diff --git a/canvas/src/components/tabs/chat/__tests__/AttachmentAudio.test.tsx b/canvas/src/components/tabs/chat/__tests__/AttachmentAudio.test.tsx
new file mode 100644
index 00000000..bd8c946e
--- /dev/null
+++ b/canvas/src/components/tabs/chat/__tests__/AttachmentAudio.test.tsx
@@ -0,0 +1,275 @@
+// @vitest-environment jsdom
+/**
+ * AttachmentAudio — inline native HTML5 <audio> player for chat attachments.
+ *
+ * Per RFC #2991 PR-2: platform-auth URIs fetch bytes → Blob → ObjectURL;
+ * external URIs use the raw URL directly. State machine: idle → loading →
+ * ready/error. Loading skeleton shown while fetching. Error falls back to
+ * AttachmentChip. Blob URL cleaned up on unmount / re-run.
+ *
+ * NOTE: No @testing-library/jest-dom import — use DOM APIs for assertions.
+ *
+ * Covers:
+ *   - Renders loading skeleton with aria-label while fetching
+ *   - Renders <audio> element with correct src when ready
+ *   - Error state renders AttachmentChip fallback
+ *   - tone=user applies blue border class
+ *   - tone=agent applies neutral border class
+ *   - Filename label shown before audio controls
+ *   - onDownload called when error chip is clicked
+ *   - Cleans up blob URL on unmount
+ *   - External URI uses direct href without fetch
+ */
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { cleanup, fireEvent, render } from "@testing-library/react";
+import React from "react";
+
+import { AttachmentAudio } from "../AttachmentAudio";
+import type { ChatAttachment } from "../types";
+
+// ─── Mocks ───────────────────────────────────────────────────────────────────
+
+const mockResolveAttachmentHref = vi.fn<(id: string, uri: string) => string>(
+  (id, uri) => `https://api.moleculesai.app/attachments/${uri}`,
+);
+const mockIsPlatformAttachment = vi.fn<(uri: string) => boolean>(() => true);
+
+vi.mock("../uploads", () => ({
+  isPlatformAttachment: (uri: string) => mockIsPlatformAttachment(uri),
+  resolveAttachmentHref: (id: string, uri: string) =>
+    mockResolveAttachmentHref(id, uri),
+}));
+
+vi.mock("@/lib/api", () => ({
+  platformAuthHeaders: () => ({ Authorization: "Bearer test-token" }),
+}));
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+function makeAttachment(name: string, size?: number): ChatAttachment {
+  return { name, uri: `workspace:/tmp/${name}`, size };
+}
+
+afterEach(() => {
+  cleanup();
+  vi.restoreAllMocks();
+  vi.resetModules();
+});
+
+// ─── Fetch mock helpers ──────────────────────────────────────────────────────
+
+function mockFetchOk(body: string, contentType = "audio/mpeg") {
+  const blob = new Blob([body], { type: contentType });
+  global.fetch = vi.fn((href: string, opts?: RequestInit) => {
+    void href;
+    void opts;
+    return Promise.resolve({
+      ok: true,
+      status: 200,
+      blob: () => Promise.resolve(blob),
+      headers: new Map([["content-type", contentType]]),
+    }) as unknown as Response;
+  });
+}
+
+function mockFetchError() {
+  global.fetch = vi.fn(() =>
+    Promise.resolve({ ok: false, status: 500 }) as unknown as Response,
+  );
+}
+
+// ─── Idle/Loading state ─────────────────────────────────────────────────────
+
+describe("AttachmentAudio — idle/loading", () => {
+  beforeEach(() => {
+    mockFetchOk("audiodata");
+  });
+
+  it("renders loading skeleton with aria-label", () => {
+    const att = makeAttachment("podcast.mp3", 1024 * 512);
+    const { container } = render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="user"
+      />,
+    );
+    const skeleton = container.querySelector('[aria-label]') as HTMLElement;
+    expect(skeleton?.getAttribute("aria-label")).toContain("podcast.mp3");
+    expect(skeleton?.getAttribute("aria-label")).toContain("Loading");
+  });
+
+  it("loading skeleton has correct dimensions", () => {
+    const att = makeAttachment("track.mp3");
+    const { container } = render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="agent"
+      />,
+    );
+    const skeleton = container.querySelector('[aria-label]') as HTMLElement;
+    expect(skeleton?.style.width).toBe("280px");
+    expect(skeleton?.style.height).toBe("40px");
