feat(browser): add paste-files command for clipboard-paste file uploads

Wires a new IPage.pasteFiles primitive plus a browser paste-files CLI verb so adapters can attach local files into chat composers and rich editors whose upload flow only listens to clipboard paste events.

Closes #1843

Author: Benjamin-eecs

extension/dist/background.js

@@ -345,6 +345,46 @@ async function insertText(tabId, text) {
   await ensureAttached(tabId);
   await chrome.debugger.sendCommand({ tabId }, "Input.insertText", { text });
 }
+async function pasteClipboardFiles(tabId, files, selector) {
+  await ensureAttached(tabId);
+  const targetExpr = selector ? `document.querySelector(${JSON.stringify(selector)})` : "document.activeElement && document.activeElement !== document.body ? document.activeElement : document.body";
+  const expression = `
+    (() => {
+      const target = ${targetExpr};
+      if (!target) return { ok: false, reason: 'no_target' };
+      const files = ${JSON.stringify(files)};
+      const dt = new DataTransfer();
+      for (const f of files) {
+        const binary = atob(f.base64);
+        const bytes = new Uint8Array(binary.length);
+        for (let i = 0; i < binary.length; i++) bytes[i] = binary.charCodeAt(i);
+        const blob = new Blob([bytes], { type: f.mimeType });
+        dt.items.add(new File([blob], f.name, { type: f.mimeType }));
+      }
+      const event = new ClipboardEvent('paste', {
+        clipboardData: dt,
+        bubbles: true,
+        cancelable: true,
+      });
+      const delivered = target.dispatchEvent(event);
+      return { ok: true, count: files.length, delivered };
+    })()
+  `;
+  const result = await chrome.debugger.sendCommand({ tabId }, "Runtime.evaluate", {
+    expression,
+    returnByValue: true
+  });
+  if (result.exceptionDetails) {
+    const description = result.exceptionDetails.exception?.description ?? result.exceptionDetails.text ?? "Unknown error";
+    throw new Error(`paste-files evaluate failed: ${description}`);
+  }
+  const value = result.result?.value;
+  if (!value?.ok) {
+    const reason = value?.reason === "no_target" ? "paste-files target not found (no focused element and no --target selector match)" : "paste-files dispatch returned no acknowledgement";
+    throw new Error(reason);
+  }
+  return value.count ?? files.length;
+}
 function registerFrameTracking() {
   registerFrameTargetCleanup();
   chrome.debugger.onEvent.addListener((source, method, params) => {
@@ -1475,6 +1515,8 @@ async function handleCommand(cmd) {
         return await handleSetFileInput(cmd, leaseKey);
       case "insert-text":
         return await handleInsertText(cmd, leaseKey);
+      case "paste-files":
+        return await handlePasteFiles(cmd, leaseKey);
       case "bind":
         return await handleBind(cmd, leaseKey);
       case "network-capture-start":
@@ -2020,6 +2062,20 @@ async function handleInsertText(cmd, leaseKey) {
     return { id: cmd.id, ok: false, error: err instanceof Error ? err.message : String(err) };
   }
 }
+async function handlePasteFiles(cmd, leaseKey) {
+  const files = cmd.clipboardFiles;
+  if (!Array.isArray(files) || files.length === 0) {
+    return { id: cmd.id, ok: false, error: "Missing or empty clipboardFiles array" };
+  }
+  const cmdTabId = await resolveCommandTabId(cmd);
+  const tabId = await resolveTabId(cmdTabId, leaseKey);
+  try {
+    const count = await pasteClipboardFiles(tabId, files, cmd.selector);
+    return pageScopedResult(cmd.id, tabId, { count });
+  } catch (err) {
+    return { id: cmd.id, ok: false, error: err instanceof Error ? err.message : String(err) };
+  }
+}
 async function handleNetworkCaptureStart(cmd, leaseKey) {
   const cmdTabId = await resolveCommandTabId(cmd);
   const tabId = await resolveTabId(cmdTabId, leaseKey);

extension/src/background.ts

@@ -1117,6 +1117,8 @@ async function handleCommand(cmd: Command): Promise<Result> {
         return await handleSetFileInput(cmd, leaseKey);
       case 'insert-text':
         return await handleInsertText(cmd, leaseKey);
+      case 'paste-files':
+        return await handlePasteFiles(cmd, leaseKey);
       case 'bind':
         return await handleBind(cmd, leaseKey);
       case 'network-capture-start':
@@ -1769,6 +1771,21 @@ async function handleInsertText(cmd: Command, leaseKey: string): Promise<Result>
   }
 }
 
+async function handlePasteFiles(cmd: Command, leaseKey: string): Promise<Result> {
+  const files = cmd.clipboardFiles;
+  if (!Array.isArray(files) || files.length === 0) {
+    return { id: cmd.id, ok: false, error: 'Missing or empty clipboardFiles array' };
+  }
+  const cmdTabId = await resolveCommandTabId(cmd);
+  const tabId = await resolveTabId(cmdTabId, leaseKey);
+  try {
+    const count = await executor.pasteClipboardFiles(tabId, files, cmd.selector);
+    return pageScopedResult(cmd.id, tabId, { count });
+  } catch (err) {
+    return { id: cmd.id, ok: false, error: err instanceof Error ? err.message : String(err) };
+  }
+}
+
 async function handleNetworkCaptureStart(cmd: Command, leaseKey: string): Promise<Result> {
   const cmdTabId = await resolveCommandTabId(cmd);
   const tabId = await resolveTabId(cmdTabId, leaseKey);

extension/src/cdp.ts

@@ -510,6 +510,65 @@ export async function insertText(
   await chrome.debugger.sendCommand({ tabId }, 'Input.insertText', { text });
 }
 
