fix(frontend): preserve iframe theme across login

The iframe login used a fixed queryless redirect and called setTheme, which both dropped the iframe theme and persisted it into the normal site's shared theme storage.

frontend-web/src/core/embed/embed-session.ts

@@ -1,3 +1,7 @@
+import { resolveEmbedThemeMode } from "./theme-mode.mjs";
+
+export { resolveEmbedThemeMode } from "./theme-mode.mjs";
+
 /**
  * 「外部系统 iframe 套用深链」相关的**按标签页**会话开关。承载三个相互独立的能力，多由 URL
  * 路由参数开启（独立会话 `isolate` 另可由「外观」设置里的开关在运行时切换，见 `setIsolatedSession`），
@@ -85,16 +89,6 @@ export function readIsolateParam(search: string): FlagParam {
   return readFlagParam(search, "isolate");
 }
 
-/**
- * 把外部传入的主题色映射成离散明/暗。与 `resolveThemeFromQuery` 同源约定（dark-blue → 深色），
- * 另外宽松接受 `dark` / 中文「深色/深蓝」直传；其余（含空）一律浅色。
- */
-export function resolveEmbedThemeMode(raw: string | null | undefined): EmbedTheme {
-  const v = (raw ?? "").trim().toLowerCase();
-  if (v === "dark" || v === "dark-blue" || v === "深色" || v === "深蓝") return "dark";
-  return "light";
-}
-
 /** 取 URL query 里的 `theme` 值（embed 主题来源）。 */
 export function readEmbedThemeParam(search: string): string {
   return (toSearchParams(search).get("theme") ?? "").trim();

frontend-web/src/core/embed/theme-mode.mjs

@@ -0,0 +1,19 @@
+/**
+ * @typedef {"light" | "dark"} EmbedThemeMode
+ */
+
+/**
+ * Map external theme names to the two themes supported by iframe surfaces.
+ *
+ * @param {string | null | undefined} rawTheme
+ * @returns {EmbedThemeMode}
+ */
+export function resolveEmbedThemeMode(rawTheme) {
+  const theme = (rawTheme ?? "").trim().toLowerCase();
+  return theme === "dark" ||
+    theme === "dark-blue" ||
+    theme === "深色" ||
+    theme === "深蓝"
+    ? "dark"
+    : "light";
+}

frontend-web/src/core/page-layout/chats-iframe-route.test.mjs

@@ -2,7 +2,10 @@ import assert from "node:assert/strict";
 import test from "node:test";
 
 import {
+  buildChatsIframeRedirectPath,
+  buildChatsIframeThreadPath,
   isChatsIframeWorkspacePath,
+  resolvePostLoginRedirectPath,
   resolveForcedThemeForPath,
 } from "./chats-iframe-route.ts";
 
@@ -48,3 +51,73 @@ test("honors the dark-blue theme query on chats_iframe routes", () => {
     "light",
   );
 });
+
+test("forces the iframe theme on the login route without changing normal login", () => {
+  assert.equal(
+    resolveForcedThemeForPath(
+      "/login",
+      "?from=iframe&theme=dark-blue",
+    ),
+    "dark",
+  );
+  assert.equal(
+    resolveForcedThemeForPath(
+      "/login/guest",
+      "?from=iframe&theme=dark-blue",
+    ),
+    "dark",
+  );
+  assert.equal(
+    resolveForcedThemeForPath("/login", "?theme=dark-blue"),
+    undefined,
+  );
+  assert.equal(
+    resolveForcedThemeForPath(
+      "/page/workspace/chats/new",
+      "?from=iframe&theme=dark-blue",
+    ),
+    undefined,
+  );
+});
+
+test("preserves the iframe theme in the post-login redirect", () => {
+  assert.equal(
+    buildChatsIframeRedirectPath("?from=iframe&theme=dark-blue"),
+    "/page/workspace/chats_iframe/new?from=iframe&theme=dark-blue",
+  );
+  assert.equal(
+    buildChatsIframeRedirectPath("?from=iframe"),
+    "/page/workspace/chats_iframe/new?from=iframe",
+  );
+  assert.equal(
+    buildChatsIframeRedirectPath(
+      "?from=iframe&theme=dark-blue&ticket=secret&authToken=secret",
+    ),
+    "/page/workspace/chats_iframe/new?from=iframe&theme=dark-blue",
+  );
+});
+
+test("keeps the iframe redirect ahead of login-method fallbacks", () => {
+  assert.equal(
+    resolvePostLoginRedirectPath(
+      "?from=iframe&theme=dark-blue&yUserId=user-1",
+      "/page/workspace/chats/new",
+    ),
+    "/page/workspace/chats_iframe/new?from=iframe&theme=dark-blue",
+  );
+  assert.equal(
+    resolvePostLoginRedirectPath("?yUserId=user-1", "/page/workspace/chats/new"),
+    "/page/workspace/chats/new",
+  );
+});
+
+test("preserves iframe theme when a new chat becomes a thread", () => {
+  assert.equal(
+    buildChatsIframeThreadPath(
+      "/page/workspace",
+      "thread-123",
+      "?from=iframe&theme=dark-blue&ticket=secret",
+    ),
+    "/page/workspace/chats_iframe/thread-123?from=iframe&theme=dark-blue",
+  );
+});

