Auto-compaction causes the subagent to lose its original context, possibly the system prompt as well

[gasatrya]

Description

I’m honestly frustrated, this is the second time it has happened.

I have a QA Specialist subagent whose prompt explicitly instructs it to perform only QA-related tasks. However, due to auto-compaction, it loses the original context provided by the main agent. As a result, it suddenly starts reading the planned features document and working on the next phase without my permission.

This is problematic because the subagent was specifically designed to handle QA tasks, not to build or implement new features.

How can I prevent this from happening again in the future?

OpenCode version

1.0.218

Steps to reproduce

Must have main again and subagent.

Screenshot and/or share link

Operating System

WSL 2

Terminal

Windows Terminal

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [BUG]: Subagents inappropriately inherit main agent instructions from CLAUDE.md/AGENTS.md #4483: Subagents inappropriately inherit main agent instructions from CLAUDE.md/AGENTS.md
• Model in BUILD mode does not have enough context to continue after compaction #3031: Model in BUILD mode does not have enough context to continue after compaction
• Epic: Compaction Update #4102: Epic: Compaction Update (addresses context loss and rules preservation during compaction)
• Session Todo-list is forgotten after compaction #5934: Session Todo-list is forgotten after compaction (related context loss issue)

The core issue appears to be that auto-compaction may be incompletely preserving the subagent's system prompt and specialized instructions. Issues #4483 and #4102 directly address similar problems where context or instructions are lost after compaction.

Feel free to ignore if none of these address your specific case.

[rekram1-node]

Can u share a session this happened in?

opencode export > session.json

[gasatrya]

@rekram1-node Here it is

session.json

[esau-morais]

also having similar issue, but with manual /compact. is this session context limit expected? even tho it might not be the best practice having large sessions, it is quite frustrating to lose like this