diff --git a/packages/core/src/agent.ts b/packages/core/src/agent.ts
index cf60604..64d7c8c 100644
--- a/packages/core/src/agent.ts
+++ b/packages/core/src/agent.ts
@@ -76,6 +76,16 @@ export interface CreateAgentOptions {
   projectId?: string;
   /** Local data root directory; defaults to `resolveRoot()` (PENGUIN_HOME or ~/.penguin/data). */
   root?: string;
+  /**
+   * When it returns true, the proxy variables (HTTP_PROXY / HTTPS_PROXY / ALL_PROXY;
+   * NO_PROXY is kept) are stripped from exec_command subprocess environments of every
+   * Session this Agent creates or resumes — and of its subagents' Sessions, which
+   * inherit the getter. The Web server threads its admin-level "use system HTTP proxy"
+   * switch (off state) through here; the getter is re-read at every command spawn, so a
+   * toggle needs no restart. Absent = proxy allowed (SDK/CLI standalone use follows the
+   * user's own shell environment).
+   */
+  stripProxyEnv?: () => boolean;
 }
 
 export interface CreateSessionOptions {
@@ -149,13 +159,15 @@ export function metaMaxTokens(budget: number, modelCap: number | undefined): num
 export async function createAgent(opts: CreateAgentOptions = {}): Promise<Agent> {
   const state = await loadOrInitAgentState(opts);
   const projectConfig = await loadProjectConfig(state.root, state.projectId);
-  return new Agent(state, projectConfig);
+  return new Agent(state, projectConfig, opts.stripProxyEnv);
 }
 
 export class Agent {
   constructor(
     readonly state: AgentState,
     readonly projectConfig: ProjectConfig,
+    /** See {@link CreateAgentOptions.stripProxyEnv}; forwarded into every Session's Environment. */
+    private readonly stripProxyEnv?: () => boolean,
   ) {}
 
   /**
@@ -582,7 +594,15 @@ export class Agent {
         }
         const childAgent =
           agentId !== undefined && agentId !== parentAgentId
-            ? await createAgent({ root, projectId, agentId })
+            ? await createAgent({
+                root,
+                projectId,
+                agentId,
+                // A child Agent loads its own vault/config, but the proxy-strip getter is
+                // host policy, not Agent state: the subagent's commands run in the same
+                // serving process, so they follow the same switch as the parent's.
+                ...(parentAgent.stripProxyEnv ? { stripProxyEnv: parentAgent.stripProxyEnv } : {}),
+              })
             : parentAgent;
         // The child Session follows the PARENT Session, never the Project default: with the
         // model pair fully omitted it reuses the parent's resolved (provider, model_id) —
@@ -724,6 +744,7 @@ export class Agent {
       ),
       services: { subagentRunner, ...(visionDescriber ? { visionDescriber } : {}) },
       ...(Object.keys(vault).length > 0 ? { vault } : {}),
+      ...(this.stripProxyEnv ? { stripProxyEnv: this.stripProxyEnv } : {}),
     });
     const tools = await environment.listTools();
 
diff --git a/packages/core/src/environment/environment.ts b/packages/core/src/environment/environment.ts
index f1fffeb..8cb4d0b 100644
--- a/packages/core/src/environment/environment.ts
+++ b/packages/core/src/environment/environment.ts
@@ -110,10 +110,11 @@ export class Environment implements EnvironmentInterface {
     // The background session registry is created alongside Environment (one per Session) and
     // injected into whichever tools need it; all sessions are finalized together on dispose.
     // The vault environment variables are injected into child processes by the command session
-    // registry at spawn time.
-    this.commandSessions = new CommandSessionManager(
-      config.vault !== undefined ? { vault: config.vault } : {},
-    );
+    // registry at spawn time (which also strips the proxy variables while stripProxyEnv says so).
+    this.commandSessions = new CommandSessionManager({
+      ...(config.vault !== undefined ? { vault: config.vault } : {}),
+      ...(config.stripProxyEnv !== undefined ? { stripProxyEnv: config.stripProxyEnv } : {}),
+    });
     this.subagentSessions = new SubagentSessionManager();
     const services = {
       ...config.services,
diff --git a/packages/core/src/environment/tools/command/session-manager.ts b/packages/core/src/environment/tools/command/session-manager.ts
index c366414..f74b215 100644
--- a/packages/core/src/environment/tools/command/session-manager.ts
+++ b/packages/core/src/environment/tools/command/session-manager.ts
@@ -85,15 +85,29 @@ const STRIPPED_ENV_KEYS = new Set([
   "PENGUIN_SEED_ADMIN_PASSWORD",
 ]);
 
-/** The host environment minus {@link STRIPPED_ENV_KEYS}. */
-function hostEnvForChild(): NodeJS.ProcessEnv {
+/**
+ * Proxy variables removed IN ADDITION when the host asks for it (`stripProxyEnv`, see
+ * {@link CommandSessionManager}): the Web server's "use system HTTP proxy" switch in the
+ * off state must keep commands from inheriting the serving process's proxy environment
+ * (design § "出网与系统代理"). NO_PROXY is deliberately NOT stripped — with no proxy
+ * variables left it is inert, and removing it would change behavior for commands that
+ * set their own proxy. Matched case-insensitively like {@link STRIPPED_ENV_KEYS}, which
+ * also covers the conventional lowercase spellings (http_proxy etc.).
+ */
+const PROXY_ENV_KEYS = new Set(["HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY"]);
+
+/** The host environment minus {@link STRIPPED_ENV_KEYS} (and {@link PROXY_ENV_KEYS} when asked). */
+function hostEnvForChild(stripProxy: boolean): NodeJS.ProcessEnv {
   const env: NodeJS.ProcessEnv = {};
   // Matched case-insensitively rather than deleting the upper-case spellings: Windows resolves
   // environment names without regard to case but stores whatever casing was written, so a
   // `set Port=3000` before `penguin web` would survive a `delete env.PORT` and still reach the
   // child as PORT. On POSIX the two are distinct names and only the exact one exists.
   for (const [key, value] of Object.entries(process.env)) {
-    if (!STRIPPED_ENV_KEYS.has(key.toUpperCase())) env[key] = value;
+    const name = key.toUpperCase();
+    if (STRIPPED_ENV_KEYS.has(name)) continue;
+    if (stripProxy && PROXY_ENV_KEYS.has(name)) continue;
+    env[key] = value;
   }
   return env;
 }
@@ -106,9 +120,17 @@ export class CommandSessionManager {
 
   /** Agent vault environment variables: injected into the child process on every spawn (values never enter the model context, only the environment). */
   private readonly vault: Record<string, string>;
+  /**
+   * When it returns true, {@link PROXY_ENV_KEYS} are removed from the child environment
+   * too. A getter rather than a boolean: the hosting server's "use system HTTP proxy"
+   * switch is toggled at runtime, and re-reading at every spawn makes the toggle reach
+   * Sessions that are already running. Absent = proxy allowed (SDK/CLI standalone use).
+   */
+  private readonly stripProxyEnv: (() => boolean) | undefined;
 
-  constructor(opts?: { vault?: Record<string, string> }) {
+  constructor(opts?: { vault?: Record<string, string>; stripProxyEnv?: () => boolean }) {
     this.vault = opts?.vault ?? {};
+    this.stripProxyEnv = opts?.stripProxyEnv;
   }
 
