Add transport-neutral routing and stream contracts

tests/helpers/test-connection.ts

@@ -0,0 +1,45 @@
+import {
+  BaseStream,
+  type StreamMessage,
+} from "../../src/services/stream/base-stream.js";
+
+/** Minimal observable connection used by application and broadcaster tests. */
+export class TestConnection extends BaseStream {
+  readonly messages: StreamMessage[] = [];
+  readonly closeCallbacks: Array<() => void> = [];
+  closed = false;
+
+  constructor(
+    readonly streaming: boolean,
+    readonly bidirectional: boolean,
+  ) {
+    super();
+  }
+
+  async send(message: StreamMessage): Promise<void> {
+    if (this.closed) {
+      throw new Error("connection is closed");
+    }
+
+    this.messages.push(message);
+  }
+
+  close(): void {
+    if (this.closed) {
+      return;
+    }
+
+    this.closed = true;
+    const callbacks = this.closeCallbacks.splice(0);
+    callbacks.forEach((callback) => callback());
+  }
+
+  onClose(callback: () => void): void {
+    if (this.closed) {
+      callback();
+      return;
+    }
+
+    this.closeCallbacks.push(callback);
+  }
+}