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/main.rs

@@ -7,7 +7,7 @@ use clap::{Parser, Subcommand};
 use include_dir::{Dir, include_dir};
 use serde_json::json;
 
-use sausage::world::{self, VersionMeta, World};
+use sausage::world::{self, ActorMeta, VersionMeta, World};
 use sausage::{Broker, Host, cargo_actor, console, runtime};
 
 /// The source of the agent actor. `init` builds it like any other actor.
@@ -69,9 +69,8 @@ async fn init(dir: PathBuf) -> Result<()> {
     let token = setting("SAUSAGE_API_TOKEN", "API token", None)?;
 
     let world = World::create(&dir)?;
-    let mut reg = world.load_registry()?;
-    reg.subscriptions.entry("agent".into()).or_default().insert("console".into());
-    world.save_registry(&reg)?;
+    let console = ActorMeta { subscriptions: ["agent".to_string()].into(), ..world.read_meta(console::ID) };
+    world.write_meta(console::ID, &console)?;
 
     // The agent's private configuration. Only the agent can read /data.
     world.ensure_actor_dirs("agent")?;
@@ -84,11 +83,11 @@ async fn init(dir: PathBuf) -> Result<()> {
         std::fs::set_permissions(&config_path, std::fs::Permissions::from_mode(0o600))?;
     }
 
-    let source = world.root.join("broker").join("seed").join("agent");
+    let source = world.scratch_dir().join("seed").join("agent");
     std::fs::create_dir_all(&source)?;
     AGENT_SOURCE.extract(&source).context("extract agent source")?;
     println!("Building the agent actor (the first build takes a few minutes) …");
-    let out = cargo_actor::Cargo::new(world.clone()).build(&source).await.context("build agent")?;
+    let out = cargo_actor::Cargo::new(world.clone())?.build(&source).await.context("build agent")?;
     println!("Built in {:.1} s.", out.seconds);
 
     let broker = Broker::new(world.clone(), runtime::Runtime::new()?)?;
@@ -99,6 +98,7 @@ async fn init(dir: PathBuf) -> Result<()> {
         built_by: Some(cargo_actor::ID.into()),
         requested_by: "init".into(),
         created_at: world::now(),
+        rejected: None,
     };
     broker.create_actor("agent", &out.wasm, Some(&source), meta, false).await?;
     println!("World ready. Start it with: sausage run {}", dir.display());