Replace the in-process AsyncFunction engine with Rune.execute. MCP tools
are exposed as a host-tool tree (tools.<server>.<tool>) plus top-level
search/describe; each call is permission-gated and coerced to the
{ result, attachments? } envelope. Raise data limits for base64 media.
This adds real sandboxing: host globals are isolated and runaway loops
terminate via the operation limit instead of hanging the event loop.
Aiden Cline
71ffc73272