   /** Starts a command, returning an **unregistered** session (no process_id yet). */
@@ -122,9 +144,10 @@ export class CommandSessionManager {
       // Spread order is priority: vault overrides host variables of the same name, but must
       // come before HARDENED_ENV — the hardening entries (GIT_EDITOR/PAGER etc. that prevent
       // interactive hangs) must never be overridable by vault. The host side is stripped of
-      // the harness's own variables first (see STRIPPED_ENV_KEYS); the vault still wins, so a
-      // user who genuinely wants PORT in commands can set it there.
-      env: { ...hostEnvForChild(), ...this.vault, ...HARDENED_ENV },
+      // the harness's own variables first (see STRIPPED_ENV_KEYS; plus the proxy variables
+      // when stripProxyEnv says so); the vault still wins, so a user who genuinely wants
+      // PORT — or a proxy — in commands can set it there.
+      env: { ...hostEnvForChild(this.stripProxyEnv?.() === true), ...this.vault, ...HARDENED_ENV },
     });
   }
 
diff --git a/packages/core/src/interfaces.ts b/packages/core/src/interfaces.ts
index 7d2d250..88d403b 100644
--- a/packages/core/src/interfaces.ts
+++ b/packages/core/src/interfaces.ts
@@ -292,6 +292,14 @@ export interface EnvironmentConfig {
    * environment; hardened entries cannot be overridden.
    */
   vault?: Record<string, string>;
+  /**
+   * When it returns true, the proxy variables (HTTP_PROXY / HTTPS_PROXY / ALL_PROXY, any
+   * casing; NO_PROXY is kept) are stripped from exec_command / input_command subprocess
+   * environments. Threaded by the Web server from its admin-level "use system HTTP proxy"
+   * switch (off state); re-read at every spawn so a toggle needs no restart. Absent =
+   * proxy allowed (the default for SDK/CLI standalone use).
+   */
+  stripProxyEnv?: () => boolean;
 }
 
 /**
diff --git a/packages/core/test/exec-session.test.ts b/packages/core/test/exec-session.test.ts
index 4596164..3bb69c6 100644
--- a/packages/core/test/exec-session.test.ts
+++ b/packages/core/test/exec-session.test.ts
@@ -406,3 +406,71 @@ describe("harness environment variables never reach a spawned command", () => {
     }
   });
 });
+
+describe("proxy variables are stripped from commands when the host opts out", () => {
+  // The Web server's "use system HTTP proxy" switch (off state) threads stripProxyEnv
+  // through Agent -> Environment -> CommandSessionManager; standalone Environments (no
+  // getter) keep the historical pass-through.
+  const KEYS = ["HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY", "NO_PROXY"] as const;
+  const saved: Partial<Record<(typeof KEYS)[number], string | undefined>> = {};
+  let strip = true;
+  let stripEnv: Environment;
+
+  beforeEach(() => {
+    for (const k of KEYS) saved[k] = process.env[k];
+    process.env.HTTP_PROXY = "http://proxy.corp.example:8080";
+    process.env.HTTPS_PROXY = "http://proxy.corp.example:8443";
+    process.env.ALL_PROXY = "socks5://proxy.corp.example:1080";
+    process.env.NO_PROXY = "localhost,127.0.0.1,::1";
+    strip = true;
+    stripEnv = new Environment({
+      workspaceDir: tmp,
+      toolConfig: sessionConfig(),
+      stripProxyEnv: () => strip,
+    });
+  });
+  afterEach(() => {
+    stripEnv.dispose();
+    for (const k of KEYS) {
+      if (saved[k] === undefined) delete process.env[k];
+      else process.env[k] = saved[k];
+    }
+  });
+
+  it("HTTP(S)_PROXY/ALL_PROXY are removed, NO_PROXY stays (inert without them)", async () => {
+    const READ = KEYS.map((k) => `${k}=[' + (process.env.${k} ?? '') + ']`).join(" ");
+    const res = await runTool(stripEnv, "exec_command", {
+      cmd: `node -e "console.log('${READ}')"`,
+    });
+    expect(res.output).toContain(
+      "HTTP_PROXY=[] HTTPS_PROXY=[] ALL_PROXY=[] NO_PROXY=[localhost,127.0.0.1,::1]",
+    );
+  });
+
+  it("a lowercase spelling is stripped too (the conventional POSIX form)", async () => {
+    process.env.https_proxy = "http://proxy.corp.example:8443";
+    try {
+      const res = await runTool(stripEnv, "exec_command", {
+        cmd: `node -e "console.log('s=[' + (process.env.https_proxy ?? '') + ']')"`,
+      });
+      expect(res.output).toContain("s=[]");
+    } finally {
+      delete process.env.https_proxy;
+    }
+  });
+
+  it("the getter is re-read at every spawn, so a live toggle needs no new Environment", async () => {
+    strip = false;
+    const res = await runTool(stripEnv, "exec_command", {
+      cmd: `node -e "console.log('H=[' + (process.env.HTTP_PROXY ?? '') + ']')"`,
+    });
+    expect(res.output).toContain("H=[http://proxy.corp.example:8080]");
+  });
+
+  it("without the getter (SDK/CLI standalone), proxy variables pass through", async () => {
+    const res = await runTool(env, "exec_command", {
+      cmd: `node -e "console.log('H=[' + (process.env.HTTP_PROXY ?? '') + ']')"`,
+    });
+    expect(res.output).toContain("H=[http://proxy.corp.example:8080]");
+  });
+});
diff --git a/packages/desktop/src/os-proxy.ts b/packages/desktop/src/os-proxy.ts
new file mode 100644
index 0000000..4476a33
--- /dev/null
+++ b/packages/desktop/src/os-proxy.ts
@@ -0,0 +1,63 @@
+/**
+ * OS-proxy resolution for the embedded server (design § "出网与系统代理"): on the
+ * desktop, "system proxy" means the real operating-system setting. The shell resolves
+ * it through Electron's resolveProxy when forking the server and injects the result
+ * into the child environment as HTTP_PROXY / HTTPS_PROXY — the server's dispatcher
+ * (and, while the admin switch is on, agent commands) then honor it. Variables already
+ * present in the shell's environment are never overridden (same idiom as
+ * bundledShellEnv): an explicitly configured environment wins over the OS lookup.
+ *
+ * Only the entry point touches Electron, behind a dynamic import; the parsing and the
+ * override check stay pure so they unit-test without an Electron runtime.
+ */
+
+/** The variables injected, with the probe URL whose scheme selects the OS proxy rule. */
+const PROXY_VARS = [
+  { name: "HTTP_PROXY", lower: "http_proxy", probe: "http://example.com/" },
+  { name: "HTTPS_PROXY", lower: "https_proxy", probe: "https://example.com/" },
+] as const;
+
+type ProxyVar = (typeof PROXY_VARS)[number];
+
+/** The proxy variables `env` does not already define (either spelling — those are kept as-is). */
+export function unsetProxyVars(env: NodeJS.ProcessEnv): readonly ProxyVar[] {
+  return PROXY_VARS.filter((v) => env[v.name] === undefined && env[v.lower] === undefined);
+}
+
+/**
+ * Maps one PAC-style resolveProxy result to a proxy URL, or null for "connect
+ * directly". The result is a `;`-separated fallback list ("PROXY host:port; DIRECT");
+ * the first usable entry wins: `PROXY` → http://, `HTTPS` (a proxy reached over TLS) →
+ * https://. `DIRECT` and the SOCKS flavors yield nothing — undici's dispatcher speaks
+ * only HTTP(S) proxies, and injecting a socks:// URL would break every server fetch.
+ */
+export function proxyUrlFromPacResult(result: string): string | null {
+  for (const entry of result.split(";")) {
+    const m = /^\s*(PROXY|HTTPS)\s+(\S+)\s*$/i.exec(entry);
+    if (!m) continue;
+    const scheme = m[1]!.toUpperCase() === "HTTPS" ? "https" : "http";
+    return `${scheme}://${m[2]!}`;
+  }
+  return null;
+}
+
+/**
+ * The proxy environment to add to the server child: the OS resolution of every proxy
+ * variable the shell's own environment leaves unset. Best-effort — any resolution
+ * failure injects nothing (the server then simply sees no proxy configuration).
+ */
+export async function osProxyEnv(): Promise<Record<string, string>> {
+  const wanted = unsetProxyVars(process.env);
+  if (wanted.length === 0) return {};
+  try {
+    const { session } = await import("electron");
+    const env: Record<string, string> = {};
+    for (const v of wanted) {
+      const url = proxyUrlFromPacResult(await session.defaultSession.resolveProxy(v.probe));
+      if (url !== null) env[v.name] = url;
+    }
+    return env;
+  } catch {
+    return {};
+  }
+}
diff --git a/packages/desktop/src/server-process.ts b/packages/desktop/src/server-process.ts
index 0094175..44439b9 100644
--- a/packages/desktop/src/server-process.ts
+++ b/packages/desktop/src/server-process.ts
@@ -11,6 +11,7 @@ import path from "node:path";
 import { fileURLToPath } from "node:url";
 import { app, utilityProcess } from "electron";
 import type { UtilityProcess } from "electron";
+import { osProxyEnv } from "./os-proxy.js";
 import { choosePort, readPreferredPort, rememberPreferredPort } from "./port-memory.js";
 import { appOriginFor, parsePortFile } from "./util.js";
 
