolveNoProxyWith(env: Env, loopbacks: readonly string[]): string {
   const raw = [env['no_proxy'], env['NO_PROXY']].find((value) => (value?.trim() ?? '').length > 0) ?? '';
   const hosts = raw
     .split(',')
     .map((host) => host.trim())
     .filter((host) => host.length > 0);
   if (hosts.includes('*')) return '*';
-  for (const loopback of LOOPBACK_NO_PROXY) {
+  for (const loopback of loopbacks) {
     if (!hosts.includes(loopback)) hosts.push(loopback);
   }
   return hosts.join(',');
@@ -230,9 +243,9 @@ export function installGlobalProxyDispatcher(
   return true;
 }
 
-export function proxyEnvForChild(env: Env): Record<string, string> {
+export function proxyEnvForChild(env: Env, isNodeRuntime = false): Record<string, string> {
   if (!hasHttpProxy(env)) return {};
-  const noProxy = resolveNoProxy(env);
+  const noProxy = resolveNoProxyForChild(env, isNodeRuntime);
   const result: Record<string, string> = {
     NODE_USE_ENV_PROXY: '1',
     NO_PROXY: noProxy,
@@ -253,12 +266,13 @@ export function proxyEnvForChild(env: Env): Record<string, string> {
 export function reconcileChildNoProxy(
   childEnv: Record<string, string>,
   configEnv?: Record<string, string>,
+  isNodeRuntime = false,
 ): void {
   const override = [configEnv?.['no_proxy'], configEnv?.['NO_PROXY']].find(
     (value) => (value?.trim() ?? '').length > 0,
   );
   if (override === undefined) return;
-  const noProxy = resolveNoProxy({ no_proxy: override, NO_PROXY: override });
+  const noProxy = resolveNoProxyForChild({ no_proxy: override, NO_PROXY: override }, isNodeRuntime);
   childEnv['NO_PROXY'] = noProxy;
   childEnv['no_proxy'] = noProxy;
 }

packages/agent-core-v2/src/agent/mcp/client-stdio.ts

@@ -50,7 +50,7 @@ export class StdioMcpClient implements MCPClient {
     this.transport = new StdioClientTransport({
       command: config.command,
       args: config.args,
-      env: mergeStdioEnv(config.env),
+      env: mergeStdioEnv(config.env, undefined, config.command),
       cwd: resolveStdioCwd(config.cwd, options.defaultCwd),
       stderr: 'pipe',
     });
@@ -184,13 +184,22 @@ function resolveStdioCwd(configCwd: string | undefined, defaultCwd: string | und
 export function mergeStdioEnv(
   configEnv?: Record<string, string>,
   parentEnv: Readonly<Record<string, string | undefined>> = process.env,
+  command?: string,
 ): Record<string, string> {
   const merged: Record<string, string> = {};
   for (const [key, value] of Object.entries(parentEnv)) {
     if (value !== undefined) merged[key] = value;
   }
   if (configEnv !== undefined) Object.assign(merged, configEnv);
-  Object.assign(merged, proxyEnvForChild(merged));
-  reconcileChildNoProxy(merged, configEnv);
+  const isNode = isNodeCommand(command);
+  Object.assign(merged, proxyEnvForChild(merged, isNode));
+  reconcileChildNoProxy(merged, configEnv, isNode);
   return merged;
 }
+
+/** True when the command is a Node.js runtime (node, npx, tsx, etc.). */
+function isNodeCommand(command?: string): boolean {
+  if (command === undefined) return false;
+  const base = command.replaceAll('\\', '/').split('/').pop()?.replace(/\.(exe|cmd|bat)$/i, '').toLowerCase();
+  return base === 'node' || base === 'npx' || base === 'tsx' || base === 'ts-node';
+}

packages/agent-core-v2/test/_base/utils/proxy.test.ts

@@ -130,8 +130,8 @@ describe('proxy utilities', () => {
     expect(proxyEnvForChild({ ALL_PROXY: 'socks5://127.0.0.1:1080' })).toEqual({});
     expect(proxyEnvForChild({ HTTP_PROXY: 'http://p:3128', NO_PROXY: 'corp' })).toEqual({
       NODE_USE_ENV_PROXY: '1',
-      NO_PROXY: 'corp,localhost,127.0.0.1,::1,[::1]',
-      no_proxy: 'corp,localhost,127.0.0.1,::1,[::1]',
+      NO_PROXY: 'corp,localhost,127.0.0.1,::1',
+      no_proxy: 'corp,localhost,127.0.0.1,::1',
       HTTP_PROXY: 'http://p:3128',
       http_proxy: 'http://p:3128',
     });
@@ -141,7 +141,7 @@ describe('proxy utilities', () => {
       no_proxy: 'aug',
     };
     reconcileChildNoProxy(childEnv, { no_proxy: '', NO_PROXY: 'real.corp' });
-    expect(childEnv['NO_PROXY']).toBe('real.corp,localhost,127.0.0.1,::1,[::1]');
-    expect(childEnv['no_proxy']).toBe('real.corp,localhost,127.0.0.1,::1,[::1]');
+    expect(childEnv['NO_PROXY']).toBe('real.corp,localhost,127.0.0.1,::1');
+    expect(childEnv['no_proxy']).toBe('real.corp,localhost,127.0.0.1,::1');
   });
 });

