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/lib.rs

@@ -12,6 +12,7 @@ mod journal;
 mod locks;
 mod native;
 mod process;
+mod restart;
 mod routing;
 pub mod runtime;
 mod services;