dsh-agent-preset-switcher

In DSH, an agent preset defines a session tool catalog, system prompt, and capability boundary. Officially, once a session starts the preset is locked: the browser RPC returns a lock error for started sessions because historical tool calls would be incompatible with a new composition. If you need to change the tool set or prompt strategy mid-conversation, you must close and recreate the session, losing all context.

dsh-agent-preset-switcher moves the switch moment from request arrival to the step boundary (after one model request finishes, before the next is assembled), reusing the full official AgentPresets.recompose() mechanism. The entry point is the /mode slash command: /mode list shows the current preset and the full roster, /mode requests a switch. The switch never interrupts the current request; it takes effect at the next step boundary, and the transcript history remains intact.

Ideal for developers who need to adjust tool catalogs, prompts, or capabilities in long-running sessions, or for users who want to quickly experiment with different preset scenarios on the same conversation thread. Subagent sessions cannot be switched (their composition follows the parent), concurrent switches within a session are serialized via a per-session promise chain, and on failure the original composition is preserved and execution continues.