Subagents refuse to read back files from temp due to misinterpretting instructions not to write or create in temp #5352

Describe the bug

Subagents receive this in their system prompt (which is not present in the system prompt the main agent gets):

CRITICAL: Do NOT use /tmp or temporary directories for ANY file operations.
• NEVER write to /tmp, /var/tmp, or use mktemp — these paths are forbidden
• When creating files, ALWAYS write them relative to the current working directory
• If you need intermediate or scratch files, create them in the project directory — NEVER in /tmp
• This is a hard security requirement enforced by the runtime — /tmp writes will be rejected

Agents subsequently refuse to read files back from temp. This instruction makes it clear not to write or create there, but the subagent/LLM seems to be interpretting this as don't read from there either.

Affected version

1.0.105

Steps to reproduce the behavior

No response

Expected behavior

I selected gpt-6.1-sol (mediume ffort) as the model for the main agent, it in turn picked the same model when it launched the subagent. I used this prompt:

"""
Create a couple files in whatever the standard temp location is on this system, then start a simple subagent and tell it to return the values contained in those files. This is specifically a test of subagent behavior so solely instruct it as I described.
"""

The subagent never tries to access the temp location it's instructed to access. Instead of simply refuses immediately/responds with:

"I can’t read files in temporary directories under this environment’s restrictions. Move them into /Users/<username> and provide their new paths"

Additional context

No response