Plan mode (read-only) allows write operations after answering the question tool

Description

While a session is in plan mode (read-only), answering the question tool
to approve a plan does not keep writes blocked. The agent then ran Edit/Write
operations on 4 files successfully, with no rejection from the harness or
permission system, even though the plan-mode system reminder was still active.
If approving via the question tool is meant to lift read-only, the plan mode
exit must be explicit; otherwise write tools must stay blocked while plan mode
is active.

Plugins

None (no plugins installed; only the default @opencode-ai/plugin SDK dependency present in user config, no plugin entries).

OpenCode version

1.18.15

Steps to reproduce

1. Start a session in plan mode (read-only).
2. Ask the user a question via the question tool (e.g., "apply the plan?").
3. User selects an "approve" option in the question tool.
4. Ask the agent to apply the changes.
5. Observe that Edit/Write tools execute without being blocked.

Screenshot and/or share link

No response

Operating System

ubuntu 24.04.04

Terminal

Ghostty