feat: integrate Pi backend and Pi Web

pi/packages/coding-agent/test/suite/regressions/tree-during-streaming.test.ts

@@ -0,0 +1,35 @@
+import { fauxAssistantMessage } from "@earendil-works/pi-ai";
+import { describe, expect, it } from "vitest";
+import { userMsg } from "../../utilities.ts";
+import { createHarness } from "../harness.ts";
+
+describe("tree navigation during an active response", () => {
+	it("rejects navigation without changing the active leaf", async () => {
+		const harness = await createHarness();
+		const targetId = harness.sessionManager.appendMessage(userMsg("first"));
+		let navigationResult: unknown;
+		let leafUnchanged = false;
+
+		try {
+			// Navigate from inside the response factory, while the run is active.
+			harness.setResponses([
+				async () => {
+					const activeLeafId = harness.sessionManager.getLeafId();
+					navigationResult = await harness.session
+						.navigateTree(targetId, { summarize: false })
+						.catch((error) => error);
+					leafUnchanged = activeLeafId !== targetId && harness.sessionManager.getLeafId() === activeLeafId;
+					return fauxAssistantMessage("response");
+				},
+			]);
+			await harness.session.prompt("second");
+
+			expect(navigationResult).toEqual(
+				new Error("Wait for the current response to finish before navigating the session tree."),
+			);
+			expect(leafUnchanged).toBe(true);
+		} finally {
+			harness.cleanup();
+		}
+	});
+});