diff --git a/crates/agent-gui/src-tauri/src/commands/app/update.rs b/crates/agent-gui/src-tauri/src/commands/app/update.rs
index e9ca758a7..8c7433b30 100644
--- a/crates/agent-gui/src-tauri/src/commands/app/update.rs
+++ b/crates/agent-gui/src-tauri/src/commands/app/update.rs
@@ -292,8 +292,9 @@ fn selected_release_candidates_from_entries(
 }
 
 fn github_client() -> Result<reqwest::Client, String> {
-    // 系统代理启用时更新检查随之走代理（GitHub 直连常不可达）。
-    crate::services::system_proxy::client_builder()?
+    // 应用代理启用时更新检查随之走应用代理；未启用时回退 reqwest 默认代理探测
+    // （OS 代理环境变量/系统代理设置），无系统代理即直连，尽可能保证 GitHub 可达。
+    crate::services::system_proxy::client_builder_with_os_proxy_fallback()?
         .timeout(Duration::from_secs(20))
         .build()
         .map_err(|error| format!("failed to create GitHub client: {error}"))
@@ -452,12 +453,12 @@ fn build_updater(
         builder = builder.pubkey(public_key);
     }
 
-    // 更新下载/安装与 github_client() 的探测请求保持同一份应用代理配置；未启用时
-    // 显式 no_proxy()，避免插件内部 client 兜底读取 OS 代理环境变量。
-    builder = match crate::services::system_proxy::current_proxy_url()? {
-        Some(proxy_url) => builder.proxy(proxy_url),
-        None => builder.no_proxy(),
-    };
+    // 更新下载/安装与 github_client() 的探测请求保持同一份代理语义：应用代理
+    // 启用时显式走应用代理；未启用时不调 no_proxy()，让插件内部 client 走
+    // reqwest 默认代理探测（OS 代理环境变量/系统代理设置），无系统代理即直连。
+    if let Some(proxy_url) = crate::services::system_proxy::current_proxy_url()? {
+        builder = builder.proxy(proxy_url);
+    }
 
     builder
         .endpoints(vec![manifest_url])
diff --git a/crates/agent-gui/src-tauri/src/services/system_proxy.rs b/crates/agent-gui/src-tauri/src/services/system_proxy.rs
index 8534f8cf5..c5af7348c 100644
--- a/crates/agent-gui/src-tauri/src/services/system_proxy.rs
+++ b/crates/agent-gui/src-tauri/src/services/system_proxy.rs
@@ -3,6 +3,9 @@
 //! MCP http/sse transport、Hook / Cron HTTP、网络自检、Image.url 读取）按需读取。
 //! reqwest 侧与 shell env 共用 NO_PROXY_DEFAULT：环回地址永不走代理。
 //! 凭据绝不进入日志与错误信息（只输出 host:port）。
+//! 例外：GitHub 更新链路在应用代理未启用时不做 no_proxy() 收口，而是回退
+//! reqwest 默认代理探测（OS 代理环境变量/系统代理设置），见
+//! `client_builder_with_os_proxy_fallback()`。
 
 use percent_encoding::{utf8_percent_encode, NON_ALPHANUMERIC};
 use serde_json::Value;
@@ -274,8 +277,21 @@ pub fn cached_client() -> Result<reqwest::Client, String> {
     Ok(client)
 }
 
-pub fn client_builder() -> Result<reqwest::ClientBuilder, String> {
-    async_client_builder_for_mode(&current_snapshot().mode)
+fn os_proxy_fallback_builder_for_mode(mode: &ProxyMode) -> Result<reqwest::ClientBuilder, String> {
+    match mode {
+        // 不调 no_proxy()：保留 reqwest 默认代理探测（OS 代理环境变量与
+        // macOS/Windows 系统代理设置，system-proxy 默认特性），无系统代理即直连。
+        ProxyMode::Disabled => Ok(reqwest::Client::builder()),
+        mode => async_client_builder_for_mode(mode),
+    }
+}
+
+/// GitHub 更新链路专用：应用代理启用时与其他出网点一致走应用代理（配置无效
+/// 同样 fail fast）；未启用时回退 OS 系统代理探测而不是强制直连，尽可能保证
+/// GitHub 更新地址可达。其余出网点仍用 `cached_client()`/
+/// `blocking_client_builder()` 的显式 no_proxy 语义。
+pub fn client_builder_with_os_proxy_fallback() -> Result<reqwest::ClientBuilder, String> {
+    os_proxy_fallback_builder_for_mode(&current_snapshot().mode)
 }
 
 pub fn blocking_client_builder() -> Result<reqwest::blocking::ClientBuilder, String> {
@@ -283,10 +299,12 @@ pub fn blocking_client_builder() -> Result<reqwest::blocking::ClientBuilder, Str
 }
 
 /// Resolved proxy URL for consumers that configure their own HTTP client rather
-/// than using `client_builder()`/`cached_client()` (e.g. `tauri-plugin-updater`,
-/// which only accepts a `Url` on its builder). `Ok(None)` means the app proxy is
-/// disabled — callers must still explicitly disable their own client's proxy in
-/// that case instead of leaving it to fall back to OS proxy env vars.
+/// than using `cached_client()`/`blocking_client_builder()` (e.g.
+/// `tauri-plugin-updater`, which only accepts a `Url` on its builder).
+/// `Ok(None)` means the app proxy is
+/// disabled — the GitHub update path deliberately leaves its client on reqwest's
+/// default proxy detection then (OS proxy env vars / system proxy settings),
+/// mirroring `client_builder_with_os_proxy_fallback()`.
 pub fn current_proxy_url() -> Result<Option<reqwest::Url>, String> {
     match current_snapshot().mode {
         ProxyMode::Disabled => Ok(None),
@@ -364,10 +382,22 @@ mod tests {
             assert!(matches!(mode, ProxyMode::Invalid(_)));
             assert!(async_client_builder_for_mode(&mode).is_err());
             assert!(blocking_client_builder_for_mode(&mode).is_err());
+            // 更新链路的回退 builder 同样不许把 Invalid 静默降级为直连/系统代理。
+            assert!(os_proxy_fallback_builder_for_mode(&mode).is_err());
             assert!(shell_proxy_envs_for_mode(&mode).is_err());
         }
     }
 
+    #[test]
+    fn os_proxy_fallback_builder_accepts_disabled_and_enabled_modes() {
+        assert!(os_proxy_fallback_builder_for_mode(&ProxyMode::Disabled).is_ok());
+        let enabled = parse_proxy_mode(Some(&json!({
+            "enabled": true, "type": "http", "host": "proxy.local", "port": 8080
+        })));
+        assert!(matches!(enabled, ProxyMode::Enabled(_)));
+        assert!(os_proxy_fallback_builder_for_mode(&enabled).is_ok());
+    }
+
     #[test]
     fn proxy_mode_equality_drives_set_config_dedupe() {
         let config = json!({