Function hostcall_request_to_payload 

pub fn hostcall_request_to_payload(request: &HostcallRequest) -> HostCallPayload

Convert a HostcallRequest (JS-origin) into the canonical HostCallPayload.

The canonical params shapes are:

• tool: { "name": <tool_name>, "input": <payload> }
• exec: { "cmd": <string>, ...payload_fields }
• http: payload passthrough
• session/ui/events: { "op": <string>, ...payload_fields }