diff --git a/frontend/components/chat/artifacts-rail.test.tsx b/frontend/components/chat/artifacts-rail.test.tsx
new file mode 100644
index 00000000..0bbe2939
--- /dev/null
+++ b/frontend/components/chat/artifacts-rail.test.tsx
@@ -0,0 +1,157 @@
+// Two halves. First, static-markup tests of ArtifactsRailView, the presentational
+// half that takes the rail's state as props: the loading, empty, unavailable and
+// list states each render their own copy, and the refresh icon spins only when the
+// `refreshing` prop is set. Second, an interaction test that mounts the real
+// ArtifactsRail container and proves the spinner rule end to end: the initial load
+// and the 5-second poll share one non-manual code path that never spins the icon,
+// while a viewer's click does.
+//
+// The container test drives the rail through local `fetch`/`EventSource` stubs
+// restored in a finally, rather than bun's mock.module: mock.module is
+// process-wide and would leak a never-resolving backendFetch into every test
+// file loaded after this one, hanging unrelated component tests.
+import { expect, test } from "bun:test";
+import { GlobalRegistrator } from "@happy-dom/global-registrator";
+import { renderToStaticMarkup } from "react-dom/server";
+import type { ArtifactDescriptor } from "@/components/artifacts/model";
+import { ArtifactsRail, ArtifactsRailView } from "./artifacts-rail";
+
+if (typeof window === "undefined") GlobalRegistrator.register();
+
+const { act } = await import("react");
+const { createRoot } = await import("react-dom/client");
+
+const FILE: ArtifactDescriptor = {
+  id: "a1",
+  run_id: "r1",
+  thread_id: "t1",
+  name: "report.docx",
+  source_path: "/root/work/report.docx",
+  content_type: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+  size_bytes: 2048,
+  sha256: "abc123",
+  created_at: "2026-01-01T00:00:00Z",
+  preview_url: "https://example.com/preview",
+  download_url: "https://example.com/download",
+  preview_pdf_url: null,
+  workpiece: null,
+};
+
+const noop = () => {};
+
+test("the loading state shows while the backend has not answered yet", () => {
+  const html = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[]} available={null} refreshing={false} onRefresh={noop} />,
+  );
+  expect(html).toContain("Loading files...");
+  expect(html).not.toContain("No files yet");
+  expect(html).not.toContain("Files unavailable");
+});
+
+test("the empty state shows once the backend answers with no files", () => {
+  const html = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[]} available={true} refreshing={false} onRefresh={noop} />,
+  );
+  expect(html).toContain("No files yet");
+  expect(html).not.toContain("Loading files...");
+});
+
+test("the unavailable state shows when the backend request failed", () => {
+  const html = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[]} available={false} refreshing={false} onRefresh={noop} />,
+  );
+  expect(html).toContain("Files unavailable");
+  expect(html).toContain("Refresh to reconnect.");
+});
+
+test("the list state renders a card per file and no placeholder", () => {
+  const html = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[FILE]} available={true} refreshing={false} onRefresh={noop} />,
+  );
+  expect(html).toContain("report.docx");
+  expect(html).not.toContain("No files yet");
+  expect(html).not.toContain("Files unavailable");
+});
+
+test("the refresh icon spins and the button disables only when refreshing is set", () => {
+  const spinning = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[]} available={true} refreshing={true} onRefresh={noop} />,
+  );
+  expect(spinning).toContain("animate-spin");
+  expect(spinning).toContain("disabled");
+
+  const still = renderToStaticMarkup(
+    <ArtifactsRailView artifacts={[]} available={true} refreshing={false} onRefresh={noop} />,
+  );
+  expect(still).not.toContain("animate-spin");
+});
+
+test("a background load never spins the icon; a manual click does", async () => {
+  const originalFetch = globalThis.fetch;
+  const originalEventSource = (globalThis as { EventSource?: unknown }).EventSource;
+  // happy-dom has no EventSource; the rail's org-change subscription opens one.
+  (globalThis as { EventSource?: unknown }).EventSource = class {
+    close() {}
+    addEventListener() {}
+    removeEventListener() {}
+  };
+  // Hand out responses on demand so we can inspect the in-flight state.
+  const resolvers: Array<(body: unknown) => void> = [];
+  globalThis.fetch = (() =>
+    new Promise<Response>((resolve) => {
+      resolvers.push((body) =>
+        resolve({
+          ok: true,
+          status: 200,
+          headers: new Headers(),
+          json: async () => body,
+        } as unknown as Response),
+      );
+    })) as unknown as typeof fetch;
+
+  const host = document.createElement("div");
+  document.body.appendChild(host);
+  const root = createRoot(host);
+  try {
+    // Mount: the initial load fires on the same non-manual path the 5-second
+    // poll uses. Its request is in flight and must not spin the control.
+    await act(async () => {
+      root.render(<ArtifactsRail threadId="t1" live={true} />);
+    });
+    const button = host.querySelector<HTMLButtonElement>(
+      'button[aria-label="Refresh session files"]',
+    );
+    if (!button) throw new Error("refresh button not found");
+    expect(resolvers.length).toBe(1); // the initial (non-manual) load is pending
+    expect(button.querySelector(".animate-spin")).toBeNull();
+    expect(button.disabled).toBe(false);
+
+    // Finish the initial load with an empty list.
+    await act(async () => {
+      resolvers.shift()?.({ artifacts: [] });
+    });
+    expect(button.querySelector(".animate-spin")).toBeNull();
+
+    // A viewer's click starts a manual load: now the icon spins and the button
+    // locks until the request settles.
