fix: openai compatible layer not working

src/routes/openai.py

@@ -3,7 +3,7 @@
 from fastapi import APIRouter
 from openai.types.chat import ChatCompletionContentPartTextParam
 from promplate import Message
-from pydantic import field_serializer
+from pydantic import field_validator
 from typing_extensions import TypedDict
 
 from ..utils.llm import Model
@@ -47,12 +47,13 @@ class ChatInput(ChainInput):
     stream: bool = False
     messages: list[CompatibleMessage]  # type: ignore
 
-    @field_serializer("messages")
-    def serialize_messages(self, value: CompatibleMessage):
-        content = value["content"]
-        if isinstance(content, str):
-            return value
-        value["content"] = "".join(i["text"] for i in content)
+    @field_validator("messages", mode="after")
+    def serialize_messages(cls, value: list[CompatibleMessage]):
+        for msg in value:
+            content = msg["content"]
+            if isinstance(content, str):
+                continue
+            msg["content"] = "".join(i["text"] for i in content)
         return value
 
     @property