broker: remove op deletes an actor

{"type":"remove","actor"} shuts the actor down normally, drops its
mailbox and supervisor, and deletes /actor/<id>/. Native actors cannot
be removed. Test in cli/tests/host.rs, documented in PROTOCOL.md.

cli/src/broker.rs

@@ -1,6 +1,6 @@
 //! The broker: message routing, mailboxes, subscriptions, the version store,
 //! and the requests to `broker` (spawn, upgrade, rollback, stop, start,
-//! subscribe, unsubscribe, scan, exit). `supervisor.rs` runs each WASM actor.
+//! remove, subscribe, unsubscribe, scan, exit). `supervisor.rs` runs each WASM actor.
 //!
 //! The broker accepts only `.wasm` files. It does not know any source language.
 //! The world folder is the source of truth: `scan` boots every
@@ -351,6 +351,35 @@ impl Broker {
         Ok(result)
     }
 
+    /// Stop an actor (normal shutdown) and delete its folder `actor/<id>/`.
+    /// Afterwards the ID is unknown: messages to it are undeliverable, and
+    /// it can be spawned again from scratch.
+    pub async fn remove_actor(&self, id: &str) -> Result<Value> {
+        if NATIVE.contains(&id) {
+            bail!("{id} is part of the host and cannot be removed");
+        }
+        if !world::valid_id(id) {
+            bail!("invalid actor ID {id:?}");
+        }
+        let lock = self.op_lock(id);
+        let _guard = lock.lock().await;
+        let dir = self.world.actor_dir(id);
+        if !self.is_supervised(id) && !dir.is_dir() {
+            bail!("no actor with ID {id}");
+        }
+        if self.is_supervised(id) {
+            self.control(id, |reply| Control::Shutdown { reply }).await?;
+        }
+        // Without its mailbox, messages to `id` are undeliverable.
+        self.controls.lock().unwrap().remove(id);
+        self.mailboxes.lock().unwrap().remove(id);
+        self.metas.lock().unwrap().remove(id);
+        if dir.exists() {
+            std::fs::remove_dir_all(&dir).with_context(|| format!("delete {}", dir.display()))?;
+        }
+        Ok(json!({"type": "removed", "actor": id}))
+    }
+
     /// Boot the actors in `actor/`. Called at start and on `scan`.
     ///
     /// - An `actor.wasm` equal to the installed version starts as is.
@@ -455,6 +484,7 @@ impl Broker {
             }
             "stop" => self.control(&actor()?, |reply| Control::Stop { reply }).await,
             "start" => self.control(&actor()?, |reply| Control::Start { reply }).await,
+            "remove" => self.remove_actor(&actor()?).await,
             "subscribe" | "unsubscribe" => {
                 let publisher = actor()?;
                 let on = ty == "subscribe";
@@ -474,7 +504,7 @@ impl Broker {
                 self.exit.notify_one();
                 Ok(json!({"type": "exiting"}))
             }
-            other => bail!("unknown broker request {other:?}. Known: spawn, upgrade, rollback, stop, start, subscribe, unsubscribe, scan, exit"),
+            other => bail!("unknown broker request {other:?}. Known: spawn, upgrade, rollback, stop, start, remove, subscribe, unsubscribe, scan, exit"),
         }
     }