@@ -125,6 +126,10 @@ export async function startEmbeddedServer(opts: {
     env: {
       ...process.env,
       ...bundledShellEnv(),
+      // OS proxy settings resolved at fork time (Electron resolveProxy) — only for the
+      // proxy variables the environment leaves unset, never overriding existing values.
+      // The server's "use system HTTP proxy" switch then governs whether they are used.
+      ...(await osProxyEnv()),
       PENGUIN_HOME: opts.dataRoot,
       HOST: "127.0.0.1",
       PORT: String(requestedPort),
diff --git a/packages/desktop/test/os-proxy.test.ts b/packages/desktop/test/os-proxy.test.ts
new file mode 100644
index 0000000..d815d8a
--- /dev/null
+++ b/packages/desktop/test/os-proxy.test.ts
@@ -0,0 +1,46 @@
+/**
+ * Pure-part tests for the OS-proxy injection (no Electron runtime): PAC-result parsing
+ * and the "never override an existing variable" selection.
+ */
+import { describe, expect, it } from "vitest";
+import { proxyUrlFromPacResult, unsetProxyVars } from "../src/os-proxy.js";
+
+describe("proxyUrlFromPacResult", () => {
+  it("maps PROXY to an http:// URL and HTTPS to an https:// URL", () => {
+    expect(proxyUrlFromPacResult("PROXY 127.0.0.1:8888")).toBe("http://127.0.0.1:8888");
+    expect(proxyUrlFromPacResult("HTTPS proxy.corp.example:443")).toBe(
+      "https://proxy.corp.example:443",
+    );
+    expect(proxyUrlFromPacResult("proxy proxy.corp.example:3128")).toBe(
+      "http://proxy.corp.example:3128",
+    );
+  });
+
+  it("takes the first usable entry of a fallback list", () => {
+    expect(proxyUrlFromPacResult("PROXY 10.0.0.1:8080; DIRECT")).toBe("http://10.0.0.1:8080");
+    expect(proxyUrlFromPacResult("DIRECT; PROXY 10.0.0.1:8080")).toBe("http://10.0.0.1:8080");
+  });
+
+  it("yields nothing for DIRECT and for SOCKS entries (undici cannot speak SOCKS)", () => {
+    expect(proxyUrlFromPacResult("DIRECT")).toBeNull();
+    expect(proxyUrlFromPacResult("SOCKS5 127.0.0.1:1080")).toBeNull();
+    expect(proxyUrlFromPacResult("SOCKS 127.0.0.1:1080; DIRECT")).toBeNull();
+    expect(proxyUrlFromPacResult("")).toBeNull();
+  });
+});
+
+describe("unsetProxyVars", () => {
+  it("selects both variables on a clean environment", () => {
+    expect(unsetProxyVars({}).map((v) => v.name)).toEqual(["HTTP_PROXY", "HTTPS_PROXY"]);
+  });
+
+  it("skips a variable already present in either spelling (never overridden)", () => {
+    expect(unsetProxyVars({ HTTP_PROXY: "http://a:1" }).map((v) => v.name)).toEqual([
+      "HTTPS_PROXY",
+    ]);
+    expect(unsetProxyVars({ https_proxy: "http://a:1" }).map((v) => v.name)).toEqual([
+      "HTTP_PROXY",
+    ]);
+    expect(unsetProxyVars({ HTTP_PROXY: "http://a:1", https_proxy: "http://a:1" })).toEqual([]);
+  });
+});
diff --git a/packages/docs/content/interfaces.en.md b/packages/docs/content/interfaces.en.md
index 8646723..d3b6691 100644
--- a/packages/docs/content/interfaces.en.md
+++ b/packages/docs/content/interfaces.en.md
@@ -127,6 +127,7 @@ interface EnvironmentConfig {
   sessionScratchpadDir?: string;            // this Session's scratchpad (scratchpad/<sessionId>); enables truncated-output recovery
   services?: EnvironmentServices;           // runtime services injected into individual tools
   vault?: Record<string, string>;           // Vault env vars, injected into exec_command / input_command subprocesses
+  stripProxyEnv?: () => boolean;            // true = strip HTTP(S)_PROXY/ALL_PROXY (NO_PROXY kept) from command subprocesses; re-read per spawn, absent = proxy allowed
 }
 
 interface EnvironmentServices {
diff --git a/packages/docs/content/interfaces.zh.md b/packages/docs/content/interfaces.zh.md
index 69cd953..0cdd614 100644
--- a/packages/docs/content/interfaces.zh.md
+++ b/packages/docs/content/interfaces.zh.md
@@ -127,6 +127,7 @@ interface EnvironmentConfig {
   sessionScratchpadDir?: string;            // 本 Session 的 scratchpad（scratchpad/<sessionId>），提供后启用截断输出恢复
   services?: EnvironmentServices;           // 注入给个别工具的运行时服务
   vault?: Record<string, string>;           // Vault 环境变量,注入 exec_command / input_command 子进程
+  stripProxyEnv?: () => boolean;            // 返回 true 时从命令子进程剥除 HTTP(S)_PROXY/ALL_PROXY（保留 NO_PROXY）；每次 spawn 重读，缺省即允许代理
 }
 
 interface EnvironmentServices {
diff --git a/packages/docs/content/server-api.en.md b/packages/docs/content/server-api.en.md
index 850842f..70573a1 100644
--- a/packages/docs/content/server-api.en.md
+++ b/packages/docs/content/server-api.en.md
@@ -67,6 +67,15 @@ curl -c cookies.txt -H "Content-Type: application/json" \
 | POST | /api/admin/users/:userId/password | Reset a password (invalidates all of that user's login sessions) |
 | DELETE | /api/admin/users/:userId | Delete a user |
 
