Streamable HTTP/SSE servers from the workspace's .volcanic/mcp/servers.json.
Headers are sealed with AES-GCM; the chat and the visible fields are the
associated data, so only /mcp_add|remove|tools change servers. Tools
<server>__<tool> go live in the session. An unreachable server is skipped
and reported in the system prompt. Keys are redacted from tool results, and
Telegram deletes messages that carry one.