packages/agent-core-v2/test/agent/mcp/client-stdio.test.ts

@@ -304,7 +304,7 @@ describe('mergeStdioEnv', () => {
     const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' });
     expect(merged['HTTP_PROXY']).toBe('http://corp:3128');
     expect(merged['NODE_USE_ENV_PROXY']).toBe('1');
-    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1,[::1]');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1');
     expect(merged['PATH']).toBe('/usr/bin');
   });
 
@@ -324,4 +324,14 @@ describe('mergeStdioEnv', () => {
     await rm(dir, { recursive: true, force: true });
     expect(mergeStdioEnv(undefined, { PATH: dir })['PATH']).toBe(dir);
   });
+
+  it('preserves bracketed [::1] in NO_PROXY for a Node child command', () => {
+    const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' }, 'node');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1,[::1]');
+  });
+
+  it('omits bracketed [::1] in NO_PROXY for a non-Node child command', () => {
+    const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' }, 'python');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1');
+  });
 });

packages/agent-core/src/mcp/client-stdio.ts

@@ -65,7 +65,7 @@ export class StdioMcpClient implements MCPClient {
     this.transport = new StdioClientTransport({
       command: config.command,
       args: config.args,
-      env: mergeStdioEnv(config.env),
+      env: mergeStdioEnv(config.env, undefined, config.command),
       cwd: resolveStdioCwd(config.cwd, options.defaultCwd),
       stderr: 'pipe',
     });
@@ -256,13 +256,22 @@ function isWindowsAbsolutePath(value: string): boolean {
 export function mergeStdioEnv(
   configEnv?: Record<string, string>,
   parentEnv: Readonly<Record<string, string | undefined>> = process.env,
+  command?: string,
 ): Record<string, string> {
   const merged: Record<string, string> = {};
   for (const [key, value] of Object.entries(parentEnv)) {
     if (value !== undefined) merged[key] = value;
   }
   if (configEnv !== undefined) Object.assign(merged, configEnv);
-  Object.assign(merged, proxyEnvForChild(merged));
-  reconcileChildNoProxy(merged, configEnv);
+  const isNode = isNodeCommand(command);
+  Object.assign(merged, proxyEnvForChild(merged, isNode));
+  reconcileChildNoProxy(merged, configEnv, isNode);
   return merged;
 }
+
+/** True when the command is a Node.js runtime (node, npx, tsx, etc.). */
+function isNodeCommand(command?: string): boolean {
+  if (command === undefined) return false;
+  const base = command.replaceAll('\\', '/').split('/').pop()?.replace(/\.(exe|cmd|bat)$/i, '').toLowerCase();
+  return base === 'node' || base === 'npx' || base === 'tsx' || base === 'ts-node';
+}

packages/agent-core/src/utils/proxy.ts

@@ -30,6 +30,13 @@ export interface SocksProxyConfig {
 // normalizes brackets away — so including both covers every path.
 const LOOPBACK_NO_PROXY = ['localhost', '127.0.0.1', '::1', '[::1]'] as const;
 
+// Child processes (e.g. stdio MCP servers) must NOT receive the bracketed `[::1]`:
+// Non-Node child processes (e.g. Python stdio MCP servers) must NOT receive the
+// bracketed `[::1]`: Python's httpx parses `all://[::1]` and treats `:1]` as the
+// port, raising `httpx.InvalidURL`. Node children (with NODE_USE_ENV_PROXY=1)
+// still need the bracketed form because undici mis-parses bare `::1`.
+const LOOPBACK_NO_PROXY_NON_NODE_CHILD = ['localhost', '127.0.0.1', '::1'] as const;
+
 const SOCKS_SCHEMES = new Set(['socks', 'socks4', 'socks4a', 'socks5', 'socks5h']);
 