+### Server Settings (admin only)
+
+| Method | Path | Description |
+| --- | --- | --- |
+| GET | /api/admin/settings | Server-global settings: `{settings: {useSystemProxy}}` |
+| PUT | /api/admin/settings | Update settings (fields optional; omitted fields keep their current value), returns the full updated settings |
+
+`useSystemProxy` is the "use system HTTP proxy" switch (default on): while on, the server and its child processes honor HTTP_PROXY / HTTPS_PROXY / NO_PROXY (both spellings) for outbound traffic; while off, the server always connects directly and the proxy variables are stripped from agent command subprocess environments (NO_PROXY is kept). In either state the effective NO_PROXY always includes `localhost,127.0.0.1,::1` (loopback is never proxied). Toggling takes effect for newly initiated connections immediately — no restart.
+
 ### Version and Self-Update
 
 | Method | Path | Description |
diff --git a/packages/docs/content/server-api.zh.md b/packages/docs/content/server-api.zh.md
index 3cd94e1..f96b7aa 100644
--- a/packages/docs/content/server-api.zh.md
+++ b/packages/docs/content/server-api.zh.md
@@ -67,6 +67,15 @@ curl -c cookies.txt -H "Content-Type: application/json" \
 | POST | /api/admin/users/:userId/password | 重置密码（该用户全部登录会话失效） |
 | DELETE | /api/admin/users/:userId | 删除用户 |
 
+### 服务端设置（仅管理员）
+
+| 方法 | 路径 | 说明 |
+| --- | --- | --- |
+| GET | /api/admin/settings | 服务端全局设置：`{settings: {useSystemProxy}}` |
+| PUT | /api/admin/settings | 更新设置（字段可省略，省略即保持现值），返回更新后的完整设置 |
+
+`useSystemProxy` 即「使用系统 HTTP 代理」开关（默认开）：开时服务端及其子进程出网遵循 HTTP_PROXY / HTTPS_PROXY / NO_PROXY（大小写并存）；关时服务端一律直连，并从 Agent 命令子进程环境中剥除代理变量（NO_PROXY 保留）。任一状态下生效的 NO_PROXY 恒包含 `localhost,127.0.0.1,::1`（回环不代理）。切换即时生效（对新发起的连接），无需重启。
+
 ### 版本与在线更新
 
 | 方法 | 路径 | 说明 |
diff --git a/packages/server/package.json b/packages/server/package.json
index 3caf1d3..63c9fe9 100644
--- a/packages/server/package.json
+++ b/packages/server/package.json
@@ -44,6 +44,7 @@
     "hono": "^4.12.34",
     "smol-toml": "^1.3.0",
     "tar": "^7.5.21",
+    "undici": "^7.29.0",
     "yaml": "^2.5.0"
   },
   "devDependencies": {
diff --git a/packages/server/src/api/types.ts b/packages/server/src/api/types.ts
index fc28d64..d7b4551 100644
--- a/packages/server/src/api/types.ts
+++ b/packages/server/src/api/types.ts
@@ -119,6 +119,28 @@ export interface AdminPasswordResetRequest {
   password: string;
 }
 
+/** Admin-level server-global settings (SQLite server_settings; design § "出网与系统代理"). */
+export interface ServerSettings {
+  /**
+   * "Use system HTTP proxy" (default on): whether the server process and its child
+   * processes reach the internet through the proxy named by HTTP_PROXY / HTTPS_PROXY
+   * (both spellings). Off = direct connections, with the proxy variables also stripped
+   * from agent command subprocess environments. Either way the effective NO_PROXY always
+   * includes localhost/127.0.0.1/::1 (loopback is never proxied). Toggling applies to
+   * newly initiated connections immediately — no restart.
+   */
+  useSystemProxy: boolean;
+}
+
+export interface ServerSettingsResponse {
+  settings: ServerSettings;
+}
+
+/** PUT body: every field optional, omitted fields keep their current value (mirrors prefs). */
+export interface ServerSettingsUpdateRequest {
+  useSystemProxy?: boolean;
+}
+
 /** User UI preferences (SQLite ui_prefs, free-form JSON; known keys declared here). */
 export interface UiPrefs {
   theme?: "light" | "dark";
diff --git a/packages/server/src/app.ts b/packages/server/src/app.ts
index 54de097..bcbffef 100644
--- a/packages/server/src/app.ts
+++ b/packages/server/src/app.ts
@@ -22,6 +22,7 @@ import { MembersRepo } from "./db/repos/members.js";
 import { ProjectsRepo } from "./db/repos/projects.js";
 import { GoalsRepo } from "./db/repos/goals.js";
 import { SchedulesRepo } from "./db/repos/schedules.js";
+import { ServerSettingsRepo } from "./db/repos/server-settings.js";
 import { SessionsRepo } from "./db/repos/sessions.js";
 import { TraceIndexRepo } from "./db/repos/trace-index.js";
 import { UiPrefsRepo } from "./db/repos/ui-prefs.js";
@@ -33,6 +34,7 @@ import type { AppEnv } from "./auth/middleware.js";
 import { AuthService } from "./auth/service.js";
 import { handleError, HttpError, errorBody } from "./http/errors.js";
 import { adminUsersRoutes } from "./http/routes/admin.js";
+import { adminSettingsRoutes } from "./http/routes/admin-settings.js";
 import { authRoutes } from "./http/routes/auth.js";
 import { meRoutes } from "./http/routes/me.js";
 import { eventsRoutes, userChannelKey } from "./http/routes/events.js";
@@ -93,6 +95,8 @@ export interface AppDeps {
   db: DatabaseSync;
   sessionsRepo: SessionsRepo;
   prefsRepo: UiPrefsRepo;
+  /** Admin-level server-global settings (currently the "use system HTTP proxy" switch). */
+  serverSettingsRepo: ServerSettingsRepo;
   authService: AuthService;
   adminService: AdminService;
   projectService: ProjectService;
@@ -152,6 +156,13 @@ export function buildAppDeps(config: ServerConfig, overrides: BuildDepsOverrides
   const usageRepo = new UsageRepo(db);
   const errorsRepo = new ErrorsRepo(db);
   const prefsRepo = new UiPrefsRepo(db);
+  const serverSettingsRepo = new ServerSettingsRepo(db);
+  // Proxy-off also strips HTTP(S)_PROXY/ALL_PROXY from agent command subprocess
+  // environments (design § "出网与系统代理"). A getter, not a snapshot: it is re-read at
+  // every command spawn, so a toggle reaches already-loaded Sessions. Threaded through
+  // BOTH core entry paths — the loader (resume/self-heal) and SessionService (creation,
+  // whose runtime the manager adopts for the first Task).
+  const stripProxyEnv = () => !serverSettingsRepo.getUseSystemProxy();
   const schedulesRepo = new SchedulesRepo(db);
   const goalsRepo = new GoalsRepo(db);
 
