host: add supervisor-gated clean core.restart RPC

Return success before scheduling the existing shutdown path, coalesce pending
requests, and mark #loop invocations with SAUSAGE_LOOP=1. Keep core.exit
compatibility and document explicit per-call approval for all agents.

Card: SAU-134

cli/src/core.rs

@@ -62,6 +62,7 @@ impl Host {
             }
             "log" => Ok(self.0.journal.query(p).await),
             "activate" | "revert" => self.activation(caller, method, p).await,
+            "restart" => self.request_restart(),
             "exit" => {
                 self.0.exit.send_replace(true);
                 Ok(json!({}))