brokerd: state.sock answers memoryd's question about a session's state

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/brokerd/src/main.rs

@@ -1,4 +1,4 @@
-//! `brokerd`: the broker role. `serve` takes the audit lock, binds both sockets, and serves.
+//! `brokerd`: the broker role. `serve` takes the audit lock, binds its three sockets, and serves.
 
 use std::ffi::OsString;
 use std::path::PathBuf;
@@ -58,6 +58,7 @@ fn main() -> ExitCode {
     // Keep the socket paths for the serving notice, before `cfg` is moved into `start`.
     let broker_path = cfg.broker_socket();
     let admin_path = cfg.admin_socket();
+    let state_path = cfg.state_socket();
 
     // The runtime and the line that says which. A `[runner]` runs calls in containers; without it,
     // every call is refused, as in M3a.
@@ -117,6 +118,7 @@ fn main() -> ExitCode {
         broker_path.display(),
         admin_path.display()
     );
+    eprintln!("brokerd: serving session state on {}", state_path.display());
     eprintln!("brokerd: {runtime_notice}");
 
     match started.run() {