feat: add connection state store with health polling

tests/unit/web/connection-store.test.ts

@@ -0,0 +1,101 @@
+// @vitest-environment jsdom
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+const fetchMock = vi.fn();
+vi.stubGlobal("fetch", fetchMock);
+
+import { useConnectionStore } from "@/stores/connection-store";
+
+function okHealth() {
+  return Promise.resolve(new Response(JSON.stringify({ status: "healthy" }), { status: 200 }));
+}
+
+function failHealth() {
+  return Promise.reject(new TypeError("Failed to fetch"));
+}
+
+describe("connection-store", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    useConnectionStore.setState({
+      status: "connected",
+      failedSince: null,
+      lastHealthCheck: null,
+    });
+    fetchMock.mockReset();
+  });
+
+  afterEach(() => {
+    useConnectionStore.getState().stopPolling();
+    vi.useRealTimers();
+  });
+
+  it("starts in connected state", () => {
+    expect(useConnectionStore.getState().status).toBe("connected");
+  });
+
+  it("transitions to disconnected on setDisconnected", () => {
+    useConnectionStore.getState().setDisconnected();
+    const state = useConnectionStore.getState();
+    expect(state.status).toBe("disconnected");
+    expect(state.failedSince).toBeTypeOf("number");
+  });
+
+  it("does not overwrite failedSince on repeated setDisconnected calls", () => {
+    useConnectionStore.getState().setDisconnected();
+    const first = useConnectionStore.getState().failedSince;
+    useConnectionStore.getState().setDisconnected();
+    expect(useConnectionStore.getState().failedSince).toBe(first);
+  });
+
+  it("transitions to offline on setOffline", () => {
+    useConnectionStore.getState().setOffline();
+    expect(useConnectionStore.getState().status).toBe("offline");
+  });
+
+  it("transitions from offline to disconnected on setOnline", () => {
+    useConnectionStore.getState().setOffline();
+    useConnectionStore.getState().setOnline();
+    expect(useConnectionStore.getState().status).toBe("disconnected");
+  });
+
+  it("checkHealth transitions disconnected → reconnected on success", async () => {
+    fetchMock.mockImplementation(okHealth);
+    useConnectionStore.getState().setDisconnected();
+    await useConnectionStore.getState().checkHealth();
+    expect(useConnectionStore.getState().status).toBe("reconnected");
+    expect(useConnectionStore.getState().lastHealthCheck).toBeTypeOf("number");
+  });
+
+  it("checkHealth stays disconnected on failure", async () => {
+    fetchMock.mockImplementation(failHealth);
+    useConnectionStore.getState().setDisconnected();
+    await useConnectionStore.getState().checkHealth();
+    expect(useConnectionStore.getState().status).toBe("disconnected");
+  });
+
+  it("checkHealth is a no-op when already connected", async () => {
+    fetchMock.mockImplementation(okHealth);
+    await useConnectionStore.getState().checkHealth();
+    expect(useConnectionStore.getState().status).toBe("connected");
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("startPolling is idempotent", () => {
+    useConnectionStore.getState().setDisconnected();
+    useConnectionStore.getState().startPolling();
+    useConnectionStore.getState().startPolling();
+    fetchMock.mockImplementation(failHealth);
+    vi.advanceTimersByTime(3000);
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("stopPolling clears the interval", () => {
+    useConnectionStore.getState().setDisconnected();
+    fetchMock.mockImplementation(failHealth);
+    useConnectionStore.getState().startPolling();
+    useConnectionStore.getState().stopPolling();
+    vi.advanceTimersByTime(6000);
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+});