plugins: mid-turn watcher reload invalidates tool registry (Unknown tool) #40825

Summary

Plugin tools registered with codemode: true are listed in the session catalog, but calls fail with "Unknown tool" whenever a watcher-triggered plugin reload lands while that turn is in flight. The reload releases the old plugin generation's registrations, so the tool the model is already calling no longer resolves.

Environment

• opencode version: 0.0.0-next-16902
• OS: Darwin 25.6.0 (arm64)
• Terminal: ghostty (xterm-256color)
• Shell: /bin/zsh
• Install/channel: next (npm)
• Active plugins: ~/.config/opencode/plugins/goal.ts, loop.ts, moshi-hooks.ts

Reproduction

1. Add a plugin registering a tool via ctx.tool.transform with options: { codemode: true }.
2. Start a turn that will call the tool.
3. While the turn is running, edit/touch any file under ~/.config/opencode/plugins/ (the config watcher reloads all plugins).
4. Model calls the tool → runtime rejects with "Unknown tool", even though the tool is in the catalog shown to the model.

Expected Behavior

In-flight tool calls keep working; the session context reflects the post-reload tool registry (or the reload waits for the turn to finish).

Actual Behavior

Intermittent "Unknown tool" failures on exactly the plugin-provided tools, matching the timing of watcher reloads. Recovered on the next turn. Saw this twice in one session, both times tied to plugin file mtime changes mid-turn.

Additional Context

Workaround: restart the service after any plugin file edit. Nothing in the plugin API lets a plugin pin its registration across a reload, so this needs a server-side fix: e.g. reload should not release tool registrations mid-turn, or the session context/tool resolution should rebuild after reload.