Agent unable to save due to malformed write payload #12412

Description

Started a new project and have been trying to formulate a proper Plan (as people always suggest). I first made a PLAN.md from another agent. That is the only file in the project, other than .opencode having been created by opencode.

Upon attempting to save the plan (to .opencode/plan/****.md) it fails every time. Somehow the payload to the write tool is always malformed.

• It seems to try to indicate the filePath twice, and the second instance is escaped improperly. <- causing the JSON parse error
• The path it was intending to write to is incorrect. My working directory for the project is /home/amatecha/git/myproject (and that is where I launched opencode from), but the logged filePath is /home/amatecha/.opencode/plans/gateway-development-plan.md for some reason. It should have been /home/amatecha/git/myproject/.opencode/plans/gateway-development-plan.md

Example:

  ⚙ invalid [tool=write, error=Invalid input for tool write: JSON parsing failed: Text:{"content":"exampletext","filePath":"/home/amatecha/.opencode/plans/gateway-development-plan.md","filePath"/home/amatecha/.opencode/plans/gateway-development-plan.md"}.
Error message: JSON Parse error: Unrecognized token '/']

(note I replaced the plan text with "exampletext" above. The length of the string previously there was 16663 bytes, if that's relevant)

Installed opencode via shell script install method. I have the following feature flag in my .bashrc:

export OPENCODE_EXPERIMENTAL_PLAN_MODE=1

I'm using qwen3-coder-next via llama.cpp if that's relevant.

Plugins

none that I know of

OpenCode version

1.1.53 (happened in 1.1.51 as well)

Steps to reproduce

1.have Experimental Plan mode enabled
2. create a new dir
3. cd into dir
4. run opencode
5. go to Plan mode and come up with a quick plan
6. tell the agent to save the plan and confirm whatever filename it suggests
7. note the failure to save due to above-described error

Screenshot and/or share link

No response

Operating System

Linux Mint 22

Terminal

xfce4-terminal