backend, web: support for resuming streams

server/tests/active-streams.test.ts

@@ -0,0 +1,34 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { ActiveSseStream, type SseStreamEvent } from "../src/active-streams.js";
+
+test("ActiveSseStream replays buffered events to late subscribers", () => {
+  const stream = new ActiveSseStream();
+  stream.emit("delta", { text: "hel" });
+  stream.emit("delta", { text: "lo" });
+
+  const events: SseStreamEvent[] = [];
+  const unsubscribe = stream.subscribe((event) => events.push(event));
+  unsubscribe();
+
+  assert.deepEqual(events, [
+    { event: "delta", data: { text: "hel" } },
+    { event: "delta", data: { text: "lo" } },
+  ]);
+});
+
+test("ActiveSseStream replays terminal events after completion", async () => {
+  const stream = new ActiveSseStream();
+  stream.emit("delta", { text: "done" });
+  stream.complete({ event: "done", data: { text: "done" } });
+  await stream.done;
+
+  const events: SseStreamEvent[] = [];
+  stream.subscribe((event) => events.push(event));
+
+  assert.equal(stream.isCompleted, true);
+  assert.deepEqual(events, [
+    { event: "delta", data: { text: "done" } },
+    { event: "done", data: { text: "done" } },
+  ]);
+});