Plan Mode doesn't work at all with ACP

[6112]

What happened?

When running gemini-cli via ACP in Plan Mode, the agent doesn't know where to write its plan markdown file. It tries a bunch of locations, which always gets denied by the system. It keeps doing this in a loop and gets stuck trying to write the plan.

This makes Plan Mode completely unusable(!!) in ACP clients!

Tested with Emacs agent-shell.el and VSCode ACP Client, same result in both. Tested on two different machines, macOS and Linux

What did you expect to happen?

Agent writes the plan to a valid location and doesn't run into access issues. Plan Mode is usable

Client information

Client Information

Run gemini to enter the interactive CLI, then run the /about command.

> /about
About Gemini CLI
CLI Version: 0.34.0-nightly.20260304.28af4e127-git.0486a16
Git Commit: 0486a16
Model: 3-flash-preview
Sandbox: no sandbox                                                                                                                                                   OS: linux

Login information

API key login

Anything else we need to know?

No response