fix(exploration): flatten dict reply payloads instead of storing str(dict)

E2E on t480 showed assistant bubbles rendering {'content': '...'} because
tutu replies carry msgBody as a parsed object and the router stored
str(reply.content). Coerce to the inner text before persisting.

backend/agenteval/web/routers/exploration.py

@@ -10,6 +10,7 @@ with 409 plus a readable reason, so the rejection itself is feedback to the
 resident agent.
 """
 
+import json
 from datetime import datetime
 from typing import Any
 
@@ -61,6 +62,20 @@ class CloseSessionRequest(BaseModel):
     experience: dict[str, Any]
 
 
+def _coerce_reply_text(content: Any) -> str:
+    """Flatten a reply payload to text; tutu returns msgBody as a parsed object, and str(dict) would leak a Python repr into the view."""
+    if isinstance(content, str):
+        return content
+    if isinstance(content, dict):
+        for key in ("content", "text", "message"):
+            value = content.get(key)
+            if isinstance(value, str) and value:
+                return value
+    if content is None:
+        return ""
+    return json.dumps(content, ensure_ascii=False)
+
+
 def _check_creation_guardrails(
     campaign: Campaign,
     triggered_by: ExplorationTrigger,
@@ -283,7 +298,7 @@ async def send_session_message(
 
     received_at = utc_now()
     latency_ms = int((received_at - sent_at).total_seconds() * 1000)
-    reply_text = str(reply.content)
+    reply_text = _coerce_reply_text(reply.content)
     message_repo.save_message(
         ExplorationMessage(
             session_id=session_obj.id,

tests/integration/test_exploration_api.py

@@ -175,6 +175,37 @@ async def test_full_lifecycle_create_message_close(seeded_db, mock_channel, clie
     assert closed["closed_at"] is not None
 
 
+async def test_dict_reply_content_is_flattened_to_text(seeded_db, monkeypatch, client):
+    """通道回复 content 为对象（如 tutu msgBody）时应提取文本而非存 str(dict)。"""
+    from agenteval.channels.base import Reply
+    from tests.unit.mock_channel import MockChannel
+
+    class _DictReplyChannel(MockChannel):
+        async def poll_reply(self, question_msg_id, timeout=30.0, poll_interval=1.0):
+            return Reply(
+                question_msg_id=question_msg_id,
+                content={"content": "您好，我是客服"},
+                raw_message={},
+            )
+
+    _stub_channel_factory(monkeypatch, _DictReplyChannel(reply_text="unused"))
+
+    resp = await _create_session(client)
+    assert resp.status_code == 200, resp.text
+    session_id = resp.json()["id"]
+
+    resp = await client.post(
+        f"/api/exploration/sessions/{session_id}/messages",
+        json={"content": "你好"},
+    )
+    assert resp.status_code == 200, resp.text
+    assert resp.json()["reply"] == "您好，我是客服"
+
+    messages_resp = await client.get(f"/api/exploration/sessions/{session_id}/messages")
+    assistant = [m for m in messages_resp.json()["messages"] if m["role"] == "assistant"]
+    assert assistant[0]["content"] == "您好，我是客服"
+
+
 async def test_create_requires_existing_running_campaign(seeded_db, client):
     resp = await _create_session(client, campaign_id="nope")
     assert resp.status_code == 404