diff --git a/packages/views/editor/extensions/file-card.test.tsx b/packages/views/editor/extensions/file-card.test.tsx
new file mode 100644
index 000000000..7d0ab9904
--- /dev/null
+++ b/packages/views/editor/extensions/file-card.test.tsx
@@ -0,0 +1,105 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import type { ReactElement } from "react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+// Tiptap NodeView primitives can't be instantiated without a full editor.
+// Stub the wrapper so FileCardView renders as a plain React component and
+// the DOM can be inspected directly.
+vi.mock("@tiptap/react", () => ({
+  NodeViewWrapper: ({ children, ...rest }: any) => <div {...rest}>{children}</div>,
+}));
+
+const { getAttachmentTextContentMock, resolveAttachmentMock, openByUrlMock, tryOpenMock } =
+  vi.hoisted(() => ({
+    getAttachmentTextContentMock: vi.fn(),
+    resolveAttachmentMock: vi.fn(),
+    openByUrlMock: vi.fn(),
+    tryOpenMock: vi.fn(),
+  }));
+
+vi.mock("@multica/core/api", () => ({
+  api: { getAttachmentTextContent: getAttachmentTextContentMock },
+  PreviewTooLargeError: class extends Error {},
+  PreviewUnsupportedError: class extends Error {},
+}));
+
+vi.mock("../attachment-download-context", () => ({
+  useAttachmentDownloadResolver: () => ({
+    openByUrl: openByUrlMock,
+    resolveAttachment: resolveAttachmentMock,
+  }),
+}));
+
+vi.mock("../attachment-preview-modal", () => ({
+  useAttachmentPreview: () => ({ tryOpen: tryOpenMock, open: vi.fn(), modal: null }),
+}));
+
+vi.mock("../i18n", () => ({
+  useT: () => ({
+    t: (sel: (s: Record<string, Record<string, string>>) => string) =>
+      sel({
+        image: { download: "Download" },
+        attachment: {
+          preview: "Preview",
+          preview_loading: "Loading preview…",
+          preview_failed: "Couldn't load preview",
+        },
+        code_block: { copy_code: "Copy code" },
+        file_card: { uploading: "Uploading {{filename}}" },
+      }),
+  }),
+}));
+
+import { FileCardView } from "./file-card";
+
+function renderWithQuery(ui: ReactElement) {
+  const qc = new QueryClient({
+    defaultOptions: { queries: { retry: false, gcTime: 0 } },
+  });
+  return render(<QueryClientProvider client={qc}>{ui}</QueryClientProvider>);
+}
+
+beforeEach(() => vi.clearAllMocks());
+afterEach(() => vi.restoreAllMocks());
+
+describe("FileCardView — HTML attachment routes through AttachmentBlock to iframe", () => {
+  // Regression pin for file-card.tsx:59. The NodeView must render through
+  // <AttachmentBlock>, not the older <AttachmentCard>. If someone reverts that
+  // line, the dispatcher's html+attachmentId branch is bypassed and the user
+  // is left with the file-card chrome — exactly the bug MUL-2330 surfaced.
+  it("renders an iframe (no file-card chrome) when the node resolves to an HTML attachment", async () => {
+    resolveAttachmentMock.mockReturnValue({
+      id: "att-1",
+      content_type: "text/html",
+      url: "/uploads/report.html",
+      filename: "report.html",
+    });
+    getAttachmentTextContentMock.mockResolvedValueOnce({
+      text: "<p>chart</p>",
+      originalContentType: "text/html",
+    });
+
+    const node = {
+      attrs: {
+        href: "/uploads/report.html",
+        filename: "report.html",
+        uploading: false,
+      },
+    } as any;
+
+    renderWithQuery(<FileCardView node={node} {...({} as any)} />);
+
+    const frame = await waitFor(() => {
+      const f = document.querySelector("iframe") as HTMLIFrameElement | null;
+      expect(f).toBeTruthy();
+      return f!;
+    });
+    expect(frame.getAttribute("sandbox")).toBe("allow-scripts");
+    expect(frame.getAttribute("srcdoc")).toContain("<p>chart</p>");
+    // The AttachmentCard chrome surfaces the filename as text inside its row.
