diff --git a/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx b/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx
new file mode 100644
index 00000000..46e57874
--- /dev/null
+++ b/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx
@@ -0,0 +1,216 @@
+// @vitest-environment jsdom
+/**
+ * FilesTab: NotAvailablePanel + FilesToolbar coverage.
+ *
+ * NotAvailablePanel: pure presentational component — renders a "feature not
+ * available" placeholder for external-runtime workspaces.
+ * FilesToolbar: pure props-driven component — directory selector, file count,
+ * action buttons (New, Upload, Export, Clear, Refresh) with correct aria-labels.
+ *
+ * No @testing-library/jest-dom import — use textContent / className /
+ * getAttribute checks to avoid "expect is not defined" errors.
+ */
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { cleanup, render, screen } from "@testing-library/react";
+import React from "react";
+
+import { FilesToolbar } from "../FilesToolbar";
+import { NotAvailablePanel } from "../NotAvailablePanel";
+
+// ─── afterEach ─────────────────────────────────────────────────────────────────
+
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+});
+
+// ─── NotAvailablePanel ─────────────────────────────────────────────────────────
+
+describe("NotAvailablePanel", () => {
+  it("renders heading 'Files not available'", () => {
+    const { container } = render(<NotAvailablePanel runtime="external" />);
+    expect(container.textContent).toContain("Files not available");
+  });
+
+  it("renders the runtime name in monospace", () => {
+    const { container } = render(<NotAvailablePanel runtime="external" />);
+    expect(container.textContent).toContain("external");
+    const spans = container.querySelectorAll("span");
+    const monoSpans = Array.from(spans).filter(
+      (s) => s.className && s.className.includes("font-mono"),
+    );
+    expect(monoSpans.length).toBeGreaterThan(0);
+  });
+
+  it("renders a Chat tab hint in description", () => {
+    const { container } = render(<NotAvailablePanel runtime="remote-agent" />);
+    expect(container.textContent).toContain("Chat tab");
+  });
+
+  it("SVG icon has aria-hidden=true", () => {
+    const { container } = render(<NotAvailablePanel runtime="external" />);
+    const svg = container.querySelector("svg");
+    expect(svg?.getAttribute("aria-hidden")).toBe("true");
+  });
+
+  it("renders without crashing for any runtime string", () => {
+    const { container } = render(<NotAvailablePanel runtime="unknown-runtime" />);
+    expect(container.textContent).toContain("unknown-runtime");
+  });
+
+  it("applies the correct layout classes to root div", () => {
+    const { container } = render(<NotAvailablePanel runtime="external" />);
+    const root = container.firstElementChild as HTMLElement;
+    expect(root.className).toContain("flex");
+    expect(root.className).toContain("flex-col");
+    expect(root.className).toContain("items-center");
+  });
+});
+
+// ─── FilesToolbar ───────────────────────────────────────────────────────────────
+
+describe("FilesToolbar", () => {
+  const noop = vi.fn();
+
+  function renderToolbar(props: Partial<React.ComponentProps<typeof FilesToolbar>> = {}) {
+    return render(
+      <FilesToolbar
+        root="/configs"
+        setRoot={noop}
+        fileCount={0}
+        onNewFile={noop}
+        onUpload={noop}
+        onDownloadAll={noop}
+        onClearAll={noop}
+        onRefresh={noop}
+        {...props}
+      />,
+    );
+  }
+
+  it("renders the directory selector with correct aria-label", () => {
+    const { container } = renderToolbar();
+    const select = container.querySelector("select");
+    expect(select?.getAttribute("aria-label")).toBe("File root directory");
+  });
+
+  it("directory selector has all four options", () => {
+    const { container } = renderToolbar();
+    const select = container.querySelector("select") as HTMLSelectElement;
+    const options = Array.from(select?.options ?? []);
+    const values = options.map((o) => o.value);
+    expect(values).toContain("/configs");
+    expect(values).toContain("/home");
+    expect(values).toContain("/workspace");
+    expect(values).toContain("/plugins");
+  });
+
+  it("calls setRoot when directory changes", () => {
+    const setRoot = vi.fn();
+    const { container } = renderToolbar({ setRoot });
+    const select = container.querySelector("select") as HTMLSelectElement;
+    select.value = "/home";
+    select.dispatchEvent(new Event("change", { bubbles: true }));
+    expect(setRoot).toHaveBeenCalledWith("/home");
+  });
+
+  it("displays the file count", () => {
+    const { container } = renderToolbar({ fileCount: 42 });
+    expect(container.textContent).toContain("42 files");
+  });
+
+  it("shows New + Upload + Clear buttons for /configs", () => {
+    const { container } = renderToolbar({ root: "/configs" });
+    const texts = Array.from(container.querySelectorAll("button")).map(
+      (b) => b.textContent?.trim(),
+    );
+    expect(texts).toContain("+ New");
+    expect(texts).toContain("Upload");
+    expect(texts).toContain("Clear");
+    expect(texts).toContain("Export");
+    expect(texts).toContain("↻");
+  });
+
+  it("hides New + Upload + Clear for /workspace", () => {
+    const { container } = renderToolbar({ root: "/workspace" });
+    const texts = Array.from(container.querySelectorAll("button")).map(
+      (b) => b.textContent?.trim(),
+    );
+    expect(texts).not.toContain("+ New");
+    expect(texts).not.toContain("Upload");
+    expect(texts).not.toContain("Clear");
+    expect(texts).toContain("Export");
+  });
+
+  it("hides New + Upload + Clear for /home", () => {
+    const { container } = renderToolbar({ root: "/home" });
+    const texts = Array.from(container.querySelectorAll("button")).map(
+      (b) => b.textContent?.trim(),
+    );
+    expect(texts).not.toContain("+ New");
+    expect(texts).not.toContain("Upload");
+    expect(texts).not.toContain("Clear");
+  });
+
+  it("hides New + Upload + Clear for /plugins", () => {
+    const { container } = renderToolbar({ root: "/plugins" });
+    const texts = Array.from(container.querySelectorAll("button")).map(
+      (b) => b.textContent?.trim(),
+    );
+    expect(texts).not.toContain("+ New");
+    expect(texts).not.toContain("Upload");
+    expect(texts).not.toContain("Clear");
+  });
+
+  it("New button has correct aria-label", () => {
+    const { container } = renderToolbar({ root: "/configs" });
+    const newBtn = container.querySelector('button[aria-label="Create new file"]');
+    expect(newBtn?.textContent?.trim()).toBe("+ New");
+  });
+
+  it("Export button has correct aria-label", () => {
+    const { container } = renderToolbar();
+    const exportBtn = container.querySelector('button[aria-label="Download all files"]');
+    expect(exportBtn?.textContent?.trim()).toBe("Export");
+  });
+
+  it("Clear button has correct aria-label", () => {
+    const { container } = renderToolbar({ root: "/configs" });
+    const clearBtn = container.querySelector('button[aria-label="Delete all files"]');
+    expect(clearBtn?.textContent?.trim()).toBe("Clear");
+  });
+
+  it("Refresh button has correct aria-label", () => {
+    const { container } = renderToolbar();
+    const refreshBtn = container.querySelector('button[aria-label="Refresh file list"]');
+    expect(refreshBtn?.textContent?.trim()).toBe("↻");
+  });
+
+  it("calls onNewFile when New button is clicked", () => {
+    const onNewFile = vi.fn();
+    const { container } = renderToolbar({ root: "/configs", onNewFile });
+    container.querySelector('button[aria-label="Create new file"]')!.click();
+    expect(onNewFile).toHaveBeenCalledTimes(1);
+  });
+
+  it("calls onDownloadAll when Export button is clicked", () => {
+    const onDownloadAll = vi.fn();
+    const { container } = renderToolbar({ onDownloadAll });
+    container.querySelector('button[aria-label="Download all files"]')!.click();
+    expect(onDownloadAll).toHaveBeenCalledTimes(1);
+  });
+
+  it("calls onClearAll when Clear button is clicked", () => {
+    const onClearAll = vi.fn();
+    const { container } = renderToolbar({ root: "/configs", onClearAll });
+    container.querySelector('button[aria-label="Delete all files"]')!.click();
+    expect(onClearAll).toHaveBeenCalledTimes(1);
+  });
+
+  it("calls onRefresh when Refresh button is clicked", () => {
+    const onRefresh = vi.fn();
+    const { container } = renderToolbar({ onRefresh });
+    container.querySelector('button[aria-label="Refresh file list"]')!.click();
+    expect(onRefresh).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/canvas/src/components/tabs/__tests__/BudgetSection.test.tsx b/canvas/src/components/tabs/__tests__/BudgetSection.test.tsx
new file mode 100644
index 00000000..317703ab
--- /dev/null
+++ b/canvas/src/components/tabs/__tests__/BudgetSection.test.tsx
@@ -0,0 +1,323 @@
+// @vitest-environment jsdom
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { render, screen, cleanup, fireEvent } from "@testing-library/react";
+import React from "react";
+import { BudgetSection } from "../BudgetSection";
+import { api } from "@/lib/api";
+
+// Queue-based mock for the api module. Each api call shifts from the queue.
+// Tests push with qGet/qPatch and the module-level mockImplementation
+// reads from the queue.
+type QueueEntry = { body?: unknown; err?: Error };
+const apiQueue: QueueEntry[] = [];
+
+vi.mock("@/lib/api", () => ({
+  api: {
+    get: vi.fn(async (_path: string) => {
+      const next = apiQueue.shift();
+      if (!next) throw new Error("api.get queue exhausted");
+      if (next.err) throw next.err;
+      return next.body;
+    }),
+    patch: vi.fn(async (_path: string, _body?: unknown) => {
+      const next = apiQueue.shift();
+      if (!next) throw new Error("api.patch queue exhausted");
+      if (next.err) throw next.err;
+      return next.body;
+    }),
+  },
+}));
+
+afterEach(cleanup);
+
+beforeEach(() => {
+  apiQueue.length = 0;
+  vi.clearAllMocks();
+});
+
+const WS_ID = "budget-test-ws";
+
+function qGet(body: unknown) {
+  apiQueue.push({ body });
+}
+
+function qGetErr(status: number, msg: string) {
+  apiQueue.push({ err: new Error(`${msg}: ${status}`) });
+}
+
+function qPatch(body: unknown) {
+  apiQueue.push({ body });
+}
+
+function qPatchErr(status: number, msg: string) {
+  apiQueue.push({ err: new Error(`${msg}: ${status}`) });
+}
+
+function makeBudget(overrides: Partial<{
+  budget_limit: number | null;
+  budget_used: number;
+  budget_remaining: number | null;
+}> = {}) {
+  return {
+    budget_limit: 10_000,
+    budget_used: 3_500,
+    budget_remaining: 6_500,
+    ...overrides,
+  };
+}
+
+describe("BudgetSection", () => {
+  describe("loading state", () => {
+    it("shows loading indicator while fetching", async () => {
+      let resolveGet: (v: unknown) => void;
+      vi.mocked(api.get).mockImplementationOnce(
+        async () => new Promise((r) => { resolveGet = r as (v: unknown) => void; }),
+      );
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      expect(screen.getByTestId("budget-loading")).toBeTruthy();
+
+      resolveGet!(makeBudget());
+      await vi.waitFor(() => {
+        expect(screen.queryByTestId("budget-loading")).toBeNull();
+      });
+    });
+  });
+
+  describe("fetch error state", () => {
+    it("shows error message on non-402 fetch failure", async () => {
+      qGetErr(500, "Internal Server Error");
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-fetch-error")).toBeTruthy();
+      });
+      expect(screen.getByTestId("budget-fetch-error")!.textContent).toContain("500");
+    });
+
+    it("shows 402 as exceeded banner, not fetch error", async () => {
+      qGetErr(402, "Payment Required");
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-exceeded-banner")).toBeTruthy();
+      });
+      expect(screen.queryByTestId("budget-fetch-error")).toBeNull();
+    });
+  });
+
+  describe("budget loaded — display", () => {
+    it("renders used / limit stats row", async () => {
+      qGet(makeBudget({ budget_limit: 10_000, budget_used: 3_500 }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-used-value")!.textContent).toBe("3,500");
+      });
+      expect(screen.getByTestId("budget-limit-value")!.textContent).toBe("10,000");
+    });
+
+    it("renders 'Unlimited' when budget_limit is null", async () => {
+      qGet(makeBudget({ budget_limit: null, budget_used: 1_000, budget_remaining: null }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-limit-value")!.textContent).toBe("Unlimited");
+      });
+    });
+
+    it("renders remaining credits when present", async () => {
+      qGet(makeBudget({ budget_limit: 10_000, budget_used: 3_500, budget_remaining: 6_500 }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-remaining")!.textContent).toContain("6,500");
+        expect(screen.getByTestId("budget-remaining")!.textContent).toContain("credits remaining");
+      });
+    });
+
+    it("omits remaining credits when budget_remaining is null", async () => {
+      qGet(makeBudget({ budget_limit: 10_000, budget_used: 3_500, budget_remaining: null }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.queryByTestId("budget-remaining")).toBeNull();
+      });
+    });
+
+    it("caps progress bar at 100% when used > limit", async () => {
+      qGet(makeBudget({ budget_limit: 10_000, budget_used: 12_000, budget_remaining: null }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        const fill = screen.getByTestId("budget-progress-fill");
+        expect(fill.getAttribute("style")).toContain("100%");
+      });
+    });
+
+    it("omits progress bar when budget_limit is null (unlimited)", async () => {
+      qGet(makeBudget({ budget_limit: null, budget_used: 5_000, budget_remaining: null }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.queryByTestId("budget-progress-fill")).toBeNull();
+      });
+    });
+  });
+
+  describe("budget exceeded (402)", () => {
+    it("shows exceeded banner when load returns 402", async () => {
+      qGetErr(402, "Payment Required");
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-exceeded-banner")).toBeTruthy();
+        expect(screen.getByTestId("budget-exceeded-banner")!.textContent).toContain("Budget exceeded");
+      });
+    });
+
+    it("clears exceeded banner after successful save", async () => {
+      qGetErr(402, "Payment Required");
+      qPatch(makeBudget({ budget_limit: 50_000, budget_used: 0, budget_remaining: 50_000 }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-exceeded-banner")).toBeTruthy();
+      });
+
+      const input = screen.getByTestId("budget-limit-input");
+      fireEvent.change(input, { target: { value: "50000" } });
+
+      const saveBtn = screen.getByTestId("budget-save-btn");
+      fireEvent.click(saveBtn);
+
+      await vi.waitFor(() => {
+        expect(screen.queryByTestId("budget-exceeded-banner")).toBeNull();
+      });
+    });
+  });
+
+  describe("save flow", () => {
+    it("shows save error on non-402 patch failure", async () => {
+      qGet(makeBudget());
+      qPatchErr(500, "Internal Server Error");
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-limit-input")).toBeTruthy();
+      });
+
+      const saveBtn = screen.getByTestId("budget-save-btn");
+      fireEvent.click(saveBtn);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-save-error")).toBeTruthy();
+        expect(screen.getByTestId("budget-save-error")!.textContent).toContain("500");
+      });
+    });
+
+    it("updates input to new limit value after successful save", async () => {
+      qGet(makeBudget({ budget_limit: 10_000 }));
+      qPatch(makeBudget({ budget_limit: 20_000 }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.queryByTestId("budget-loading")).toBeNull();
+      });
+
+      const input = screen.getByTestId("budget-limit-input") as HTMLInputElement;
+      expect(input.value).toBe("10000");
+      expect(screen.getByTestId("budget-limit-value")!.textContent).toBe("10,000");
+
+      fireEvent.change(input, { target: { value: "20000" } });
+      expect(input.value).toBe("20000");
+
+      fireEvent.click(screen.getByTestId("budget-save-btn"));
+
+      await vi.waitFor(() => {
+        expect((screen.getByTestId("budget-limit-input") as HTMLInputElement).value).toBe("20000");
+      });
+    });
+
+    it("sends null when input is cleared (unlimited)", async () => {
+      qGet(makeBudget({ budget_limit: 10_000 }));
+      qPatch(makeBudget({ budget_limit: null }));
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-limit-input")).toBeTruthy();
+      });
+
+      const input = screen.getByTestId("budget-limit-input") as HTMLInputElement;
+      fireEvent.change(input, { target: { value: "" } });
+      fireEvent.click(screen.getByTestId("budget-save-btn"));
+
+      await vi.waitFor(() => {
+        expect(input.value).toBe("");
+      });
+    });
+
+    it("shows saving state on button while patch is in flight", async () => {
+      qGet(makeBudget());
+      let resolvePatch: (v: unknown) => void;
+      vi.mocked(api.patch).mockImplementationOnce(
+        async () => new Promise((r) => { resolvePatch = r as (v: unknown) => void; }),
+      );
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-limit-input")).toBeTruthy();
+      });
+
+      fireEvent.change(screen.getByTestId("budget-limit-input"), { target: { value: "50000" } });
+      fireEvent.click(screen.getByTestId("budget-save-btn"));
+
+      const btn = screen.getByTestId("budget-save-btn");
+      expect(btn.textContent).toContain("Saving");
+
+      resolvePatch!(makeBudget({ budget_limit: 50_000 }));
+      await vi.waitFor(() => {
+        expect(btn.textContent).toContain("Save");
+      });
+    });
+  });
+
+  describe("isApiError402 — regression coverage", () => {
+    it("classifies ': 402' with space as 402", async () => {
+      qGetErr(402, "Payment Required");
+      qPatch(makeBudget());
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-exceeded-banner")).toBeTruthy();
+      });
+    });
+
+    it("classifies non-402 error messages as regular fetch errors", async () => {
+      qGetErr(503, "Service Unavailable");
+
+      render(<BudgetSection workspaceId={WS_ID} />);
+
+      await vi.waitFor(() => {
+        expect(screen.getByTestId("budget-fetch-error")).toBeTruthy();
+      });
+      expect(screen.queryByTestId("budget-exceeded-banner")).toBeNull();
+    });
+  });
+});