+    await act(async () => {
+      button.click();
+    });
+    expect(resolvers.length).toBe(1);
+    expect(button.querySelector(".animate-spin")).not.toBeNull();
+    expect(button.disabled).toBe(true);
+
+    await act(async () => {
+      resolvers.shift()?.({ artifacts: [] });
+    });
+    expect(button.querySelector(".animate-spin")).toBeNull();
+    expect(button.disabled).toBe(false);
+  } finally {
+    await act(async () => {
+      root.unmount();
+    });
+    host.remove();
+    globalThis.fetch = originalFetch;
+    (globalThis as { EventSource?: unknown }).EventSource = originalEventSource;
+  }
+});
diff --git a/frontend/components/chat/artifacts-rail.tsx b/frontend/components/chat/artifacts-rail.tsx
index 643d6e75..9e7d36e9 100644
--- a/frontend/components/chat/artifacts-rail.tsx
+++ b/frontend/components/chat/artifacts-rail.tsx
@@ -23,54 +23,22 @@ function SpinningRefreshIcon({
   return <RiRefreshLine {...props} className={cx("animate-spin", className)} />;
 }
 
-export function ArtifactsRail({
-  threadId,
-  live,
+/** The Files rail, driven entirely by its props: the list, whether the backend
+ * answered at all, and whether a manual refresh is in flight. `refreshing` is
+ * the viewer's own click only; the background poll never sets it, so the icon
+ * spins when they ask for a refresh and stays still while a task streams in
+ * new files on its own. */
+export function ArtifactsRailView({
+  artifacts,
+  available,
+  refreshing,
+  onRefresh,
 }: {
-  readonly threadId: string;
-  readonly live: boolean;
+  readonly artifacts: readonly ArtifactDescriptor[];
+  readonly available: boolean | null;
+  readonly refreshing: boolean;
+  readonly onRefresh: () => void;
 }) {
-  const [artifacts, setArtifacts] = useState<ArtifactDescriptor[]>([]);
-  const [available, setAvailable] = useState<boolean | null>(null);
-  const [refreshing, setRefreshing] = useState(false);
-
-  const load = useCallback(
-    async (signal?: AbortSignal) => {
-      setRefreshing(true);
-      try {
-        const response = await backendFetch(artifactQueryForThread(threadId), {
-          cache: "no-store",
-          signal,
-        });
-        if (!response.ok) throw new Error(`artifact request failed (${response.status})`);
-        const parsed = extractArtifacts(await response.json());
-        if (!parsed) throw new Error("artifact response was invalid");
-        setArtifacts(parsed);
-        setAvailable(true);
-      } catch {
-        if (!signal?.aborted) setAvailable(false);
-      } finally {
-        if (!signal?.aborted) setRefreshing(false);
-      }
-    },
-    [threadId],
-  );
-
-  useOrgChanges((change) => {
-    if (change.type === "artifact" && change.threadId === threadId) void load();
-  });
-
-  useEffect(() => {
-    const controller = new AbortController();
-    void load(controller.signal);
-    if (!live) return () => controller.abort();
-    const interval = setInterval(() => void load(controller.signal), LIVE_REFRESH_MS);
-    return () => {
-      controller.abort();
-      clearInterval(interval);
-    };
-  }, [live, load]);
-
   return (
     <div className="absolute inset-0 overflow-y-auto p-3">
       <div className="mb-3 flex items-center justify-between gap-3">
@@ -83,7 +51,7 @@ export function ArtifactsRail({
         <IconButton
           size="small"
           icon={refreshing ? SpinningRefreshIcon : RiRefreshLine}
-          onClick={() => void load()}
+          onClick={onRefresh}
           disabled={refreshing}
           aria-label="Refresh session files"
           title="Refresh"
@@ -117,3 +85,63 @@ export function ArtifactsRail({
     </div>
   );
 }
+
+export function ArtifactsRail({
+  threadId,
+  live,
+}: {
+  readonly threadId: string;
+  readonly live: boolean;
+}) {
+  const [artifacts, setArtifacts] = useState<ArtifactDescriptor[]>([]);
+  const [available, setAvailable] = useState<boolean | null>(null);
+  const [refreshing, setRefreshing] = useState(false);
+
+  const load = useCallback(
+    async ({ manual = false, signal }: { manual?: boolean; signal?: AbortSignal } = {}) => {
+      // Only a viewer's click spins the icon; the 5-second poll and org-change
+      // reloads refresh quietly so the control is not in constant motion.
+      if (manual) setRefreshing(true);
+      try {
+        const response = await backendFetch(artifactQueryForThread(threadId), {
+          cache: "no-store",
+          signal,
+        });
+        if (!response.ok) throw new Error(`artifact request failed (${response.status})`);
+        const parsed = extractArtifacts(await response.json());
+        if (!parsed) throw new Error("artifact response was invalid");
+        setArtifacts(parsed);
+        setAvailable(true);
+      } catch {
+        if (!signal?.aborted) setAvailable(false);
+      } finally {
+        if (manual) setRefreshing(false);
+      }
+    },
+    [threadId],
+  );
+
+  useOrgChanges((change) => {
+    if (change.type === "artifact" && change.threadId === threadId) void load();
+  });
+
+  useEffect(() => {
+    const controller = new AbortController();
+    void load({ signal: controller.signal });
+    if (!live) return () => controller.abort();
+    const interval = setInterval(() => void load({ signal: controller.signal }), LIVE_REFRESH_MS);
+    return () => {
+      controller.abort();
+      clearInterval(interval);
+    };
+  }, [live, load]);
+
+  return (
+    <ArtifactsRailView
+      artifacts={artifacts}
+      available={available}
+      refreshing={refreshing}
+      onRefresh={() => void load({ manual: true })}
+    />
+  );
+}