@@ -203,7 +214,8 @@ export function buildAppDeps(config: ServerConfig, overrides: BuildDepsOverrides
   const manager = new SessionManager({
     sessions: sessionsRepo,
     channels,
-    loader: overrides.loader ?? createCoreSessionLoader(config.root, sessionSources),
+    loader:
+      overrides.loader ?? createCoreSessionLoader(config.root, sessionSources, { stripProxyEnv }),
     sources: sessionSources,
     recorder,
     errors,
@@ -252,6 +264,7 @@ export function buildAppDeps(config: ServerConfig, overrides: BuildDepsOverrides
     projectConfig: projectConfigService,
     sources: sessionSources,
     traceIndex,
+    stripProxyEnv,
   });
   // Schedule scheduler: active only while the server is running. Only
   // assembled here; start() is called in index.ts (tests drive it via tickOnce, no real timer).
@@ -275,6 +288,7 @@ export function buildAppDeps(config: ServerConfig, overrides: BuildDepsOverrides
     db,
     sessionsRepo,
     prefsRepo,
+    serverSettingsRepo,
     authService,
     adminService,
     projectService,
@@ -390,6 +404,7 @@ export function createApp(deps: AppDeps): Hono<AppEnv> {
   app.route("/api/me", meRoutes(deps));
   app.route("/api/version", versionRoutes(deps));
   app.route("/api/admin/users", adminUsersRoutes(deps));
+  app.route("/api/admin/settings", adminSettingsRoutes(deps));
   app.route("/api/events", eventsRoutes(deps));
   // Skill library listing: readable once logged in, not nested under a Project prefix.
   app.route("/api/skills", skillLibraryRoutes());
diff --git a/packages/server/src/db/repos/server-settings.ts b/packages/server/src/db/repos/server-settings.ts
new file mode 100644
index 0000000..4f13f91
--- /dev/null
+++ b/packages/server/src/db/repos/server-settings.ts
@@ -0,0 +1,37 @@
+/**
+ * server_settings table repo (admin-level server-global settings): key-value storage
+ * with JSON-encoded values. An absent row means the setting's built-in default, so
+ * settings added after a web.db was formed need no migration.
+ */
+import type { DatabaseSync } from "node:sqlite";
+
+/** Key of the "use system HTTP proxy" switch (design § "出网与系统代理"); default on. */
+const USE_SYSTEM_PROXY_KEY = "use_system_proxy";
+
+export class ServerSettingsRepo {
+  constructor(private readonly db: DatabaseSync) {}
+
+  /** Returns the raw JSON-encoded value; null if never set. */
+  get(key: string): string | null {
+    const r = this.db.prepare("SELECT value FROM server_settings WHERE key = ?").get(key);
+    return r ? (r.value as string) : null;
+  }
+
+  set(key: string, value: string): void {
+    this.db
+      .prepare(
+        `INSERT INTO server_settings (key, value) VALUES (?, ?)
+         ON CONFLICT(key) DO UPDATE SET value = excluded.value`,
+      )
+      .run(key, value);
+  }
+
+  /** The "use system HTTP proxy" switch; an absent (or unreadable) row reads as the default: on. */
+  getUseSystemProxy(): boolean {
+    return this.get(USE_SYSTEM_PROXY_KEY) !== "false";
+  }
+
+  setUseSystemProxy(value: boolean): void {
+    this.set(USE_SYSTEM_PROXY_KEY, JSON.stringify(value));
+  }
+}
diff --git a/packages/server/src/db/schema.ts b/packages/server/src/db/schema.ts
index a1f5412..a1a0de7 100644
--- a/packages/server/src/db/schema.ts
+++ b/packages/server/src/db/schema.ts
@@ -121,6 +121,10 @@ CREATE TABLE IF NOT EXISTS ui_prefs (
   user_id    TEXT PRIMARY KEY REFERENCES users(user_id) ON DELETE CASCADE,
   prefs_json TEXT NOT NULL                    -- {theme?, lastProjectId?, ...} free-form JSON
 );
+CREATE TABLE IF NOT EXISTS server_settings (   -- admin-level server-global settings (GET/PUT /api/admin/settings)
+  key   TEXT PRIMARY KEY,                     -- setting name, e.g. 'use_system_proxy'
+  value TEXT NOT NULL                         -- JSON-encoded value; an absent row means the setting's built-in default
+);
 CREATE TABLE IF NOT EXISTS trace_files (       -- DERIVED CACHE of the on-disk Trace tree (services/trace-index.ts): the directories stay the single source of truth, every row is rebuildable from disk, and a row is never authority for absence — consumers reconcile + retry on a miss, so a stale index costs one extra scan, never a false 404
   project_id TEXT NOT NULL,
   agent_id   TEXT NOT NULL,
diff --git a/packages/server/src/http/routes/admin-settings.ts b/packages/server/src/http/routes/admin-settings.ts
new file mode 100644
index 0000000..4e6f602
--- /dev/null
+++ b/packages/server/src/http/routes/admin-settings.ts
@@ -0,0 +1,44 @@
+/**
+ * Admin server-settings routes (admin only, 403 for non-admins):
+ * GET|PUT /api/admin/settings — the server-global settings stored in server_settings
+ * (currently the "use system HTTP proxy" switch, design § "出网与系统代理").
+ * A PUT applies immediately: the persisted value is written first, then the process
+ * dispatcher is rebuilt so new outbound connections follow the toggle without a restart.
+ */
+import { Hono } from "hono";
+import type { ServerSettingsResponse } from "../../api/types.js";
+import { HttpError } from "../errors.js";
+import type { AppEnv } from "../../auth/middleware.js";
+import { optionalBoolean, readJson } from "../validate.js";
+import type { AppDeps } from "../../app.js";
+import { setUseSystemProxy } from "../../net/proxy.js";
+
+export function adminSettingsRoutes(deps: AppDeps): Hono<AppEnv> {
+  const app = new Hono<AppEnv>();
+
+  app.use("*", async (c, next) => {
+    if (!c.var.user.isAdmin) {
+      throw new HttpError(403, "admin_required", "Only an admin can perform this operation.");
+    }
+    await next();
+  });
+
+  const settings = (): ServerSettingsResponse => ({
+    settings: { useSystemProxy: deps.serverSettingsRepo.getUseSystemProxy() },
+  });
+
+  app.get("/", (c) => c.json(settings()));
+
+  app.put("/", async (c) => {
+    const body = await readJson(c);
+    const useSystemProxy = optionalBoolean(body, "useSystemProxy");
+    if (useSystemProxy !== undefined) {
+      deps.serverSettingsRepo.setUseSystemProxy(useSystemProxy);
+      // Mirror into the process: rebuilds the global fetch dispatcher (live toggle).
+      setUseSystemProxy(useSystemProxy);
+    }
+    return c.json(settings());
+  });
+
+  return app;
+}
diff --git a/packages/server/src/index.ts b/packages/server/src/index.ts
index db877d6..28abc63 100644
--- a/packages/server/src/index.ts
+++ b/packages/server/src/index.ts
@@ -15,11 +15,19 @@ import { config as loadDotenv } from "dotenv";
 import { serve } from "@hono/node-server";
 import { buildAppDeps, createApp } from "./app.js";
 import { resolveServerConfig } from "./config.js";
+import { installGlobalProxyDispatcher, setUseSystemProxy } from "./net/proxy.js";
 import { loopbackHostRoles } from "./services/preview-token.js";
 import { acquireServerLock, liveServerLock, releaseServerLock } from "./lock.js";
 
 loadDotenv({ quiet: true });
 
+// Outbound proxy support, installed at the earliest point (right after dotenv, which may
+// itself define HTTP_PROXY): replaces globalThis.fetch with undici's and sets the global
+// dispatcher, starting from the switch default (on). The persisted value can only be
+// read once the database is open, so it is applied via setUseSystemProxy right after
+// buildAppDeps below — nothing in between makes an outbound request. See net/proxy.ts.
+installGlobalProxyDispatcher();
+
 /** Exit code for "another server already owns this data root" (see lock.ts). */
 const EXIT_ALREADY_RUNNING = 3;
 
