fix: exhaustive Statement match for concurrency variants (restores build)

src/ast/visitor.rs

@@ -74,7 +74,10 @@ pub fn walk_statement<V: Visitor>(v: &mut V, stmt: &Statement) {
             for s in &c.body { v.visit_statement(s); }
         }
         Statement::Expression(e) => v.visit_expr(&e.node),
-        Statement::WorkerSpawn(_) | Statement::Complain(_)
+        Statement::SendMessage(s) => v.visit_expr(&s.message.node),
+        Statement::WorkerSpawn(_) | Statement::ReceiveMessage(_)
+        | Statement::AwaitWorker(_) | Statement::CancelWorker(_)
+        | Statement::Complain(_)
         | Statement::Break(_) | Statement::Continue(_) => {}
         Statement::EmoteAnnotated(e) => v.visit_statement(&e.statement),
         Statement::Decide(d) => {

src/interpreter/mod.rs

@@ -515,6 +515,30 @@ impl Interpreter {
                 Ok(Value::Unit)
             }
 
+            Statement::SendMessage(send) => Err(RuntimeError::new(format!(
+                "Worker-addressed message passing is not implemented: cannot `send` to worker '{}'. \
+                 Use a channel created in the main scope and pass it to the worker instead.",
+                send.target
+            ))),
+
+            Statement::ReceiveMessage(recv) => Err(RuntimeError::new(format!(
+                "Worker-addressed message passing is not implemented: cannot `receive` from worker '{}'. \
+                 Use a channel created in the main scope and pass it to the worker instead.",
+                recv.source
+            ))),
+
+            Statement::AwaitWorker(await_worker) => Err(RuntimeError::new(format!(
+                "Awaiting a worker by name is not implemented: cannot `await` worker '{}'. \
+                 Workers run detached; synchronise via a channel created in the main scope.",
+                await_worker.worker_name
+            ))),
+
+            Statement::CancelWorker(cancel) => Err(RuntimeError::new(format!(
+                "Cancelling a worker by name is not implemented: cannot `cancel` worker '{}'. \
+                 Workers run detached and cannot currently be cancelled.",
+                cancel.worker_name
+            ))),
+
             Statement::Complain(complain) => Err(RuntimeError {
                 message: complain.message.clone(),
             }),

src/sexpr.rs

@@ -331,6 +331,20 @@ fn stmt_to_sexpr(stmt: &Statement, out: &mut String, indent: usize) {
         Statement::WorkerSpawn(w) => {
             out.push_str(&format!("(spawn-worker \"{}\")", w.worker_name));
         }
+        Statement::SendMessage(s) => {
+            out.push_str(&format!("(send :to \"{}\" ", s.target));
+            expr_to_sexpr(&s.message.node, out, indent + 2);
+            out.push(')');
+        }
+        Statement::ReceiveMessage(r) => {
+            out.push_str(&format!("(receive :from \"{}\")", r.source));
+        }
+        Statement::AwaitWorker(a) => {
+            out.push_str(&format!("(await-worker \"{}\")", a.worker_name));
+        }
+        Statement::CancelWorker(c) => {
+            out.push_str(&format!("(cancel-worker \"{}\")", c.worker_name));
+        }
         Statement::Complain(c) => {
             out.push_str(&format!("(complain \"{}\")", c.message));
         }
@@ -710,6 +724,23 @@ fn stmt_to_json(stmt: &Statement) -> serde_json::Value {
             "type": "spawn_worker",
             "name": w.worker_name
         }),
+        Statement::SendMessage(s) => serde_json::json!({
+            "type": "send_message",
+            "target": s.target,
+            "message": expr_to_json(&s.message.node)
+        }),
+        Statement::ReceiveMessage(r) => serde_json::json!({
+            "type": "receive_message",
+            "source": r.source
+        }),
+        Statement::AwaitWorker(a) => serde_json::json!({
+            "type": "await_worker",
+            "name": a.worker_name
+        }),
+        Statement::CancelWorker(c) => serde_json::json!({
+            "type": "cancel_worker",
+            "name": c.worker_name
+        }),
         Statement::Complain(c) => serde_json::json!({
             "type": "complain",
             "message": c.message