feat: Tier-1 Model Manager with Hot-Swapping, HF Download Engine, bug fixes, and test repairs

- Phase 4: Hugging Face Download Engine — streaming GGUF downloads with progress, cancellation, and managed-model storage
- Phase 5: Model Source Validation — source-mode compatibility, path/file validation, inline error UI with recovery guidance
- Hot-swap: stop runtime → update model_path → restart atomic command
- Model library: folder open, delete model file, local model management
- SettingsPage unified hub: local models list + HF search with 3-state action buttons
- Bug fixes: send button text restored (4 failing tests), reasoning-toggle aria-label, Rust warnings
- All 89 tests passing, cargo check clean

tauri-app/src/features/runtime/useModelDownload.test.tsx

@@ -0,0 +1,156 @@
+/* @vitest-environment jsdom */
+
+import { createRoot, type Root } from "react-dom/client";
+import { act } from "react-dom/test-utils";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { HUGGING_FACE_DOWNLOAD_EVENT, type HuggingFaceDownloadProgress } from "./api";
+import { useModelDownload } from "./useModelDownload";
+
+const invokeMock = vi.fn();
+const listenMock = vi.fn();
+
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: (...args: unknown[]) => invokeMock(...args),
+}));
+
+vi.mock("@tauri-apps/api/event", () => ({
+  listen: (...args: unknown[]) => listenMock(...args),
+}));
+
+function Harness({ token = "hf_token" }: { token?: string }) {
+  const state = useModelDownload(token);
+
+  return (
+    <div>
+      <output id="is-downloading">{String(state.isDownloading)}</output>
+      <output id="progress">{state.progress.toFixed(1)}</output>
+      <output id="speed">{state.speed.toFixed(1)}</output>
+      <output id="downloaded">{state.downloaded.toFixed(1)}</output>
+      <output id="total">{state.total.toFixed(1)}</output>
+      <output id="active-file">{state.activeFile ?? ""}</output>
+      <output id="error">{state.error ?? ""}</output>
+      <button id="start" onClick={() => void state.startDownload("microsoft/phi-4", "phi-4-q4.gguf")}>
+        Start
+      </button>
+      <button id="cancel" onClick={() => void state.cancelDownload()}>
+        Cancel
+      </button>
+    </div>
+  );
+}
+
+describe("useModelDownload", () => {
+  let container: HTMLDivElement;
+  let root: Root;
+  let progressListener: ((event: { payload: HuggingFaceDownloadProgress }) => void) | null = null;
+
+  beforeEach(() => {
+    // @ts-expect-error React test environment flag
+    globalThis.IS_REACT_ACT_ENVIRONMENT = true;
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+    invokeMock.mockReset();
+    listenMock.mockReset();
+    progressListener = null;
+    listenMock.mockImplementation(async (eventName, callback) => {
+      if (eventName === HUGGING_FACE_DOWNLOAD_EVENT) {
+        progressListener = callback as (event: { payload: HuggingFaceDownloadProgress }) => void;
+      }
+      return () => undefined;
+    });
+  });
+
+  afterEach(() => {
+    act(() => root.unmount());
+    container.remove();
+    // @ts-expect-error React test environment flag
+    globalThis.IS_REACT_ACT_ENVIRONMENT = false;
+  });
+
+  it("starts a Hugging Face download with the active token and tracks progress events", async () => {
+    invokeMock.mockResolvedValue("download-1");
+
+    await act(async () => {
+      root.render(<Harness token="hf_secret" />);
+    });
+
+    await act(async () => {
+      (container.querySelector("#start") as HTMLButtonElement).click();
+      await Promise.resolve();
+    });
+
+    expect(invokeMock).toHaveBeenCalledWith("start_hugging_face_download_command", {
+      repo: "microsoft/phi-4",
+      fileName: "phi-4-q4.gguf",
+      token: "hf_secret",
+    });
+    expect(container.querySelector("#is-downloading")?.textContent).toBe("true");
+    expect(container.querySelector("#active-file")?.textContent).toBe("microsoft/phi-4:phi-4-q4.gguf");
+
+    await act(async () => {
+      progressListener?.({
+        payload: {
+          downloadId: "download-1",
+          repo: "microsoft/phi-4",
+          fileName: "phi-4-q4.gguf",
+          phase: "progress",
+          progressPercentage: 37.5,
+          downloadedMB: 768,
+          totalMB: 2048,
+          downloadSpeed: 12.4,
+          destinationPath: null,
+          message: null,
+          error: null,
+        },
+      });
+    });
+
+    expect(container.querySelector("#progress")?.textContent).toBe("37.5");
+    expect(container.querySelector("#speed")?.textContent).toBe("12.4");
+    expect(container.querySelector("#downloaded")?.textContent).toBe("768.0");
+    expect(container.querySelector("#total")?.textContent).toBe("2048.0");
+  });
+
+  it("ignores progress for stale downloads and cancels the active one", async () => {
+    invokeMock.mockResolvedValueOnce("download-1").mockResolvedValueOnce(undefined);
+
+    await act(async () => {
+      root.render(<Harness />);
+    });
+
+    await act(async () => {
+      (container.querySelector("#start") as HTMLButtonElement).click();
+      await Promise.resolve();
+    });
+
+    await act(async () => {
+      progressListener?.({
+        payload: {
+          downloadId: "download-stale",
+          repo: "other/repo",
+          fileName: "other.gguf",
+          phase: "progress",
+          progressPercentage: 90,
+          downloadedMB: 90,
+          totalMB: 100,
+          downloadSpeed: 4,
+          destinationPath: null,
+          message: null,
+          error: null,
+        },
+      });
+    });
+
+    expect(container.querySelector("#progress")?.textContent).toBe("0.0");
+
+    await act(async () => {
+      (container.querySelector("#cancel") as HTMLButtonElement).click();
+      await Promise.resolve();
+    });
+
+    expect(invokeMock).toHaveBeenLastCalledWith("cancel_hugging_face_download_command", {
+      downloadId: "download-1",
+    });
+  });
+});