@@ -39,6 +47,10 @@ if (existingLock) {
 }
 
 const deps = buildAppDeps(config);
+// The database is open now: bring the dispatcher in line with the persisted
+// "use system HTTP proxy" switch (an absent row reads as the default: on) before the
+// first possible outbound request (update check, LLM calls — all behind HTTP handlers).
+setUseSystemProxy(deps.serverSettingsRepo.getUseSystemProxy());
 const app = createApp(deps);
 
 // Built-in admin seed (idempotent): creates admin and adopts default_project when the
diff --git a/packages/server/src/net/proxy.ts b/packages/server/src/net/proxy.ts
new file mode 100644
index 0000000..689a7ac
--- /dev/null
+++ b/packages/server/src/net/proxy.ts
@@ -0,0 +1,96 @@
+/**
+ * Outbound networking and the "use system HTTP proxy" switch (design § "出网与系统代理").
+ *
+ * Node 24's built-in fetch does not read the proxy environment variables
+ * (NODE_USE_ENV_PROXY is ineffective on 24.18), so the server routes ALL of its own
+ * outbound traffic through undici: the startup entry replaces `globalThis.fetch` with
+ * undici's fetch once, and this module keeps undici's global dispatcher in line with the
+ * admin-level setting — undici's fetch resolves the global dispatcher per call, so a
+ * toggle takes effect for newly initiated connections without a restart.
+ *
+ * Dispatcher per setting:
+ *   - on (default): `EnvHttpProxyAgent` — honors HTTP_PROXY / HTTPS_PROXY (both
+ *     spellings; undici reads the lowercase name first) with a NO_PROXY list merged from
+ *     the environment plus the loopback names;
+ *   - off: a plain `Agent` — direct connections, proxy variables ignored.
+ *
+ * The loopback merge is load-bearing in either state: the CLI's readiness probe
+ * (`penguin web` imports the server in-process and polls its own root path), SSE, and
+ * Workspace previews all ride the loopback names, so a proxy that intercepts loopback
+ * would take the whole App down. `localhost,127.0.0.1,::1` is therefore ALWAYS appended
+ * to the effective NO_PROXY, regardless of what the environment declares.
+ *
+ * The value persisted in server_settings stays authoritative (the routes read/write the
+ * repo); this module only mirrors it into the process-global dispatcher. Stripping the
+ * proxy variables from agent command subprocesses when the switch is off lives in core
+ * (CommandSessionManager, threaded through the session loader), not here.
+ */
+import { Agent, EnvHttpProxyAgent, fetch as undiciFetch, setGlobalDispatcher } from "undici";
+import type { Dispatcher } from "undici";
+
+/** Loopback names every effective NO_PROXY must contain (see module doc). */
+export const LOOPBACK_NO_PROXY = ["localhost", "127.0.0.1", "::1"] as const;
+
+/**
+ * The effective NO_PROXY: the environment's entries (lowercase spelling first, matching
+ * undici's own precedence) with the loopback names appended when missing. Exported as a
+ * pure helper for tests; `env` defaults to the real process environment.
+ */
+export function mergedNoProxy(env: NodeJS.ProcessEnv = process.env): string {
+  const raw = env.no_proxy ?? env.NO_PROXY ?? "";
+  // Same separators undici's parser accepts (comma or whitespace).
+  const entries = raw.split(/[,\s]/).filter((e) => e !== "");
+  const present = new Set(entries.map((e) => e.toLowerCase()));
+  for (const name of LOOPBACK_NO_PROXY) {
+    if (!present.has(name)) entries.push(name);
+  }
+  return entries.join(",");
+}
+
+/**
+ * Builds the global dispatcher for a switch state (pure choice, exported for tests):
+ * on → EnvHttpProxyAgent with the merged NO_PROXY, off → direct-connect Agent.
+ */
+export function buildProxyDispatcher(useSystemProxy: boolean, env?: NodeJS.ProcessEnv): Dispatcher {
+  // The merged list is passed via opts.noProxy, which REPLACES the environment lookup
+  // inside EnvHttpProxyAgent — merging is this module's job (undici would otherwise use
+  // env NO_PROXY verbatim, without the loopback exemption).
+  return useSystemProxy ? new EnvHttpProxyAgent({ noProxy: mergedNoProxy(env) }) : new Agent();
+}
+
+/** Current switch state mirrored for the dispatcher (the DB row is the persisted truth). */
+let useSystemProxy = true;
+/** True once the startup entry has installed undici globally (never in tests). */
+let installed = false;
+
+/**
+ * One-time install at the startup entry (index.ts), before anything can fetch: replaces
+ * `globalThis.fetch` with undici's and sets the initial dispatcher. Starts from the
+ * default (on) — the entry applies the persisted value via {@link setUseSystemProxy} as
+ * soon as the database is open, before any outbound request exists. Tests never call
+ * this, so they keep the runtime's own fetch (and their fetch stubs).
+ */
+export function installGlobalProxyDispatcher(): void {
+  installed = true;
+  setGlobalDispatcher(buildProxyDispatcher(useSystemProxy));
+  // Cast: undici's fetch is typed against its own RequestInit/Response declarations,
+  // which are structurally compatible with the runtime globals for every caller here.
+  globalThis.fetch = undiciFetch as unknown as typeof globalThis.fetch;
+}
+
+/**
+ * Applies a switch state to the process: rebuilds the global dispatcher so new
+ * connections follow it immediately (no restart). Called by the startup entry with the
+ * persisted value and by PUT /api/admin/settings on every toggle. Outside the installed
+ * runtime (tests) it only records the state.
+ */
+export function setUseSystemProxy(value: boolean): void {
+  if (value === useSystemProxy) return;
+  useSystemProxy = value;
+  if (installed) setGlobalDispatcher(buildProxyDispatcher(useSystemProxy));
+}
+
+/** The switch state the dispatcher currently reflects. */
+export function getUseSystemProxy(): boolean {
+  return useSystemProxy;
+}
diff --git a/packages/server/src/runtime/session-manager.ts b/packages/server/src/runtime/session-manager.ts
index 4ff9361..f3352ba 100644
--- a/packages/server/src/runtime/session-manager.ts
+++ b/packages/server/src/runtime/session-manager.ts
@@ -121,14 +121,21 @@ export interface SessionLoader {
  * lets the no-Trace self-heal rebuild re-record a known origin into the fresh session_meta;
  * with no registry entry (e.g. the process restarted and no Trace was ever written) the
  * rebuilt Session is unsourced — session_meta is the single source of truth, and none survived.
+ * `opts.stripProxyEnv` threads the "use system HTTP proxy" switch into core (a live getter:
+ * true = strip HTTP(S)_PROXY/ALL_PROXY from agent command subprocess environments).
  */
-export function createCoreSessionLoader(root: string, sources?: SessionSources): SessionLoader {
+export function createCoreSessionLoader(
+  root: string,
+  sources?: SessionSources,
+  opts: { stripProxyEnv?: () => boolean } = {},
+): SessionLoader {
   return {
     async load(row: SessionRow): Promise<RuntimeSession> {
       const agent = await createAgent({
         root,
         projectId: row.projectId,
         agentId: row.agentId,
+        ...(opts.stripProxyEnv ? { stripProxyEnv: opts.stripProxyEnv } : {}),
       });
       const located = await findLatestTraceFile(
         tracesDir(root, row.projectId, row.agentId),
diff --git a/packages/server/src/services/session-service.ts b/packages/server/src/services/session-service.ts
index a3b029b..a0baff9 100644
--- a/packages/server/src/services/session-service.ts
+++ b/packages/server/src/services/session-service.ts
@@ -51,6 +51,12 @@ export interface SessionServiceDeps {
   sources: SessionSources;
   /** Trace-file index: discovery / adoption / stats serve from it (mtime-gated reconciler; no per-request walks). */
   traceIndex: TraceIndexService;
+  /**
+   * "Use system HTTP proxy" switch threading (same getter the session loader passes,
+   * see createCoreSessionLoader): the runtime created here is adopted by the manager
+   * and runs the Session's first Task, so it needs the strip policy too.
+   */
+  stripProxyEnv?: () => boolean;
 }
 
