fix: close browser session lifecycle gaps

apps/web/tests/api.test.ts

@@ -0,0 +1,34 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { HarnessApi } from "../src/api/harness-api.js";
+
+afterEach(() => vi.unstubAllGlobals());
+
+describe("HarnessApi request headers", () => {
+  it("does not claim an empty POST contains JSON", async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response(JSON.stringify({
+      sessionId: "ses_1",
+      requestId: "req_1",
+    }), { status: 201, headers: { "Content-Type": "application/json" } }));
+    vi.stubGlobal("fetch", fetchMock);
+
+    await new HarnessApi().createSession();
+
+    const request = fetchMock.mock.calls[0]?.[1] as RequestInit;
+    expect(new Headers(request.headers).has("Content-Type")).toBe(false);
+    expect(request.body).toBeUndefined();
+  });
+
+  it("sets JSON content type when a structured body is present", async () => {
+    const fetchMock = vi.fn().mockResolvedValue(new Response(JSON.stringify({
+      runId: "run_1",
+      requestId: "req_1",
+    }), { status: 202, headers: { "Content-Type": "application/json" } }));
+    vi.stubGlobal("fetch", fetchMock);
+
+    await new HarnessApi().sendMessage("ses_1", { text: "hello", attachmentIds: [] });
+
+    const request = fetchMock.mock.calls[0]?.[1] as RequestInit;
+    expect(new Headers(request.headers).get("Content-Type")).toBe("application/json");
+    expect(request.body).toBe(JSON.stringify({ text: "hello", attachmentIds: [] }));
+  });
+});