frontend-web/src/core/page-layout/chats-iframe-route.ts

@@ -1,8 +1,60 @@
-import { resolveEmbedThemeMode } from "@/core/embed/embed-session";
+import { resolveEmbedThemeMode } from "../embed/theme-mode.mjs";
+
+const CHATS_IFRAME_PATH = "/page/workspace/chats_iframe/new";
+const IFRAME_LOGIN_SOURCE = "iframe";
+
+function toSearchParams(search: string): URLSearchParams {
+  return new URLSearchParams(search.startsWith("?") ? search : `?${search}`);
+}
+
+export function isChatsIframeLogin(search: string): boolean {
+  return toSearchParams(search).get("from") === IFRAME_LOGIN_SOURCE;
+}
+
+/**
+ * Preserve only the presentation parameters consumed by the iframe workspace.
+ * Login credentials must never be copied into the post-login address bar.
+ */
+export function buildChatsIframeRedirectPath(search: string): string {
+  const source = toSearchParams(search);
+  const target = new URLSearchParams();
+
+  if (isChatsIframeLogin(search)) {
+    target.set("from", IFRAME_LOGIN_SOURCE);
+  }
+
+  const theme = source.get("theme")?.trim();
+  if (theme) {
+    target.set("theme", theme);
+  }
+
+  const query = target.toString();
+  return query ? `${CHATS_IFRAME_PATH}?${query}` : CHATS_IFRAME_PATH;
+}
+
+export function buildChatsIframeThreadPath(
+  routeBase: string,
+  threadId: string,
+  search: string,
+): string {
+  const base = routeBase.endsWith("/") ? routeBase.slice(0, -1) : routeBase;
+  const query = buildChatsIframeRedirectPath(search).split("?")[1];
+  const path = `${base}/chats_iframe/${encodeURIComponent(threadId)}`;
+  return query ? `${path}?${query}` : path;
+}
+
+export function resolvePostLoginRedirectPath(
+  search: string,
+  fallbackPath: string,
+): string {
+  return isChatsIframeLogin(search)
+    ? buildChatsIframeRedirectPath(search)
+    : fallbackPath;
+}
 
 export function isChatsIframeWorkspacePath(pathname: string): boolean {
   return (
-    pathname === "/page/workspace/chats_iframe/new" ||
+    pathname === CHATS_IFRAME_PATH ||
     pathname.startsWith("/page/workspace/chats_iframe/")
   );
 }
@@ -15,9 +67,12 @@ export function resolveForcedThemeForPath(
     return "light";
   }
 
-  if (isChatsIframeWorkspacePath(pathname)) {
-    const normalizedSearch = search.startsWith("?") ? search : `?${search}`;
-    const rawTheme = new URLSearchParams(normalizedSearch).get("theme")?.trim();
+  const isLoginPath = pathname === "/login" || pathname.startsWith("/login/");
+  if (
+    isChatsIframeWorkspacePath(pathname) ||
+    (isLoginPath && isChatsIframeLogin(search))
+  ) {
+    const rawTheme = toSearchParams(search).get("theme")?.trim();
     return rawTheme ? resolveEmbedThemeMode(rawTheme) : "light";
   }