diff --git a/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.spec.tsx b/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.spec.tsx
new file mode 100644
--- /dev/null
+++ b/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.spec.tsx
@@ -0,0 +1,105 @@
+import { act } from "react";
+import { createRoot, Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { usePromptBoxDrop, UsePromptBoxDropOptions } from "./usePromptBoxDrop";
+
+const { error } = vi.hoisted(() => ({ error: vi.fn() }));
+vi.mock("@storyteller/ui-toaster", () => ({ toast: { error } }));
+vi.mock("@storyteller/tauri-utils", () => ({ IsDesktopApp: () => false }));
+vi.mock("@storyteller/icons", () => ({ DynamicIcon: () => null }));
+vi.mock("lucide-react", () => ({ ImagesIcon: () => null, MusicIcon: () => null, VideoIcon: () => null }));
+vi.mock("tailwind-merge", () => ({ twMerge: (...values: string[]) => values.join(" ") }));
+
+let root: Root;
+let container: HTMLDivElement;
+
+beforeEach(() => {
+  globalThis.IS_REACT_ACT_ENVIRONMENT = true;
+  error.mockReset();
+  container = document.createElement("div");
+  document.body.appendChild(container);
+  root = createRoot(container);
+});
+
+afterEach(() => {
+  act(() => root.unmount());
+  container.remove();
+});
+
+describe("prompt reference file routing", () => {
+  it.each(["drop", "paste"] as const)("accepts M4A reported as video/mp4 through %s", (transport) => {
+    const receive = mount({ acceptsAudio: true });
+    const file = new File(["audio"], "voice.m4a", { type: "video/mp4" });
+    deliver(transport, [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [], videos: [], audios: [file] });
+    expect(error).not.toHaveBeenCalled();
+  });
+
+  it("routes M4A into audio when both video and audio are supported", () => {
+    const receive = mount({ acceptsAudio: true, acceptsVideos: true });
+    const file = new File(["audio"], "VOICE.M4A", { type: "video/mp4" });
+    deliver("drop", [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [], videos: [], audios: [file] });
+  });
+
+  it("does not send M4A to a video-only model", () => {
+    const receive = mount({ acceptsVideos: true });
+    deliver("drop", [new File(["audio"], "voice.m4a", { type: "video/mp4" })]);
+    expect(receive).not.toHaveBeenCalled();
+    expect(error).toHaveBeenCalledWith("Audio references aren't available here");
+  });
+
+  it("preserves genuine MP4 video references", () => {
+    const receive = mount({ acceptsVideos: true });
+    const file = new File(["video"], "clip.mp4", { type: "video/mp4" });
+    deliver("drop", [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [], videos: [file], audios: [] });
+  });
+
+  it("preserves audio MIME routing without a recognized extension", () => {
+    const receive = mount({ acceptsAudio: true });
+    const file = new File(["audio"], "recording", { type: "audio/mpeg" });
+    deliver("paste", [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [], videos: [], audios: [file] });
+  });
+
+  it("preserves extension fallback for empty MIME", () => {
+    const receive = mount({ acceptsAudio: true });
+    const file = new File(["audio"], "voice.m4a");
+    deliver("drop", [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [], videos: [], audios: [file] });
+  });
+
+  it("preserves image routing", () => {
+    const receive = mount({ acceptsImages: true });
+    const file = new File(["image"], "photo.png", { type: "image/png" });
+    deliver("drop", [file]);
+    expect(receive).toHaveBeenCalledWith({ images: [file], videos: [], audios: [] });
+  });
+
+  it("still rejects audio when the model only accepts images", () => {
+    const receive = mount({ acceptsImages: true });
+    deliver("paste", [new File(["audio"], "voice.mp3", { type: "audio/mpeg" })]);
+    expect(receive).not.toHaveBeenCalled();
+    expect(error).toHaveBeenCalledWith("Audio references aren't available here");
+  });
+});
+
+function mount(capabilities: Partial<UsePromptBoxDropOptions>) {
+  const receive = vi.fn();
+  function Zone() {
+    const drop = usePromptBoxDrop({ acceptsAudio: false, acceptsVideos: false, acceptsImages: false, ...capabilities, onDropFiles: receive });
+    return <div {...drop.dropZoneProps} data-testid="zone" />;
+  }
+  act(() => root.render(<Zone />));
+  return receive;
+}
+
+function deliver(transport: "drop" | "paste", files: File[]) {
+  const event = new Event(transport, { bubbles: true, cancelable: true });
+  Object.defineProperty(event, transport === "drop" ? "dataTransfer" : "clipboardData", { value: { files, types: ["Files"] } });
+  act(() => {
+    const target = transport === "drop" ? container.querySelector('[data-testid="zone"]')! : window;
+    target.dispatchEvent(event);
+  });
+}
diff --git a/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.tsx b/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.tsx
--- a/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.tsx
+++ b/frontend/libs/components/promptbox/src/lib/deck/usePromptBoxDrop.tsx
@@ -4,6 +4,7 @@ import { ImagesIcon, MusicIcon, VideoIcon } from "lucide-react";
 import { DynamicIcon } from "@storyteller/icons";
 import { toast } from "@storyteller/ui-toaster";
 import { IsDesktopApp } from "@storyteller/tauri-utils";
+import { isAudioFile } from "../common/audioFiles";
 
 // ── Types ───────────────────────────────────────────────────────────────
 
@@ -175,7 +176,11 @@ export function usePromptBoxDrop({
     const rejectedKinds = new Set<DropKind>();
     let unknownCount = 0;
     for (const file of files) {
-      const kind = kindOfMime(file.type) ?? kindOfPath(file.name);
+      // Some platforms report M4A as video/mp4; use the same audio guard
+      // as the reference picker before trusting that container MIME type.
+      const kind = isAudioFile(file)
+        ? "audio"
+        : (kindOfMime(file.type) ?? kindOfPath(file.name));
       if (kind === null) {
         unknownCount++;
       } else if (!acceptsKind(kind)) {