 /** Lowercase URL scheme (without the trailing colon), or undefined if absent. */
@@ -130,6 +137,22 @@ export function isProxyConfigured(env: Env = process.env): boolean {
  * through the proxy.
  */
 export function resolveNoProxy(env: Env = process.env): string {
+  return resolveNoProxyWith(env, LOOPBACK_NO_PROXY);
+}
+
+/**
+ * Like {@link resolveNoProxy} but selects the loopback list based on the child
+ * runtime. Node children (undici via NODE_USE_ENV_PROXY) need the bracketed
+ * `[::1]`; non-Node children (Python httpx, Go, etc.) crash on it and only
+ * accept bare `::1`.
+ *
+ * @see https://github.com/MoonshotAI/kimi-code/issues/1931
+ */
+export function resolveNoProxyForChild(env: Env = process.env, isNodeRuntime = false): string {
+  return resolveNoProxyWith(env, isNodeRuntime ? LOOPBACK_NO_PROXY : LOOPBACK_NO_PROXY_NON_NODE_CHILD);
+}
+
+function resolveNoProxyWith(env: Env, loopbacks: readonly string[]): string {
   // Prefer the first non-blank casing; an empty `no_proxy=''` must not mask a
   // populated `NO_PROXY` (`??` would, since `''` is not nullish).
   const raw = [env['no_proxy'], env['NO_PROXY']].find((value) => (value?.trim() ?? '').length > 0) ?? '';
@@ -138,7 +161,7 @@ export function resolveNoProxy(env: Env = process.env): string {
     .map((host) => host.trim())
     .filter((host) => host.length > 0);
   if (hosts.includes('*')) return '*';
-  for (const loopback of LOOPBACK_NO_PROXY) {
+  for (const loopback of loopbacks) {
     if (!hosts.includes(loopback)) hosts.push(loopback);
   }
   return hosts.join(',');
@@ -333,9 +356,9 @@ export function installGlobalProxyDispatcher(
  * an http-scheme `ALL_PROXY` is synthesized into the scheme-specific variables
  * so an `ALL_PROXY`-only parent still proxies the child.
  */
-export function proxyEnvForChild(env: Env = process.env): Record<string, string> {
+export function proxyEnvForChild(env: Env = process.env, isNodeRuntime = false): Record<string, string> {
   if (!hasHttpProxy(env)) return {};
-  const noProxy = resolveNoProxy(env);
+  const noProxy = resolveNoProxyForChild(env, isNodeRuntime);
   const result: Record<string, string> = {
     NODE_USE_ENV_PROXY: '1',
     NO_PROXY: noProxy,
@@ -361,18 +384,19 @@ export function proxyEnvForChild(env: Env = process.env): Record<string, string>
  *
  * Uses the first NON-blank casing (a blank `no_proxy=''` must not mask a
  * populated `NO_PROXY`, mirroring {@link resolveNoProxy}) and runs the value
- * back through {@link resolveNoProxy} so the loopback bypass is preserved and
+ * back through {@link resolveNoProxyForChild} so the loopback bypass is preserved and
  * `*` passes through verbatim. No-op when config sets no usable `NO_PROXY`.
  */
 export function reconcileChildNoProxy(
   childEnv: Record<string, string>,
   configEnv?: Record<string, string>,
+  isNodeRuntime = false,
 ): void {
   const override = [configEnv?.['no_proxy'], configEnv?.['NO_PROXY']].find(
     (value) => (value?.trim() ?? '').length > 0,
   );
   if (override === undefined) return;
-  const noProxy = resolveNoProxy({ no_proxy: override, NO_PROXY: override });
+  const noProxy = resolveNoProxyForChild({ no_proxy: override, NO_PROXY: override }, isNodeRuntime);
   childEnv['NO_PROXY'] = noProxy;
   childEnv['no_proxy'] = noProxy;
 }

packages/agent-core/test/mcp/client-stdio.test.ts

@@ -315,7 +315,7 @@ describe('mergeStdioEnv', () => {
     const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' });
     expect(merged['HTTP_PROXY']).toBe('http://corp:3128');
     expect(merged['NODE_USE_ENV_PROXY']).toBe('1');
-    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1,[::1]');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1');
     expect(merged['PATH']).toBe('/usr/bin');
   });
 
@@ -329,4 +329,14 @@ describe('mergeStdioEnv', () => {
     const merged = mergeStdioEnv({ FOO: 'override' }, { FOO: 'parent', PATH: '/x' });
     expect(merged['FOO']).toBe('override');
   });
+
+  it('preserves bracketed [::1] in NO_PROXY for a Node child command', () => {
+    const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' }, 'node');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1,[::1]');
+  });
+
+  it('omits bracketed [::1] in NO_PROXY for a non-Node child command', () => {
+    const merged = mergeStdioEnv({ HTTP_PROXY: 'http://corp:3128' }, { PATH: '/usr/bin' }, 'python');
+    expect(merged['NO_PROXY']).toBe('localhost,127.0.0.1,::1');
+  });
 });

