feat(agent): 增强多模态链路与工具调用能力

backend/src/v1/agent/repository.py

@@ -107,6 +107,10 @@ class AgentRepository:
             raise HTTPException(status_code=404, detail="Session not found")
 
         next_seq = int(session_row.message_count or 0) + 1
+        if not _has_title(session_row.title):
+            session_title = _derive_session_title(content_text)
+            if session_title is not None:
+                session_row.title = session_title
         payload_metadata = dict(metadata or {})
         payload_metadata["run_id"] = run_id
         message = AgentChatMessage(
@@ -264,3 +268,14 @@ class AgentRepository:
                 if rendered:
                     payload["attachments"] = rendered
         return payload
+
+
+def _has_title(title: object) -> bool:
+    return isinstance(title, str) and bool(title.strip())
+
+
+def _derive_session_title(content_text: str) -> str | None:
+    normalized = " ".join(content_text.split())
+    if not normalized:
+        return None
+    return normalized[:80]

backend/src/v1/agent/router.py

@@ -203,6 +203,11 @@ async def stream_events(
                         user_id=str(current_user.id),
                         reason=str(exc),
                     )
+                    if "Timeout reading from" in str(exc):
+                        idle_polls += 1
+                        yield ": keep-alive\n\n"
+                        await asyncio.sleep(0.2)
+                        continue
                     break
 
                 if not rows:

backend/src/v1/agent/service.py

@@ -212,12 +212,19 @@ class AgentService:
                         content_type=mime_type,
                     )
                 except Exception:  # noqa: BLE001
-                    bucket_name = "private"
-                    stored_path = await self._attachment_storage.upload_bytes(
-                        bucket=bucket_name,
-                        path=path,
-                        content=payload,
-                        content_type=mime_type,
+                    logger.exception(
+                        "Attachment upload failed",
+                        extra={
+                            "bucket": bucket_name,
+                            "path": path,
+                            "mime_type": mime_type,
+                            "thread_id": run_input.thread_id,
+                            "run_id": run_input.run_id,
+                        },
+                    )
+                    raise HTTPException(
+                        status_code=502,
+                        detail="Failed to upload attachment",
                     )
                 attachments.append(
                     {