Plan Mode system reminder persists for entire conversation after switching back to Build mode #24121

Description

Once Plan Mode is activated (via Tab) and then deactivated (via Tab again), the Plan Mode system reminder continues to be injected into every subsequent message for the remainder of the conversation. The model cannot write or edit any files even though the UI shows Build mode is active.

Expected behavior
Switching back to Build mode should stop injecting the Plan Mode system reminder. File writes and edits should work normally.

Actual behavior
The system reminder CRITICAL: Plan mode ACTIVE - you are in READ-ONLY phase continues to be appended to every user message for the rest of the conversation. The only workaround is starting a completely new conversation.

Impact
Any work done in Plan mode is lost for that session — the user must start a new conversation and manually re-establish context to actually execute.

Plugins

No response

OpenCode version

1.14.22

Steps to reproduce

To reproduce

1. Start a conversation in Build mode
2. Press Tab to switch to Plan mode
3. Send a message (plan mode reminder gets injected)
4. Press Tab to switch back to Build mode
5. Ask the model to create or edit a file
6. Model refuses — plan mode system reminder is still being injected on every message

Screenshot and/or share link

No response

Operating System

OS: Windows (WSL)

Terminal

Windows Terminal