+    // HtmlAttachmentPreview replaces the chrome entirely, so the filename
+    // must not appear as visible text.
+    expect(screen.queryByText("report.html")).toBeNull();
+  });
+});
diff --git a/packages/views/editor/extensions/file-card.tsx b/packages/views/editor/extensions/file-card.tsx
index cb42b5207..fe7285a5e 100644
--- a/packages/views/editor/extensions/file-card.tsx
+++ b/packages/views/editor/extensions/file-card.tsx
@@ -31,7 +31,7 @@ const FILE_CARD_MARKDOWN_RE = new RegExp(
 // React NodeView
 // ---------------------------------------------------------------------------
 
-function FileCardView({ node }: NodeViewProps) {
+export function FileCardView({ node }: NodeViewProps) {
   const href = (node.attrs.href as string) || "";
   const filename = (node.attrs.filename as string) || "";
   const uploading = node.attrs.uploading as boolean;
diff --git a/packages/views/editor/readonly-content.test.tsx b/packages/views/editor/readonly-content.test.tsx
index c87948b6e..9e30b6085 100644
--- a/packages/views/editor/readonly-content.test.tsx
+++ b/packages/views/editor/readonly-content.test.tsx
@@ -1,5 +1,17 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { fireEvent, render, waitFor } from "@testing-library/react";
+import type { ReactElement } from "react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+const { getAttachmentTextContentMock } = vi.hoisted(() => ({
+  getAttachmentTextContentMock: vi.fn(),
+}));
+
+vi.mock("@multica/core/api", () => ({
+  api: { getAttachmentTextContent: getAttachmentTextContentMock },
+  PreviewTooLargeError: class extends Error {},
+  PreviewUnsupportedError: class extends Error {},
+}));
 
 vi.mock("@multica/core/paths", () => ({
   useWorkspacePaths: () => ({
@@ -253,3 +265,47 @@ describe("ReadonlyContent HTML block rendering", () => {
     ).not.toBeNull();
   });
 });
+
+describe("ReadonlyContent file-card → AttachmentBlock HTML routing", () => {
+  // Regression pin for readonly-content.tsx:279. The `div data-type=fileCard`
+  // branch must render through <AttachmentBlock>, not the older
+  // <AttachmentCard>. Reverting that line would skip the html+attachmentId
+  // dispatcher branch and surface the bare file-card chrome (filename row)
+  // instead of the rendered iframe — the exact regression MUL-2330 fixed.
+  function renderWithQuery(ui: ReactElement) {
+    const qc = new QueryClient({
+      defaultOptions: { queries: { retry: false, gcTime: 0 } },
+    });
+    return render(<QueryClientProvider client={qc}>{ui}</QueryClientProvider>);
+  }
+
+  it("renders the !file[](url) HTML attachment as an iframe (no file-card chrome)", async () => {
+    getAttachmentTextContentMock.mockResolvedValueOnce({
+      text: "<p>chart</p>",
+      originalContentType: "text/html",
+    });
+    const attachment = {
+      id: "att-1",
+      url: "/uploads/report.html",
+      filename: "report.html",
+      content_type: "text/html",
+      size_bytes: 0,
+    } as any;
+    const { container, queryByText } = renderWithQuery(
+      <ReadonlyContent
+        content="!file[report.html](/uploads/report.html)"
+        attachments={[attachment]}
+      />,
+    );
+    const frame = await waitFor(() => {
+      const f = container.querySelector<HTMLIFrameElement>("iframe");
+      expect(f).not.toBeNull();
+      return f!;
+    });
+    expect(frame.getAttribute("sandbox")).toBe("allow-scripts");
+    expect(frame.getAttribute("srcdoc")).toContain("<p>chart</p>");
+    // AttachmentCard chrome surfaces the filename as visible text in a
+    // <p class="truncate"> row. HtmlAttachmentPreview replaces it entirely.
