fix: correct ChatGPT OAuth GPT-5 max output token defaults (#9592)

fix: align ChatGPT OAuth GPT-5 max output token defaults

Update ChatGPT OAuth provider defaults so GPT-5 family models report 128k max output tokens based on current OpenAI model docs, avoiding incorrect 16k values in /v1/models responses.

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Co-authored-by: Letta <noreply@letta.com>

letta/schemas/providers/chatgpt_oauth.py

@@ -310,15 +310,21 @@ class ChatGPTOAuthProvider(Provider):
             )
 
     def get_default_max_output_tokens(self, model_name: str) -> int:
-        """Get the default max output tokens for ChatGPT models."""
+        """Get the default max output tokens for ChatGPT models.
+
+        References:
+        - https://developers.openai.com/api/docs/models/gpt-5
+        - https://developers.openai.com/api/docs/models/gpt-5-codex
+        - https://developers.openai.com/api/docs/models/gpt-5.1-codex-max
+        """
+        # GPT-5 family (gpt-5, gpt-5.x, codex variants): 128k max output tokens
+        if "gpt-5" in model_name:
+            return 128000
         # Reasoning models (o-series) have higher limits
         if model_name.startswith("o1") or model_name.startswith("o3") or model_name.startswith("o4"):
             return 100000
-        # GPT-5.x models
-        elif "gpt-5" in model_name:
-            return 16384
         # GPT-4 models
-        elif "gpt-4" in model_name:
+        if "gpt-4" in model_name:
             return 16384
         return 4096