fix(gateway): carry WebUI delivery context on gateway-backed path too (Codex MUST-FIX on #3324)

#3324 moved the WebUI session/delivery context from a prefill user message into
_webui_ephemeral_system_prompt, but the gateway-backed WebUI chat path built its
own system message from the bare _WEBUI_PROGRESS_PROMPT + prefill helper — which
now returns only recall prefill. That silently dropped connected platforms, home
channels, delivery hints, and session framing on Gateway-routed WebUI chats
(same #3278 data-drop class, on the path the author missed). Build the gateway
request's system message with _webui_ephemeral_system_prompt(surface_context,
config_data=cfg) so the context is preserved. Regression test asserts the
delivery context is present in the gateway system message.

api/gateway_chat.py

@@ -247,15 +247,30 @@ def _run_gateway_chat_streaming(
         cfg = get_config()
         try:
             from api.streaming import (
-                _WEBUI_PROGRESS_PROMPT,
                 _load_webui_prefill_context,
                 _prefill_messages_with_webui_context,
                 _public_prefill_context_status,
+                _webui_ephemeral_system_prompt,
             )
 
             prefill_context = _load_webui_prefill_context(cfg)
+            # #3324: the WebUI session/delivery context (connected platforms,
+            # home channels, delivery hints, session framing) is now carried in
+            # the ephemeral system prompt rather than a prefill `user` message.
+            # The gateway-backed path must build the SAME system prompt so that
+            # context is not silently dropped on Gateway-routed WebUI chats.
+            _gateway_system_prompt = _webui_ephemeral_system_prompt(
+                None,
+                surface_context={
+                    "source": "webui",
+                    "session_id": session_id,
+                    "profile": getattr(s, "profile", None),
+                    "workspace": s.workspace if s is not None else str(workspace),
+                },
+                config_data=cfg,
+            )
             prefill_messages = [
-                {"role": "system", "content": _WEBUI_PROGRESS_PROMPT},
+                {"role": "system", "content": _gateway_system_prompt},
                 *_prefill_messages_with_webui_context(prefill_context, cfg),
             ]
             put_gateway_event("context_status", {

tests/test_webui_gateway_chat_backend.py

@@ -285,15 +285,23 @@ def test_gateway_chat_worker_translates_sse_and_persists_session(tmp_path, monke
     assert captured["headers"]["X-hermes-session-key"] == f"webui:{s.session_id}"
     assert '"stream": true' in captured["body"]
     payload = json.loads(captured["body"])
-    assert [m["content"] for m in payload["messages"]] == [
-        streaming._WEBUI_PROGRESS_PROMPT,
+    # #3324: the gateway path's first system message is now the full WebUI
+    # ephemeral system prompt (progress prompt + session/delivery context),
+    # NOT the bare _WEBUI_PROGRESS_PROMPT — otherwise the delivery/session
+    # context is silently dropped on Gateway-routed WebUI chats.
+    system_msg = payload["messages"][0]
+    assert system_msg["role"] == "system"
+    assert "Final visible assistant replies" in system_msg["content"]
+    assert "Need script" in system_msg["content"]
+    # The moved session/delivery context must be present in the system prompt.
+    assert "Connected Platforms:" in system_msg["content"]
+    assert "Delivery options for scheduled tasks:" in system_msg["content"]
+    # The recall prefill + the actual user turn follow the system message.
+    assert [m["content"] for m in payload["messages"][1:]] == [
         "prefill",
         "webui session context",
         "Say hello",
     ]
-    assert payload["messages"][0]["role"] == "system"
-    assert "Final visible assistant replies" in payload["messages"][0]["content"]
-    assert "Need script" in payload["messages"][0]["content"]
     events = []
     while not subscriber.empty():
         events.append(subscriber.get_nowait())