fix: preserve full chat embed mode navigation

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

@@ -3,6 +3,7 @@ import test from "node:test";
 
 import {
   buildStandardChatRedirectPath,
+  buildFullChatNavigationPath,
   buildEmbeddedIframeRedirectPath,
   buildChatsIframeRedirectPath,
   buildChatsIframeThreadPath,
@@ -280,6 +281,27 @@ test("builds a standard full-chat URL without leaking the legacy marker", () =>
   );
 });
 
+test("keeps full-chat presentation flags when the sidebar opens an agent or thread", () => {
+  assert.equal(
+    buildFullChatNavigationPath(
+      "/page/workspace/chats/new?agent=agent-1",
+      "?hideChrome=1&chatMode=full",
+    ),
+    "/page/workspace/chats/new?agent=agent-1&hideChrome=1&chatMode=full",
+  );
+  assert.equal(
+    buildFullChatNavigationPath(
+      "/page/workspace/chats/thread-123",
+      "?embed=1&theme=dark-blue&chatMode=full",
+    ),
+    "/page/workspace/chats/thread-123?embed=1&theme=dark-blue&chatMode=full",
+  );
+  assert.equal(
+    buildFullChatNavigationPath("/page/workspace/chats/new", ""),
+    "/page/workspace/chats/new",
+  );
+});
+
 test("preserves explicit Brainy iframe mode and theme across redirects", () => {
   assert.equal(
     buildChatsIframeRedirectPath("?chatMode=iframe&theme=dark-blue&ticket=secret"),

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

@@ -107,6 +107,26 @@ export function buildStandardChatRedirectPath(
   return query ? `${pathname}?${query}` : pathname;
 }
 
+/**
+ * Keep an explicitly selected standard-chat presentation while navigating
+ * between `/chats/new` and a concrete chat thread.  Without this, a click in
+ * the full-chat sidebar drops `hideChrome=1&chatMode=full`; an iframe host
+ * then looks like the legacy bare integration and is incorrectly redirected
+ * to the private AgentSelector workspace.
+ *
+ * This deliberately whitelists presentation flags through
+ * `buildStandardChatRedirectPath` instead of copying arbitrary login/query
+ * values into user-facing chat URLs.
+ */
+export function buildFullChatNavigationPath(
+  destinationPath: string,
+  search: string,
+): string {
+  return hasIframePresentationOverride(search) || isExplicitFullChatMode(search)
+    ? buildStandardChatRedirectPath(search, destinationPath)
+    : destinationPath;
+}
+
 /**
  * Preserve only the presentation parameters consumed by the iframe workspace.
  * Login credentials must never be copied into the post-login address bar.