fix(agents): preserve prompt text during native image paste (#3250)

When the clipboard event carried no data (WebKitGTK pasting a screenshot), the composer started reading the image from the native clipboard but returned false, so CodeMirror still handled the paste and replaced the selected prompt text with an empty string. The handler now prevents the default paste and reports it as handled; the image is still attached when the native read returns one, and the prompt and selection stay as they were in every other outcome. The clipboard fixtures in the tests now implement getData so they go through CodeMirror's own paste path. This is the only native-clipboard paste fallback in the frontend.

Co-authored-by: LunarFeller <269972968+LunarFeller@users.noreply.github.com>

src/features/agents/Composer.tsx

@@ -742,6 +742,8 @@ export function Composer(props: ComposerProps) {
       return true;
     }
     if (isTauri() && !data.types.length) {
+      // CodeMirror would otherwise paste empty text over the selection.
+      e.preventDefault();
       pasteClipboardImage().catch((error: unknown) =>
         notifications().notify({
           level: "error",
@@ -749,7 +751,7 @@ export function Composer(props: ComposerProps) {
           body: String(error),
         }),
       );
-      return false;
+      return true;
     }
     const plain = data.getData("text/plain");
     if (plain && pasteCopied(plain, view)) {

src/features/agents/composerCommands.test.tsx

@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it, vi } from "vitest";
 import { sendKeyAction } from "./Composer";
 import { act, fireEvent, render, screen, waitFor, within } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
+import { EditorView } from "@codemirror/view";
 import type { AgentCommand, AgentProvider } from "@/bindings";
 
 const agentCommands = vi.fn();
@@ -53,7 +54,7 @@ import type { ProjectInfo } from "@/bindings";
 import { defaultTaskProject } from "./project";
 import { HomeEditor } from "./HomeEditor";
 import chipStyles from "./ReferenceChip.module.css";
-import { textOf, typeIn } from "./composerTesting";
+import { setCaret, textOf, typeIn } from "./composerTesting";
 import { composerDraft, HOME, updateComposer, useAgents } from "./store";
 import { emptyDraft } from "./composerModel";
 