 export class SessionService {
@@ -319,6 +325,7 @@ export class SessionService {
       root: this.deps.root,
       projectId: args.projectId,
       agentId: args.agentId,
+      ...(this.deps.stripProxyEnv ? { stripProxyEnv: this.deps.stripProxyEnv } : {}),
     });
     let session;
     try {
diff --git a/packages/server/test/admin-settings.test.ts b/packages/server/test/admin-settings.test.ts
new file mode 100644
index 0000000..a26da88
--- /dev/null
+++ b/packages/server/test/admin-settings.test.ts
@@ -0,0 +1,68 @@
+/**
+ * Admin server-settings route tests: permission boundary (non-admin 403), the
+ * "use system HTTP proxy" default (absent row reads as on), PUT persistence and
+ * validation, and merge semantics (an omitted field keeps its current value).
+ */
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import type { ServerSettingsResponse } from "../src/api/types.js";
+import { apiClient, createTestApp, loginAdmin, provisionUser } from "./helpers.js";
+import type { TestApp } from "./helpers.js";
+
+describe("admin server settings", () => {
+  let t: TestApp;
+  let admin: ReturnType<typeof apiClient>;
+
+  beforeEach(async () => {
+    t = await createTestApp();
+    admin = apiClient(t.app, (await loginAdmin(t.app)).cookie);
+  });
+  afterEach(async () => {
+    await t.cleanup();
+  });
+
+  const getSettings = async (api: ReturnType<typeof apiClient> = admin) => {
+    const res = await api.get("/api/admin/settings");
+    expect(res.status).toBe(200);
+    return (await res.json()) as ServerSettingsResponse;
+  };
+
+  it("non-admin access is always 403", async () => {
+    const { cookie } = await provisionUser(t.app, "norm");
+    const api = apiClient(t.app, cookie);
+    expect((await api.get("/api/admin/settings")).status).toBe(403);
+    expect((await api.put("/api/admin/settings", { useSystemProxy: false })).status).toBe(403);
+    // The failed PUT changed nothing.
+    expect((await getSettings()).settings.useSystemProxy).toBe(true);
+  });
+
+  it("useSystemProxy defaults to on while no row exists", async () => {
+    expect(t.deps.db.prepare("SELECT COUNT(*) AS n FROM server_settings").get()).toMatchObject({
+      n: 0,
+    });
+    expect((await getSettings()).settings.useSystemProxy).toBe(true);
+  });
+
+  it("PUT persists the toggle and echoes the full settings", async () => {
+    const off = await admin.put("/api/admin/settings", { useSystemProxy: false });
+    expect(off.status).toBe(200);
+    expect(((await off.json()) as ServerSettingsResponse).settings.useSystemProxy).toBe(false);
+    // Round-trips through the repo (the DB row, not process state, is what GET serves).
+    expect((await getSettings()).settings.useSystemProxy).toBe(false);
+    expect(t.deps.serverSettingsRepo.getUseSystemProxy()).toBe(false);
+
+    const on = await admin.put("/api/admin/settings", { useSystemProxy: true });
+    expect(on.status).toBe(200);
+    expect((await getSettings()).settings.useSystemProxy).toBe(true);
+  });
+
+  it("an omitted field keeps its current value; a non-boolean is 400", async () => {
+    await admin.put("/api/admin/settings", { useSystemProxy: false });
+    // Empty PUT: no-op, still returns the current settings.
+    const noop = await admin.put("/api/admin/settings", {});
+    expect(noop.status).toBe(200);
+    expect(((await noop.json()) as ServerSettingsResponse).settings.useSystemProxy).toBe(false);
+    // Type check: only booleans are accepted, and a rejected write changes nothing.
+    expect((await admin.put("/api/admin/settings", { useSystemProxy: "on" })).status).toBe(400);
+    expect((await getSettings()).settings.useSystemProxy).toBe(false);
+  });
+});
diff --git a/packages/server/test/proxy.test.ts b/packages/server/test/proxy.test.ts
new file mode 100644
index 0000000..5396099
--- /dev/null
+++ b/packages/server/test/proxy.test.ts
@@ -0,0 +1,51 @@
+/**
+ * Unit tests for the outbound-proxy module's pure parts: the NO_PROXY loopback merge
+ * and the dispatcher choice per switch state. No real network and no global install —
+ * installGlobalProxyDispatcher (fetch replacement) runs only in the production entry.
+ */
+import { describe, expect, it } from "vitest";
+import { Agent, EnvHttpProxyAgent } from "undici";
+import { buildProxyDispatcher, mergedNoProxy } from "../src/net/proxy.js";
+
+describe("mergedNoProxy", () => {
+  it("yields exactly the loopback names when the environment has no NO_PROXY", () => {
+    expect(mergedNoProxy({})).toBe("localhost,127.0.0.1,::1");
+  });
+
+  it("appends the loopback names after the environment's entries", () => {
+    expect(mergedNoProxy({ NO_PROXY: "example.com,.corp.internal" })).toBe(
+      "example.com,.corp.internal,localhost,127.0.0.1,::1",
+    );
+  });
+
+  it("prefers the lowercase spelling, like undici itself", () => {
+    expect(mergedNoProxy({ no_proxy: "a.example", NO_PROXY: "b.example" })).toBe(
+      "a.example,localhost,127.0.0.1,::1",
+    );
+  });
+
+  it("does not duplicate loopback names already present (case-insensitively)", () => {
+    expect(mergedNoProxy({ NO_PROXY: "LOCALHOST,::1" })).toBe("LOCALHOST,::1,127.0.0.1");
+  });
+
+  it("survives messy separators (comma/whitespace mix, empty segments)", () => {
+    expect(mergedNoProxy({ NO_PROXY: " example.com ,, other.example " })).toBe(
+      "example.com,other.example,localhost,127.0.0.1,::1",
+    );
+  });
+});
+
+describe("buildProxyDispatcher", () => {
+  it("on → EnvHttpProxyAgent (proxy env honored), off → plain Agent (direct)", async () => {
+    const on = buildProxyDispatcher(true, {});
+    const off = buildProxyDispatcher(false, {});
+    try {
+      expect(on).toBeInstanceOf(EnvHttpProxyAgent);
+      expect(off).toBeInstanceOf(Agent);
+      expect(off).not.toBeInstanceOf(EnvHttpProxyAgent);
+    } finally {
+      await on.close();
+      await off.close();
+    }
+  });
+});
diff --git a/packages/web/src/api/endpoints.ts b/packages/web/src/api/endpoints.ts
index 19fdb27..ee75f6d 100644
--- a/packages/web/src/api/endpoints.ts
+++ b/packages/web/src/api/endpoints.ts
@@ -50,6 +50,8 @@ import type {
   ScheduleItem,
   SchedulesResponse,
   ScheduleUpsertRequest,
+  ServerSettingsResponse,
+  ServerSettingsUpdateRequest,
   SessionCategory,
   SessionCreateRequest,
   SessionCreateResponse,
@@ -114,6 +116,13 @@ export const adminResetPassword = (userId: string, body: AdminPasswordResetReque
 export const adminDeleteUser = (userId: string) =>
   apiFetch<void>(`/api/admin/users/${encodeURIComponent(userId)}`, { method: "DELETE" });
 
