fix(webui): 修复首次打开慢时多次点击导致的竞态报错

open_kimi_web_embedded 加 launch_lock 串行化并发调用，拿锁后重查单例；
oneshot 在锁内等待主线程建窗完成，封死命令返回后的残留空档。
spawned_by_me 门控失败路径的 server 清理，复用的 server 不再被误杀；
spawn 前用 try_wait 检查已有子进程避免覆盖泄漏。前端两个打开按钮加
busy 态防重入（打开中...）。

src/components/SubagentSettingsPage.tsx

@@ -162,6 +162,8 @@ export function SubagentSettingsPage({
   const [poolErrors, setPoolErrors] = useState<PoolValidationError[]>([]);
   /** Local draft for the "add pool entry" select (reset after each pick). */
   const [addSelection, setAddSelection] = useState("");
+  /** WebUI-open button in flight; disables both buttons while non-null. */
+  const [webuiBusy, setWebuiBusy] = useState<"embedded" | "browser" | null>(null);
 
   useEffect(() => {
     invoke<ExperimentalEnvStatus>("get_experimental_env_status")
@@ -371,29 +373,37 @@ export function SubagentSettingsPage({
           <div className="mt-3 flex flex-wrap gap-2">
             <button
               type="button"
+              disabled={webuiBusy !== null}
               onClick={async () => {
+                setWebuiBusy("embedded");
                 try {
                   await invoke("open_kimi_web_embedded");
                 } catch (err) {
                   alert(err instanceof Error ? err.message : String(err));
+                } finally {
+                  setWebuiBusy(null);
                 }
               }}
-              className="px-3 py-1.5 text-sm rounded bg-blue-600 text-white hover:bg-blue-500 focus:ring-2 focus:ring-blue-500 focus:outline-none"
+              className="px-3 py-1.5 text-sm rounded bg-blue-600 text-white hover:bg-blue-500 focus:ring-2 focus:ring-blue-500 focus:outline-none disabled:opacity-50 disabled:cursor-not-allowed"
             >
-              {t("openWebUIEmbedded")}
+              {webuiBusy === "embedded" ? t("webuiOpening") : t("openWebUIEmbedded")}
             </button>
             <button
               type="button"
+              disabled={webuiBusy !== null}
               onClick={async () => {
+                setWebuiBusy("browser");
                 try {
                   await invoke("open_kimi_web");
                 } catch (err) {
                   alert(err instanceof Error ? err.message : String(err));
+                } finally {
+                  setWebuiBusy(null);
                 }
               }}
-              className="px-3 py-1.5 text-sm border border-border rounded hover:bg-hover-2 focus:ring-2 focus:ring-blue-500 focus:outline-none"
+              className="px-3 py-1.5 text-sm border border-border rounded hover:bg-hover-2 focus:ring-2 focus:ring-blue-500 focus:outline-none disabled:opacity-50 disabled:cursor-not-allowed"
             >
-              {t("openWebUIBrowser")}
+              {webuiBusy === "browser" ? t("webuiOpening") : t("openWebUIBrowser")}
             </button>
           </div>
         </Card>

src/i18n/en.ts

@@ -528,6 +528,7 @@ export const enTranslations: Record<TranslationKey, string> = {
     "Open the new Web UI in an independent in-app window, or in your system browser (built into kimi-code 0.33+). Requires the kimi CLI on PATH.",
   openWebUIEmbedded: "Open in App",
   openWebUIBrowser: "Open in Browser",
+  webuiOpening: "Opening...",
 
   // Plugin marketplace
   pluginMarketplace: "Plugin Marketplace",

src/i18n/zh.ts

@@ -520,6 +520,7 @@ export const zhTranslations = {
     "以独立窗口在应用内打开新版 Web 界面，也可以选择在系统浏览器打开（kimi-code 0.33+ 内置 code-app；需要 kimi 命令在 PATH 中）。",
   openWebUIEmbedded: "在应用内打开",
   openWebUIBrowser: "在浏览器打开",
+  webuiOpening: "打开中...",
 
   // Plugin marketplace
   pluginMarketplace: "插件市场",