@@ -280,19 +281,134 @@ describe("New Task composer paste", () => {
   it("attaches the clipboard's image when WebKitGTK pastes an empty clipboardData", async () => {
     render(<HomeEditor />);
     fireEvent.paste(screen.getByRole("textbox"), {
-      clipboardData: { types: [], files: [] },
+      clipboardData: { types: [], files: [], getData: () => "" },
     });
     await waitFor(() =>
       expect(composerDraft(HOME).images).toEqual([{ mimeType: "image/png", data: "iVBORw0KGgo=", name: "image" }]),
     );
+    expect(textOf(screen.getByRole("textbox"))).toBe("");
+  });
+
+  it.each([
+    { name: "part of the prompt selected", text: "keep prompt", anchor: 0, head: 4 },
+    { name: "the whole prompt selected", text: "keep prompt", anchor: 0, head: 11 },
+    { name: "a backwards selection", text: "keep prompt", anchor: 4, head: 0 },
+    { name: "a caret in the prompt", text: "keep prompt", anchor: 4, head: 4 },
+    { name: "a multiline Unicode selection", text: "保留🙂\nprompt", anchor: 0, head: 5 },
+  ])("keeps text and selection with $name when pasting a native image", async ({ text, anchor, head }) => {
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, text);
+    setCaret(box, anchor, head);
+    const allowed = fireEvent.paste(box, {
+      clipboardData: { types: [], files: [], getData: () => "" },
+    });
+    expect(textOf(box)).toBe(text);
+    expect(allowed).toBe(false);
+    await waitFor(() => expect(composerDraft(HOME).images).toHaveLength(1));
+    expect(clipboardImage).toHaveBeenCalledTimes(1);
+    expect(composerDraft(HOME).text).toBe(text);
+    expect(EditorView.findFromDOM(box)!.state.selection.main).toMatchObject({ anchor, head });
+  });
+
+  it.each([
+    { name: "no image", result: { status: "ok", data: null } },
+    { name: "an invalid image", result: { status: "ok", data: "not an image" } },
+    { name: "an error", result: { status: "error", error: { kind: "internal", message: "clipboard busy" } } },
+  ])("keeps selected text when the native clipboard returns $name", async ({ result }) => {
+    clipboardImage.mockResolvedValueOnce(result);
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, "keep prompt");
+    setCaret(box, 0, 4);
+    await act(async () => {
+      fireEvent.paste(box, { clipboardData: { types: [], files: [], getData: () => "" } });
+    });
+    expect(clipboardImage).toHaveBeenCalledTimes(1);
+    expect(textOf(box)).toBe("keep prompt");
+    expect(composerDraft(HOME)).toMatchObject({ text: "keep prompt", images: [] });
+    expect(EditorView.findFromDOM(box)!.state.selection.main).toMatchObject({ anchor: 0, head: 4 });
+  });
+
+  it("keeps selected text when the native clipboard request rejects", async () => {
+    clipboardImage.mockRejectedValueOnce(new Error("clipboard unavailable"));
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, "keep prompt");
+    setCaret(box, 0, 4);
+    await act(async () => {
+      fireEvent.paste(box, { clipboardData: { types: [], files: [], getData: () => "" } });
+    });
+    expect(textOf(box)).toBe("keep prompt");
+    expect(composerDraft(HOME)).toMatchObject({ text: "keep prompt", images: [] });
+  });
+
+  it("keeps edits made while the native image is being read", async () => {
+    let finish!: (result: { status: "ok"; data: string }) => void;
+    clipboardImage.mockReturnValueOnce(new Promise((resolve) => (finish = resolve)));
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, "keep prompt");
+    setCaret(box, 0, 4);
+    fireEvent.paste(box, { clipboardData: { types: [], files: [], getData: () => "" } });
+    expect(textOf(box)).toBe("keep prompt");
+    typeIn(box, "edited while reading");
+    await act(async () => finish({ status: "ok", data: "data:image/png;base64,iVBORw0KGgo=" }));
+    expect(textOf(box)).toBe("edited while reading");
+    expect(composerDraft(HOME)).toMatchObject({ text: "edited while reading", images: [expect.anything()] });
+  });
+
+  it("attaches an image file without replacing selected text or reading the native clipboard", async () => {
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, "keep prompt");
+    setCaret(box, 0, 4);
+    fireEvent.paste(box, {
+      clipboardData: {
+        types: ["Files", "text/plain"],
+        files: [new File(["image"], "shot.png", { type: "image/png" })],
+        getData: () => "image caption",
+      },
+    });
+    await waitFor(() => expect(composerDraft(HOME).images).toHaveLength(1));
+    expect(composerDraft(HOME).images[0]).toMatchObject({ name: "shot.png", mimeType: "image/png" });
+    expect(textOf(box)).toBe("keep prompt");
+    expect(clipboardImage).not.toHaveBeenCalled();
   });
 
   it("leaves a text paste to the text box", () => {
     render(<HomeEditor />);
-    fireEvent.paste(screen.getByRole("textbox"), {
-      clipboardData: { types: ["text/plain"], files: [] },
+    const box = screen.getByRole("textbox");
+    const text = "pasted text";
+    fireEvent.paste(box, {
+      clipboardData: {
+        types: ["text/plain"],
+        files: [],
+        getData: (type: string) => (type === "text/plain" ? text : ""),
+      },
     });
     expect(clipboardImage).not.toHaveBeenCalled();
+    expect(textOf(box)).toBe(text);
+    expect(composerDraft(HOME).text).toBe(text);
+  });
+
+  it.each([
+    { name: "plain text", types: ["text/plain"], format: "text/plain", text: "new", native: true },
+    { name: "rich text", types: ["text/html", "text/plain"], format: "text/plain", text: "新的🙂", native: true },
+    { name: "a URI", types: ["text/uri-list"], format: "text/uri-list", text: "https://example.com", native: true },
+    { name: "browser text", types: ["text/plain"], format: "text/plain", text: "new", native: false },
+  ])("still replaces selected text when pasting $name", ({ types, format, text, native }) => {
+    vi.mocked(isTauri).mockReturnValue(native);
+    render(<HomeEditor />);
+    const box = screen.getByRole("textbox");
+    typeIn(box, "keep old prompt");
+    setCaret(box, 5, 8);
+    fireEvent.paste(box, {
+      clipboardData: { types, files: [], getData: (type: string) => (type === format ? text : "") },
+    });
+    expect(textOf(box)).toBe(`keep ${text} prompt`);
+    expect(composerDraft(HOME)).toMatchObject({ text: `keep ${text} prompt`, images: [] });
+    expect(clipboardImage).not.toHaveBeenCalled();
   });
 });