+    expect(queryByText("report.html")).toBeNull();
+  });
+});
diff --git a/packages/views/issues/components/comment-card.test.tsx b/packages/views/issues/components/comment-card.test.tsx
new file mode 100644
index 000000000..2a7b93dd9
--- /dev/null
+++ b/packages/views/issues/components/comment-card.test.tsx
@@ -0,0 +1,64 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import type { ReactElement } from "react";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+
+const { getAttachmentTextContentMock } = vi.hoisted(() => ({
+  getAttachmentTextContentMock: vi.fn(),
+}));
+
+vi.mock("@multica/core/api", () => ({
+  api: {
+    getAttachmentTextContent: getAttachmentTextContentMock,
+    getAttachment: vi.fn(),
+  },
+  PreviewTooLargeError: class extends Error {},
+  PreviewUnsupportedError: class extends Error {},
+}));
+
+import { AttachmentList } from "./comment-card";
+
+function renderWithQuery(ui: ReactElement) {
+  const qc = new QueryClient({
+    defaultOptions: { queries: { retry: false, gcTime: 0 } },
+  });
+  return render(<QueryClientProvider client={qc}>{ui}</QueryClientProvider>);
+}
+
+beforeEach(() => vi.clearAllMocks());
+afterEach(() => vi.restoreAllMocks());
+
+describe("AttachmentList — standalone HTML attachment routes through AttachmentBlock", () => {
+  // Regression pin for comment-card.tsx:152. This is the entry point
+  // MUL-2330 originally regressed on: standalone HTML attachments (not
+  // referenced inline in the markdown body) MUST render through
+  // <AttachmentBlock> so the html+attachmentId dispatch fires. Reverting to
+  // <AttachmentCard> here re-introduces the "report.html shows as a bare
+  // file card row instead of the rendered chart" bug.
+  it("renders an iframe (no file-card chrome) for a standalone HTML attachment", async () => {
+    getAttachmentTextContentMock.mockResolvedValueOnce({
+      text: "<p>chart</p>",
+      originalContentType: "text/html",
+    });
+    const attachment = {
+      id: "att-1",
+      url: "/uploads/report.html",
+      filename: "report.html",
+      content_type: "text/html",
+      size_bytes: 0,
+    } as any;
+
+    renderWithQuery(<AttachmentList attachments={[attachment]} content="" />);
+
+    const frame = await waitFor(() => {
+      const f = document.querySelector("iframe") as HTMLIFrameElement | null;
+      expect(f).toBeTruthy();
+      return f!;
+    });
+    expect(frame.getAttribute("sandbox")).toBe("allow-scripts");
+    expect(frame.getAttribute("srcdoc")).toContain("<p>chart</p>");
+    // AttachmentCard chrome would render the filename as visible <p> text;
+    // HtmlAttachmentPreview replaces the row entirely.
+    expect(screen.queryByText("report.html")).toBeNull();
+  });
+});
diff --git a/packages/views/issues/components/comment-card.tsx b/packages/views/issues/components/comment-card.tsx
index 83fc557b3..47f2a6905 100644
--- a/packages/views/issues/components/comment-card.tsx
+++ b/packages/views/issues/components/comment-card.tsx
@@ -121,7 +121,7 @@ function DeleteCommentDialog({
 // Standalone attachment list — renders attachments not already in the markdown
 // ---------------------------------------------------------------------------
 
-function AttachmentList({ attachments, content, className }: { attachments?: Attachment[]; content?: string; className?: string }) {
+export function AttachmentList({ attachments, content, className }: { attachments?: Attachment[]; content?: string; className?: string }) {
   const download = useDownloadAttachment();
   const preview = useAttachmentPreview();
   if (!attachments?.length) return null;