Plan/build mode auto-toggles every turn, spamming reminders and burning tokens #42764

Description

In OpenCode TUI 1.15.13 on Windows, the operational mode automatically toggles between plan and build on every turn, producing a "Your operational mode has changed from plan to build" system reminder each turn.

This started after installing @plannotator/opencode with workflow: "plan-agent", but it CONTINUES after completely removing the plugin (removed from opencode.jsonc, deleted ~/.cache/opencode/packages/@plannotator, no processes left) and restarting the TUI 5 times.

Impact

The agent reacts to each auto-generated system reminder with a short empty reply ("ready"/"waiting"), which spams the user AND burns tokens on every turn - over a long session these empty generations can exhaust the entire token budget.

Expected behavior

Mode should change only via the Tab key (or an explicit command), not automatically on every turn.

Steps to reproduce

1. Open any project in OpenCode TUI on Windows.
2. Send a few messages.
3. Observe the mode indicator (bottom-right) toggling plan <-> build by itself, with a system reminder injected each turn.

Environment

• OpenCode: 1.15.13
• OS: Windows (PowerShell 5.1)
• Plugins: caveman-opencode-plugin (plannotator removed)

Additional context

Issue persists after removing plannotator, so it appears to be core OpenCode behavior (or state retained from the plugin), not the plugin itself