GPT-5.2: hard 10KB tool-output truncation breaks full file reads and MCP results

Issue

The GPT-5.2 harness enforces a fixed bytes truncation policy (TruncationPolicy::Bytes(10_000)). This truncates shell output and MCP responses at ~10KB, which often makes MCP tools get truncated and prevents reading common >10KB files in one call.

Raising the max token limit doesn’t help if the system prompt still tells the agent outputs are capped at 10KB.

What I tested

The system guidance includes a line like “command line output will be truncated after 10KB regardless…”. When I remove that line (leaving the rest of the shell guidance intact), the model does not start spewing huge outputs. It usually keeps reads focused (uses rg, narrow ranges, asks for specific sections) and only requests larger output when needed. Therefore, the model is already fitted well for the Codex agentic workflow where large commands should be truncated by the model, therefore this guidance is largely unnecessary.

Request

Please adjust the truncation policy to tokens so we can use GPT-5.2 to the fullest.

Additional information

_No response_