Spike: fs/upgrade/bench examples, agent resumes interrupted turns, world lock, short trap reasons

cli/src/main.rs

@@ -147,6 +147,11 @@ async fn run(dir: PathBuf) -> Result<()> {
     if !world.exists() {
         bail!("{} is not a Sausage world. Create one with: sausage init {}", dir.display(), dir.display());
     }
+    // One host process per world.
+    let lock = std::fs::File::create(world.root.join(".lock"))?;
+    if lock.try_lock().is_err() {
+        bail!("another sausage process runs {}", dir.display());
+    }
     let runtime = runtime::Runtime::new()?;
     let broker = Broker::new(world.clone(), runtime)?;
 
@@ -165,6 +170,7 @@ async fn run(dir: PathBuf) -> Result<()> {
     console.run_input().await;
     println!("Stopping actors …");
     broker.shutdown_all().await;
+    drop(lock);
     Ok(())
 }