World folder is the source of truth

- actor/<id>/ holds actor.wasm, actor.json, source/, public/, data/, versions/
- the broker boots by scanning actor/; a changed actor.wasm is an upgrade,
  a rejected one stays in versions/ with a reason and the files come back
- /actor hides every data/ folder
- subscriptions live in the subscriber's actor.json
- cargo installs the SDK and points sausage-actor at it; no build limits
- PROTOCOL.md

cli/src/candidate.rs

@@ -110,7 +110,9 @@ pub async fn test(
 }
 
 fn start(broker: &Broker, id: &str, component: &Component, data: Option<&Path>, public: Option<&Path>) -> Result<(Instance, Scratch)> {
-    let dir = broker.world.scratch_dir().join(format!("{id}-{}-{}", world::now(), rand_suffix()));
+    static N: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
+    let n = N.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+    let dir = broker.world.scratch_dir().join(format!("{id}-{}-{n}", std::process::id()));
     let scratch = Scratch { dir: dir.clone() };
     std::fs::create_dir_all(dir.join("data"))?;
     std::fs::create_dir_all(dir.join("public"))?;
@@ -133,13 +135,6 @@ fn start(broker: &Broker, id: &str, component: &Component, data: Option<&Path>,
     Ok((broker.runtime.start(component, cfg)?, scratch))
 }
 
-fn rand_suffix() -> u32 {
-    use std::hash::{BuildHasher, Hasher};
-    let mut h = std::collections::hash_map::RandomState::new().build_hasher();
-    h.write_u64(std::process::id() as u64);
-    h.finish() as u32
-}
-
 async fn run_file(
     broker: &Broker,
     id: &str,