feat: derive BUN_JSC_forceRAMSize from effective per-agent MemoryMax=

hive-c0re/src/server.rs

@@ -435,8 +435,10 @@ async fn handle_set_resource_limits(
         &hive.agent_memory_max,
     );
     Ok(HostResponse::messages(vec![format!(
-        "{name}: CPUQuota={cpu} MemoryMax={mem} (restart the container if it is running \
-         and the new caps need to take effect immediately)"
+        "{name}: CPUQuota={cpu} MemoryMax={mem} — the cgroup cap itself is live now (restart \
+         the container if it's running and needs the new cap immediately), but the derived \
+         Claude/JSC heap ceiling is baked in at build time, so it needs a REBUILD \
+         (`hivectl agents rebuild {name}`) to actually track this change"
     )]))
 }