Actor-served files: /actor/<id>/fs/

File operations under /actor/<id>/fs/ become messages from `fs` to <id>
(fs_read, fs_write, fs_mkdir, fs_remove, fs_rename) with a 10 s timeout.
vfs.rs wraps the wasi:filesystem implementation of wasmtime-wasi.

cli/tests/host.rs

@@ -216,6 +216,36 @@ async fn actors_can_read_but_not_write_other_actor_data() {
     host.stop().await;
 }
 
+#[tokio::test]
+async fn actors_serve_files_under_fs() {
+    // "writer" serves its fs/ from memory (toolbox fs_read / fs_write / fs_remove).
+    let (_, host, mut mailbox) = filesystem_world("actor-fs").await;
+    let file = "/actor/writer/fs/notes/a.txt";
+    let write = json!({"type": "write", "path": file, "text": "hello"});
+    ask_type(&host, &mut mailbox, "reader", write, "ok").await;
+    // The write reached the owner as one fs_write message.
+    let direct = json!({"type": "fs_read", "path": "/notes/a.txt"});
+    let served = ask_type(&host, &mut mailbox, "writer", direct, "fs_file").await;
+    assert_eq!(served.body["text"], "hello");
+
+    let read = json!({"type": "read", "path": file});
+    assert_eq!(ask_type(&host, &mut mailbox, "reader", read, "content").await.body["text"], "hello");
+    let list = json!({"type": "list", "path": "/actor/writer/fs/notes"});
+    assert_eq!(ask_type(&host, &mut mailbox, "reader", list, "entries").await.body["names"], json!(["a.txt"]));
+    let root = json!({"type": "list", "path": "/actor/writer/fs"});
+    assert_eq!(ask_type(&host, &mut mailbox, "reader", root, "entries").await.body["names"], json!(["notes"]));
+
+    // fs_error and undeliverable become errors of the file operation.
+    for path in ["/actor/writer/fs/missing.txt", "/actor/nobody/fs/x"] {
+        ask_type(&host, &mut mailbox, "reader", json!({"type": "read", "path": path}), "error").await;
+    }
+    // An actor that does not answer (here: it is busy reading itself) fails after the timeout.
+    let id = host.broker.send("console", Some("reader"), None, None, json!({"type": "read", "path": "/actor/reader/fs/x"}));
+    let timed_out = receive_reply(&mut mailbox, &id, Duration::from_secs(20)).await;
+    assert_eq!(timed_out.body["type"], "error");
+    host.stop().await;
+}
+
 #[tokio::test]
 async fn files_are_plain_posix_files() {
     let (_, host, mut mailbox) = filesystem_world("posix").await;