+  });
+});
+
+// ─── Ready state ─────────────────────────────────────────────────────────────
+
+describe("AttachmentAudio — ready", () => {
+  beforeEach(() => {
+    mockFetchOk("audiodata");
+  });
+
+  it("renders <audio> element with correct src when ready", async () => {
+    const att = makeAttachment("clip.mp3", 1024 * 512);
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="user"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const audio = document.querySelector("audio") as HTMLAudioElement;
+    expect(audio.src).toMatch(/^blob:/);
+    expect(audio.hasAttribute("controls")).toBe(true);
+    expect(audio.getAttribute("preload")).toBe("metadata");
+  });
+
+  it("tone=user applies blue border class", async () => {
+    mockFetchOk("data");
+    const att = makeAttachment("clip.mp3");
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="user"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const audio = document.querySelector("audio");
+    const container = audio?.closest("div");
+    expect(container?.className).toContain("blue-400");
+  });
+
+  it("tone=agent applies neutral border class (no blue)", async () => {
+    mockFetchOk("data");
+    const att = makeAttachment("clip.mp3");
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="agent"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const audio = document.querySelector("audio");
+    const container = audio?.closest("div");
+    expect(container?.className).not.toContain("blue-400");
+  });
+
+  it("filename label shown before audio controls", async () => {
+    mockFetchOk("data");
+    const att = makeAttachment("my-podcast-episode.mp3");
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="agent"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const container = document.querySelector("audio")?.closest("div");
+    expect(container?.textContent ?? "").toContain("my-podcast-episode.mp3");
+  });
+});
+
+// ─── Error state ─────────────────────────────────────────────────────────────
+
+describe("AttachmentAudio — error", () => {
+  it("renders AttachmentChip fallback when fetch fails", async () => {
+    mockFetchError();
+    const onDownload = vi.fn();
+    const att = makeAttachment("broken.mp3", 256);
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={onDownload}
+        tone="agent"
+      />,
+    );
+    await vi.waitFor(() => {
+      const chip = document.querySelector("button");
+      expect(chip).toBeTruthy();
+      expect(chip?.textContent).toContain("broken.mp3");
+    });
+    const chip = document.querySelector("button") as HTMLButtonElement;
+    chip.click();
+    expect(onDownload).toHaveBeenCalledWith(att);
+  });
+});
+
+// ─── Cleanup ─────────────────────────────────────────────────────────────────
+
+describe("AttachmentAudio — blob URL cleanup", () => {
+  it("creates blob URL on mount and cleans up on unmount", async () => {
+    mockFetchOk("audiodata");
+    const att = makeAttachment("clip.mp3");
+    const { unmount } = render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="user"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const audio = document.querySelector("audio") as HTMLAudioElement;
+    const blobUrl = audio.src;
+    expect(blobUrl).toMatch(/^blob:/);
+    unmount();
+    expect(document.querySelector("audio")).toBeNull();
+  });
+});
+
+// ─── External URI ───────────────────────────────────────────────────────────
+
+describe("AttachmentAudio — external URI", () => {
+  it("uses direct href for external URIs without fetch", async () => {
+    mockIsPlatformAttachment.mockReturnValue(false);
+    const externalUri = "https://example.com/audio.mp3";
+    const att = makeAttachment("audio.mp3");
+    att.uri = externalUri;
+    render(
+      <AttachmentAudio
+        workspaceId="ws1"
+        attachment={att}
+        onDownload={vi.fn()}
+        tone="user"
+      />,
+    );
+    await vi.waitFor(() => {
+      expect(document.querySelector("audio")).toBeTruthy();
+    });
+    const audio = document.querySelector("audio") as HTMLAudioElement;
+    expect(audio.src).toContain("example.com/audio.mp3");
+  });
+});