brokerd, memoryd, gatewayd: a lock file keeps each to one instance

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

crates/memoryd/src/main.rs

@@ -5,6 +5,7 @@ use std::path::PathBuf;
 use std::process::ExitCode;
 use std::sync::Arc;
 
+use bxcore::instance;
 use memoryd::config::Config;
 use memoryd::serve;
 
@@ -24,6 +25,17 @@ fn main() -> ExitCode {
             return ExitCode::from(1);
         }
     };
+    // One memoryd per home (M5b spec, section 9a). The lock comes before anything under the home
+    // is made or bound, so a second copy never takes the sockets of the one that runs. Held until
+    // the process ends.
+    let lock_path = config.paths.home.join("run/memoryd.lock");
+    let _instance = match instance::lock(&lock_path) {
+        Ok(held) => held,
+        Err(e) => {
+            eprintln!("{}", e.line("memoryd", &lock_path));
+            return ExitCode::from(1);
+        }
+    };
     let log: serve::Log = Arc::new(|line: &str| eprintln!("{line}"));
     let running = match serve::start(config, log) {
         Ok(running) => running,