packages/agent-core/test/utils/proxy.test.ts

@@ -343,8 +343,8 @@ describe('proxyEnvForChild', () => {
     // the resolved value or the protection/proxying is silently defeated.
     expect(proxyEnvForChild({ HTTP_PROXY: 'http://p:3128', NO_PROXY: 'corp' })).toEqual({
       NODE_USE_ENV_PROXY: '1',
-      NO_PROXY: 'corp,localhost,127.0.0.1,::1,[::1]',
-      no_proxy: 'corp,localhost,127.0.0.1,::1,[::1]',
+      NO_PROXY: 'corp,localhost,127.0.0.1,::1',
+      no_proxy: 'corp,localhost,127.0.0.1,::1',
       HTTP_PROXY: 'http://p:3128',
       http_proxy: 'http://p:3128',
     });
@@ -355,8 +355,8 @@ describe('proxyEnvForChild', () => {
     // ALL_PROXY-only parent must hand the child the scheme-specific vars.
     expect(proxyEnvForChild({ ALL_PROXY: 'http://proxy:8080' })).toEqual({
       NODE_USE_ENV_PROXY: '1',
-      NO_PROXY: 'localhost,127.0.0.1,::1,[::1]',
-      no_proxy: 'localhost,127.0.0.1,::1,[::1]',
+      NO_PROXY: 'localhost,127.0.0.1,::1',
+      no_proxy: 'localhost,127.0.0.1,::1',
       HTTP_PROXY: 'http://proxy:8080',
       http_proxy: 'http://proxy:8080',
       HTTPS_PROXY: 'http://proxy:8080',
@@ -385,32 +385,32 @@ describe('reconcileChildNoProxy', () => {
     // would shadow the server config's uppercase override (undici reads
     // lowercase first); the override must also keep the loopback bypass.
     const childEnv: Record<string, string> = {
-      NO_PROXY: 'corp,localhost,127.0.0.1,::1,[::1]',
-      no_proxy: 'corp,localhost,127.0.0.1,::1,[::1]',
+      NO_PROXY: 'corp,localhost,127.0.0.1,::1',
+      no_proxy: 'corp,localhost,127.0.0.1,::1',
     };
     reconcileChildNoProxy(childEnv, { NO_PROXY: 'server.local' });
-    expect(childEnv['NO_PROXY']).toBe('server.local,localhost,127.0.0.1,::1,[::1]');
-    expect(childEnv['no_proxy']).toBe('server.local,localhost,127.0.0.1,::1,[::1]');
+    expect(childEnv['NO_PROXY']).toBe('server.local,localhost,127.0.0.1,::1');
+    expect(childEnv['no_proxy']).toBe('server.local,localhost,127.0.0.1,::1');
   });
 
   it('prefers the first non-blank casing (lowercase) and keeps loopback', () => {
     const childEnv: Record<string, string> = { NO_PROXY: 'aug', no_proxy: 'aug' };
     reconcileChildNoProxy(childEnv, { no_proxy: 'lower', NO_PROXY: 'upper' });
-    expect(childEnv['NO_PROXY']).toBe('lower,localhost,127.0.0.1,::1,[::1]');
-    expect(childEnv['no_proxy']).toBe('lower,localhost,127.0.0.1,::1,[::1]');
+    expect(childEnv['NO_PROXY']).toBe('lower,localhost,127.0.0.1,::1');
+    expect(childEnv['no_proxy']).toBe('lower,localhost,127.0.0.1,::1');
   });
 
   it('does not let a blank lowercase no_proxy mask a populated NO_PROXY', () => {
     const childEnv: Record<string, string> = { NO_PROXY: 'aug', no_proxy: 'aug' };
     reconcileChildNoProxy(childEnv, { no_proxy: '', NO_PROXY: 'real.corp' });
-    expect(childEnv['NO_PROXY']).toBe('real.corp,localhost,127.0.0.1,::1,[::1]');
-    expect(childEnv['no_proxy']).toBe('real.corp,localhost,127.0.0.1,::1,[::1]');
+    expect(childEnv['NO_PROXY']).toBe('real.corp,localhost,127.0.0.1,::1');
+    expect(childEnv['no_proxy']).toBe('real.corp,localhost,127.0.0.1,::1');
   });
 
   it('passes the "*" wildcard override through verbatim', () => {
     const childEnv: Record<string, string> = {
-      NO_PROXY: 'corp,localhost,127.0.0.1,::1,[::1]',
-      no_proxy: 'corp,localhost,127.0.0.1,::1,[::1]',
+      NO_PROXY: 'corp,localhost,127.0.0.1,::1',
+      no_proxy: 'corp,localhost,127.0.0.1,::1',
     };
     reconcileChildNoProxy(childEnv, { NO_PROXY: '*' });
     expect(childEnv['NO_PROXY']).toBe('*');