+/** Server-global settings (admin only): currently the "use system HTTP proxy" switch. */
+export const adminGetSettings = () => apiFetch<ServerSettingsResponse>("/api/admin/settings");
+
+/** Omitted fields keep their current value; applies immediately (no restart). */
+export const adminPutSettings = (body: ServerSettingsUpdateRequest) =>
+  apiFetch<ServerSettingsResponse>("/api/admin/settings", { method: "PUT", body });
+
 // Project & members --------------------------------------------------------------
 
 export const listProjects = () => apiFetch<ProjectsResponse>("/api/projects");
diff --git a/packages/web/src/components/layout/sidebar.tsx b/packages/web/src/components/layout/sidebar.tsx
index e91dec1..557e2cc 100644
--- a/packages/web/src/components/layout/sidebar.tsx
+++ b/packages/web/src/components/layout/sidebar.tsx
@@ -234,6 +234,35 @@ export function Sidebar({
       setUpdateChecking(false);
     }
   };
+  /**
+   * Admin-only "use system HTTP proxy" switch (server-global, design § "出网与系统代理"):
+   * null = not hydrated yet. Fetched lazily the first time an ADMIN opens the dropdown —
+   * same laziness as the version info above, and non-admins never call the endpoint (the
+   * row is not rendered for them either). A failed hydration stays null (row disabled)
+   * and is retried on the next open.
+   */
+  const [useSystemProxy, setUseSystemProxyState] = useState<boolean | null>(null);
+  useEffect(() => {
+    if (!userOpen || user?.isAdmin !== true || useSystemProxy !== null) return;
+    let cancelled = false;
+    void api
+      .adminGetSettings()
+      .then((res) => {
+        if (!cancelled) setUseSystemProxyState(res.settings.useSystemProxy);
+      })
+      .catch(() => undefined);
+    return () => {
+      cancelled = true;
+    };
+  }, [userOpen, user?.isAdmin, useSystemProxy]);
+  /** Saved immediately on toggle (the user-menu quick-control convention): optimistic flip, reverted with a toast on failure. */
+  const setUseSystemProxy = (value: boolean) => {
+    setUseSystemProxyState(value);
+    void api.adminPutSettings({ useSystemProxy: value }).catch((e: unknown) => {
+      setUseSystemProxyState(!value);
+      toastError(apiErrorText(e));
+    });
+  };
   const currentProjectId = currentProject?.projectId ?? null;
   const collapseStoreKey = currentProjectId === null ? null : collapsedGroupsKey(currentProjectId);
   const pinStoreKey = currentProjectId === null ? null : pinnedGroupsKey(currentProjectId);
@@ -1005,6 +1034,19 @@ export function Sidebar({
             <SettingRow label={S.settings.showCliSessions}>
               <Switch checked={showCliSessions} onChange={setShowCliSessions} />
             </SettingRow>
+            {/* Admin-only, server-global (all users), saved immediately on toggle; the
+                tooltip spells out the scope and the loopback exemption. Disabled (showing
+                the default: on) until the stored value has hydrated, so a click can never
+                write a value the admin was not looking at. */}
+            {user?.isAdmin && (
+              <SettingRow label={S.settings.useSystemProxy} title={S.settings.useSystemProxyHint}>
+                <Switch
+                  checked={useSystemProxy ?? true}
+                  onChange={setUseSystemProxy}
+                  disabled={useSystemProxy === null}
+                />
+              </SettingRow>
+            )}
           </div>
           <div className="mt-1 border-t border-gray-100 pt-1 dark:border-gray-800">
             <button
@@ -1332,9 +1374,18 @@ function SessionRow({
   );
 }
 
-function SettingRow({ label, children }: { label: string; children: ReactNode }) {
+function SettingRow({
+  label,
+  title,
+  children,
+}: {
+  label: string;
+  /** Optional row tooltip (e.g. the system-proxy row's scope + loopback-exemption hint). */
+  title?: string;
+  children: ReactNode;
+}) {
   return (
-    <div>
+    <div {...(title !== undefined ? { title } : {})}>
       <p className="mb-1 text-[11px] font-medium text-gray-500 dark:text-gray-400">{label}</p>
       {children}
     </div>
diff --git a/packages/web/src/lib/strings-en.ts b/packages/web/src/lib/strings-en.ts
index 2198c7f..82ea40f 100644
--- a/packages/web/src/lib/strings-en.ts
+++ b/packages/web/src/lib/strings-en.ts
@@ -33,6 +33,11 @@ export const en: Strings = {
     language: "Language",
     /** Sidebar Session list: also show CLI-created Sessions (default off — the list then never scans the Trace directories). */
     showCliSessions: "Show CLI sessions",
+    /** Admin-only server-global switch (design § "出网与系统代理"): saved immediately on toggle. */
+    useSystemProxy: "Use system HTTP proxy",
+    /** Row tooltip: scope (server + its child processes, server-wide) and the loopback exemption. */
+    useSystemProxyHint:
+      "Whether the server and its child processes (update checks, LLM requests, agent commands) reach the internet through the proxy named by HTTP_PROXY / HTTPS_PROXY. Applies server-wide; loopback addresses (localhost, 127.0.0.1, ::1) always connect directly. When off, the server connects directly and the proxy variables are removed from agent command subprocess environments.",
     theme: "Theme",
     themeLight: "Light",
     themeDark: "Dark",
diff --git a/packages/web/src/lib/strings.ts b/packages/web/src/lib/strings.ts
index f2b2476..88c9f3c 100644
--- a/packages/web/src/lib/strings.ts
+++ b/packages/web/src/lib/strings.ts
@@ -35,6 +35,11 @@ export const zh = {
     language: "语言",
     /** Sidebar Session list: also show CLI-created Sessions (default off — the list then never scans the Trace directories). */
     showCliSessions: "显示 CLI 会话",
+    /** Admin-only server-global switch (design § "出网与系统代理"): saved immediately on toggle. */
+    useSystemProxy: "使用系统 HTTP 代理",
+    /** Row tooltip: scope (server + its child processes, server-wide) and the loopback exemption. */
+    useSystemProxyHint:
+      "服务端及其子进程（更新检查、LLM 请求、Agent 命令）出网时是否使用 HTTP_PROXY / HTTPS_PROXY 环境变量指定的代理，对整个服务端全局生效；回环地址（localhost、127.0.0.1、::1）始终直连。关闭后服务端一律直连，并从 Agent 命令子进程环境中移除代理变量。",
     theme: "主题",
     themeLight: "浅色",
     themeDark: "深色",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index a04e782..4257413 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -264,6 +264,9 @@ importers:
       tar:
         specifier: ^7.5.21
         version: 7.5.22
+      undici:
+        specifier: ^7.29.0
+        version: 7.29.0
       yaml:
         specifier: ^2.5.0
         version: 2.9.0
@@ -7279,8 +7282,7 @@ snapshots:
 
   undici@6.28.0: {}
 
-  undici@7.29.0:
-    optional: true
+  undici@7.29.0: {}
 
   unified@11.0.5:
     dependencies: