diff --git a/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx b/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx
index 46e57874..5ac054a9 100644
--- a/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx
+++ b/canvas/src/components/tabs/FilesTab/__tests__/FilesTab.test.tsx
@@ -1,216 +1,162 @@
 // @vitest-environment jsdom
 /**
- * FilesTab: NotAvailablePanel + FilesToolbar coverage.
+ * Tests for the main FilesTab / PlatformOwnedFilesTab component.
  *
- * 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.
+ * Covers: NotAvailablePanel (external runtime), loading/empty/error states,
+ * FilesToolbar actions, and the /configs-only upload guard.
  *
- * No @testing-library/jest-dom import — use textContent / className /
- * getAttribute checks to avoid "expect is not defined" errors.
+ * No @testing-library/jest-dom — use textContent / className / getAttribute.
  */
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { cleanup, render, screen } from "@testing-library/react";
+import { cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
 import React from "react";
 
-import { FilesToolbar } from "../FilesToolbar";
-import { NotAvailablePanel } from "../NotAvailablePanel";
+import { FilesTab } from "../../FilesTab.tsx";
+import type { FileEntry } from "../../FilesTab/tree";
 
-// ─── afterEach ─────────────────────────────────────────────────────────────────
+// ─── Mock ──────────────────────────────────────────────────────────────────
+
+const _mockGet = vi.hoisted(() => vi.fn<() => Promise<unknown>>());
+vi.mock("@/lib/api", () => ({
+  api: { get: _mockGet, put: vi.fn(), del: vi.fn() },
+}));
 
 afterEach(() => {
   cleanup();
-  vi.restoreAllMocks();
+  _mockGet.mockReset();
 });
 
-// ─── NotAvailablePanel ─────────────────────────────────────────────────────────
+// ─── Helpers ───────────────────────────────────────────────────────────────
 
-describe("NotAvailablePanel", () => {
-  it("renders heading 'Files not available'", () => {
-    const { container } = render(<NotAvailablePanel runtime="external" />);
-    expect(container.textContent).toContain("Files not available");
-  });
+const emptyFileList: FileEntry[] = [];
 
-  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);
-  });
+/** Render FilesTab with a non-external runtime (triggers PlatformOwnedFilesTab). */
+function renderPlatformTab(extraProps: Partial<React.ComponentProps<typeof FilesTab>> = {}) {
+  return render(
+    <FilesTab
+      workspaceId="ws-1"
+      data={{ id: "ws-1", name: "Test", runtime: "claude-code", status: "online", tier: 0, skills: [], created_at: "" }}
+      {...extraProps}
+    />,
+  );
+}
 
-  it("renders a Chat tab hint in description", () => {
-    const { container } = render(<NotAvailablePanel runtime="remote-agent" />);
-    expect(container.textContent).toContain("Chat tab");
-  });
+// ─── NotAvailablePanel ──────────────────────────────────────────────────────
 
-  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}
+describe("FilesTab — NotAvailablePanel", () => {
+  it("renders NotAvailablePanel when runtime is external", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    render(
+      <FilesTab
+        workspaceId="ws-1"
+        data={{ id: "ws-1", name: "Test", runtime: "external", status: "online", tier: 0, skills: [], created_at: "" }}
       />,
     );
-  }
-
-  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");
+    expect(screen.getByText(/Files not available/i)).toBeTruthy();
   });
 
-  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(),
+  it("renders the runtime name in NotAvailablePanel", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    render(
+      <FilesTab
+        workspaceId="ws-1"
+        data={{ id: "ws-1", name: "Test", runtime: "external", status: "online", tier: 0, skills: [], created_at: "" }}
+      />,
     );
-    expect(texts).toContain("+ New");
-    expect(texts).toContain("Upload");
-    expect(texts).toContain("Clear");
-    expect(texts).toContain("Export");
-    expect(texts).toContain("↻");
+    expect(screen.getByText(/external/i)).toBeTruthy();
   });
 
-  it("hides New + Upload + Clear for /workspace", () => {
-    const { container } = renderToolbar({ root: "/workspace" });
-    const texts = Array.from(container.querySelectorAll("button")).map(
-      (b) => b.textContent?.trim(),
+  it("does NOT call api.get when runtime is external", async () => {
+    render(
+      <FilesTab
+        workspaceId="ws-1"
+        data={{ id: "ws-1", name: "Test", runtime: "external", status: "online", tier: 0, skills: [], created_at: "" }}
+      />,
     );
-    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);
+    expect(_mockGet).not.toHaveBeenCalled();
+  });
+});
+
+// ─── Loading / Empty / Error states ────────────────────────────────────────
+
+describe("FilesTab — states", () => {
+  it("shows loading text while fetching files", () => {
+    _mockGet.mockImplementation(
+      () => new Promise<unknown>(() => {}) as unknown as Promise<unknown>,
+    );
+    renderPlatformTab();
+    expect(screen.getByText("Loading files...")).toBeTruthy();
+  });
+
+  it("shows 'No config files yet' when root is /configs and no files", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => {
+      expect(screen.getByText(/No config files yet/i)).toBeTruthy();
+    });
+  });
+
+  it("fetches from the correct endpoint", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => {
+      expect(_mockGet).toHaveBeenCalledWith(expect.stringContaining("/workspaces/ws-1/files"));
+    });
+  });
+
+  it("shows file count from toolbar when files exist", async () => {
+    _mockGet.mockResolvedValue([
+      { path: "configs/a.yaml", size: 10, dir: false },
+      { path: "configs/b.yaml", size: 20, dir: false },
+    ]);
+    renderPlatformTab();
+    await waitFor(() => {
+      expect(screen.getByText("2 files")).toBeTruthy();
+    });
+  });
+});
+
+// ─── FilesToolbar ──────────────────────────────────────────────────────────
+
+describe("FilesTab — FilesToolbar", () => {
+  it("shows Refresh button", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => {
+      expect(screen.getByLabelText("Refresh file list")).toBeTruthy();
+    });
+  });
+
+  it("shows root directory selector", async () => {
+    _mockGet.mockResolvedValueOnce(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => {
+      expect(screen.getByRole("combobox")).toBeTruthy();
+    });
+  });
+
+  it("Refresh button triggers a reload", async () => {
+    // Use persistent mock — loadFiles fires on mount AND on Refresh click.
+    _mockGet.mockResolvedValue(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => screen.getByLabelText("Refresh file list"));
+    const before = _mockGet.mock.calls.length;
+    fireEvent.click(screen.getByLabelText("Refresh file list"));
+    await waitFor(() => {
+      expect(_mockGet.mock.calls.length).toBeGreaterThan(before);
+    });
+  });
+});
+
+// ─── Upload guard ──────────────────────────────────────────────────────────
+
+describe("FilesTab — upload guard", () => {
+  it("no error alert on dragover when root is /configs (default)", async () => {
+    _mockGet.mockResolvedValue(emptyFileList);
+    renderPlatformTab();
+    await waitFor(() => screen.getByText(/No config files yet/i));
+
+    // No alert should be present
+    expect(screen.queryByRole("alert")).toBeNull();
   });
 });
diff --git a/canvas/src/components/tabs/FilesTab/__tests__/tree.test.ts b/canvas/src/components/tabs/FilesTab/__tests__/tree.test.ts
new file mode 100644
index 00000000..4ba9f594
--- /dev/null
+++ b/canvas/src/components/tabs/FilesTab/__tests__/tree.test.ts
@@ -0,0 +1,218 @@
+// @vitest-environment jsdom
+/**
+ * Tests for tree.ts — buildTree and getIcon pure functions.
+ */
+import { describe, expect, it } from "vitest";
+import type { FileEntry } from "../tree";
+import { buildTree, getIcon } from "../tree";
+
+// ─── getIcon ─────────────────────────────────────────────────────────────────
+
+describe("getIcon", () => {
+  it("returns folder emoji for directories", () => {
+    expect(getIcon("/configs", true)).toBe("📁");
+  });
+
+  it("returns correct emoji for .md", () => {
+    expect(getIcon("readme.md", false)).toBe("📄");
+  });
+
+  it("returns correct emoji for .yaml", () => {
+    expect(getIcon("config.yaml", false)).toBe("⚙");
+  });
+
+  it("returns correct emoji for .yml", () => {
+    expect(getIcon("config.yml", false)).toBe("⚙");
+  });
+
+  it("returns correct emoji for .py", () => {
+    expect(getIcon("script.py", false)).toBe("🐍");
+  });
+
+  it("returns correct emoji for .ts", () => {
+    expect(getIcon("index.ts", false)).toBe("💠");
+  });
+
+  it("returns correct emoji for .tsx", () => {
+    expect(getIcon("App.tsx", false)).toBe("💠");
+  });
+
+  it("returns correct emoji for .js", () => {
+    expect(getIcon("index.js", false)).toBe("📜");
+  });
+
+  it("returns correct emoji for .json", () => {
+    expect(getIcon("package.json", false)).toBe("{}");
+  });
+
+  it("returns correct emoji for .html", () => {
+    expect(getIcon("index.html", false)).toBe("🌐");
+  });
+
+  it("returns correct emoji for .css", () => {
+    expect(getIcon("style.css", false)).toBe("🎨");
+  });
+
+  it("returns correct emoji for .sh", () => {
+    expect(getIcon("deploy.sh", false)).toBe("▸");
+  });
+
+  it("returns default file emoji for unknown extensions", () => {
+    expect(getIcon("Makefile", false)).toBe("📄");
+    expect(getIcon("Dockerfile", false)).toBe("📄");
+    expect(getIcon("Rakefile", false)).toBe("📄");
+  });
+
+  it("extension matching is case-insensitive", () => {
+    expect(getIcon("readme.MD", false)).toBe("📄");
+    expect(getIcon("script.PY", false)).toBe("🐍");
+  });
+});
+
+// ─── buildTree ───────────────────────────────────────────────────────────────
+
+describe("buildTree", () => {
+  it("returns empty array for empty input", () => {
+    expect(buildTree([])).toEqual([]);
+  });
+
+  it("adds a single file at root", () => {
+    const files: FileEntry[] = [{ path: "config.yaml", size: 128, dir: false }];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(1);
+    expect(tree[0]).toMatchObject({
+      name: "config.yaml",
+      path: "config.yaml",
+      isDir: false,
+      children: [],
+      size: 128,
+    });
+  });
+
+  it("adds a single directory at root", () => {
+    const files: FileEntry[] = [{ path: "skills", size: 0, dir: true }];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(1);
+    expect(tree[0]).toMatchObject({
+      name: "skills",
+      path: "skills",
+      isDir: true,
+      children: [],
+      size: 0,
+    });
+  });
+
+  it("sorts dirs before files at the same level", () => {
+    const files: FileEntry[] = [
+      { path: "b.txt", size: 10, dir: false },
+      { path: "a.txt", size: 10, dir: false },
+      { path: "z-dir", size: 0, dir: true },
+      { path: "a-dir", size: 0, dir: true },
+    ];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(4);
+    // Dirs first: z-dir, a-dir alphabetically → a before z
+    expect(tree[0].name).toBe("a-dir");
+    expect(tree[1].name).toBe("z-dir");
+    // Then files alphabetically
+    expect(tree[2].name).toBe("a.txt");
+    expect(tree[3].name).toBe("b.txt");
+  });
+
+  it("alphabetically sorts files within the same level", () => {
+    const files: FileEntry[] = [
+      { path: "z.yaml", size: 10, dir: false },
+      { path: "a.yaml", size: 10, dir: false },
+      { path: "m.yaml", size: 10, dir: false },
+    ];
+    const tree = buildTree(files);
+    expect(tree.map((n) => n.name)).toEqual(["a.yaml", "m.yaml", "z.yaml"]);
+  });
+
+  it("nests a file under its parent directory", () => {
+    const files: FileEntry[] = [
+      { path: "skills", size: 0, dir: true },
+      { path: "skills/readme.md", size: 64, dir: false },
+    ];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(1);
+    expect(tree[0].name).toBe("skills");
+    expect(tree[0].children).toHaveLength(1);
+    expect(tree[0].children[0]).toMatchObject({
+      name: "readme.md",
+      path: "skills/readme.md",
+      isDir: false,
+      size: 64,
+    });
+  });
+
+  it("creates intermediate directories automatically", () => {
+    const files: FileEntry[] = [
+      { path: "a/b/c/deep.txt", size: 32, dir: false },
+    ];
+    const tree = buildTree(files);
+    // Root has one child: "a"
+    expect(tree).toHaveLength(1);
+    expect(tree[0].name).toBe("a");
+    expect(tree[0].isDir).toBe(true);
+    // "a" has one child: "b"
+    expect(tree[0].children).toHaveLength(1);
+    expect(tree[0].children[0].name).toBe("b");
+    // "b" has one child: "c"
+    expect(tree[0].children[0].children).toHaveLength(1);
+    expect(tree[0].children[0].children[0].name).toBe("c");
+    // "c" has the file
+    expect(tree[0].children[0].children[0].children[0].name).toBe("deep.txt");
+    expect(tree[0].children[0].children[0].children[0].size).toBe(32);
+  });
+
+  it("adds multiple files to the same directory", () => {
+    const files: FileEntry[] = [
+      { path: "configs", size: 0, dir: true },
+      { path: "configs/a.yaml", size: 10, dir: false },
+      { path: "configs/b.yaml", size: 20, dir: false },
+    ];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(1);
+    expect(tree[0].children.map((n) => n.name).sort()).toEqual(["a.yaml", "b.yaml"]);
+  });
+
+  it("does not duplicate a directory already created as intermediate", () => {
+    const files: FileEntry[] = [
+      { path: "a/b.txt", size: 5, dir: false },
+      { path: "a", size: 0, dir: true },
+    ];
+    const tree = buildTree(files);
+    // "a" should appear only once
+    expect(tree).toHaveLength(1);
+    expect(tree[0].name).toBe("a");
+    // The dir "a" should still contain "b.txt"
+    expect(tree[0].children).toHaveLength(1);
+    expect(tree[0].children[0].name).toBe("b.txt");
+  });
+
+  it("intermediate dirs have size 0", () => {
+    const files: FileEntry[] = [
+      { path: "a/b/c/file.txt", size: 1, dir: false },
+    ];
+    const tree = buildTree(files);
+    expect(tree[0].size).toBe(0);
+    expect(tree[0].children[0].size).toBe(0);
+  });
+
+  it("handles deeply nested mixed dirs and files", () => {
+    const files: FileEntry[] = [
+      { path: "a", size: 0, dir: true },
+      { path: "a/b", size: 0, dir: true },
+      { path: "a/b/c", size: 0, dir: true },
+      { path: "a/b/c/d.txt", size: 1, dir: false },
+      { path: "a/b/e.txt", size: 2, dir: false },
+      { path: "a/f.txt", size: 3, dir: false },
+    ];
+    const tree = buildTree(files);
+    expect(tree).toHaveLength(1); // root: "a"
+    expect(tree[0].children.map((n) => n.name).sort()).toEqual(["b", "f.txt"]);
+    expect(tree[0].children.find((n) => n.name === "b")!.children.map((n) => n.name).sort())
+      .toEqual(["c", "e.txt"]);
+  });
+});