+/**
+ * Dispatch a synthesized ClipboardEvent('paste') with a DataTransfer payload
+ * built from the supplied files on the focused element, or on the element
+ * matched by `selector` when provided. Mirrors the inline DataTransfer +
+ * dispatch flow that adapters such as instagram/post, twitter/post,
+ * chatgpt/utils and xiaohongshu/publish currently reinvent.
+ */
+export async function pasteClipboardFiles(
+  tabId: number,
+  files: Array<{ name: string; mimeType: string; base64: string }>,
+  selector?: string,
+): Promise<number> {
+  await ensureAttached(tabId);
+  const targetExpr = selector
+    ? `document.querySelector(${JSON.stringify(selector)})`
+    : 'document.activeElement && document.activeElement !== document.body ? document.activeElement : document.body';
+  const expression = `
+    (() => {
+      const target = ${targetExpr};
+      if (!target) return { ok: false, reason: 'no_target' };
+      const files = ${JSON.stringify(files)};
+      const dt = new DataTransfer();
+      for (const f of files) {
+        const binary = atob(f.base64);
+        const bytes = new Uint8Array(binary.length);
+        for (let i = 0; i < binary.length; i++) bytes[i] = binary.charCodeAt(i);
+        const blob = new Blob([bytes], { type: f.mimeType });
+        dt.items.add(new File([blob], f.name, { type: f.mimeType }));
+      }
+      const event = new ClipboardEvent('paste', {
+        clipboardData: dt,
+        bubbles: true,
+        cancelable: true,
+      });
+      const delivered = target.dispatchEvent(event);
+      return { ok: true, count: files.length, delivered };
+    })()
+  `;
+  const result = await chrome.debugger.sendCommand({ tabId }, 'Runtime.evaluate', {
+    expression,
+    returnByValue: true,
+  }) as {
+    result?: { value?: { ok?: boolean; reason?: string; count?: number; delivered?: boolean } };
+    exceptionDetails?: { exception?: { description?: string }; text?: string };
+  };
+  if (result.exceptionDetails) {
+    const description = result.exceptionDetails.exception?.description ?? result.exceptionDetails.text ?? 'Unknown error';
+    throw new Error(`paste-files evaluate failed: ${description}`);
+  }
+  const value = result.result?.value;
+  if (!value?.ok) {
+    const reason = value?.reason === 'no_target'
+      ? 'paste-files target not found (no focused element and no --target selector match)'
+      : 'paste-files dispatch returned no acknowledgement';
+    throw new Error(reason);
+  }
+  return value.count ?? files.length;
+}
+
 export function registerFrameTracking(): void {
   registerFrameTargetCleanup();
   chrome.debugger.onEvent.addListener((source, method, params: any) => {

extension/src/protocol.ts

@@ -15,6 +15,7 @@ export type Action =
   | 'sessions'
   | 'set-file-input'
   | 'insert-text'
+  | 'paste-files'
   | 'bind'
   | 'network-capture-start'
   | 'network-capture-read'
@@ -61,6 +62,8 @@ export interface Command {
   selector?: string;
   /** Raw text payload for insert-text action */
   text?: string;
+  /** Base64-encoded files for paste-files action (name, mimeType, base64 content per entry) */
+  clipboardFiles?: Array<{ name: string; mimeType: string; base64: string }>;
   /** URL substring filter pattern for network capture actions */
   pattern?: string;
   /** Download wait timeout in milliseconds */

src/browser/daemon-client.ts

@@ -21,7 +21,7 @@ function generateId(): string {
 
 export interface DaemonCommand {
   id: string;
-  action: 'exec' | 'navigate' | 'tabs' | 'cookies' | 'screenshot' | 'close-window' | 'set-file-input' | 'insert-text' | 'bind' | 'network-capture-start' | 'network-capture-read' | 'wait-download' | 'cdp' | 'frames';
+  action: 'exec' | 'navigate' | 'tabs' | 'cookies' | 'screenshot' | 'close-window' | 'set-file-input' | 'insert-text' | 'paste-files' | 'bind' | 'network-capture-start' | 'network-capture-read' | 'wait-download' | 'cdp' | 'frames';
   /** Target page identity (targetId). Cross-layer contract with the extension. */
   page?: string;
   code?: string;
@@ -47,6 +47,8 @@ export interface DaemonCommand {
   selector?: string;
   /** Raw text payload for insert-text action */
   text?: string;
+  /** Base64-encoded files for paste-files action (name, mimeType, base64 content per entry) */
+  clipboardFiles?: Array<{ name: string; mimeType: string; base64: string }>;
   /** URL substring filter pattern for network capture */
   pattern?: string;
   /** Download wait timeout in milliseconds */

src/browser/page.test.ts

@@ -1,3 +1,6 @@
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
 import { beforeEach, describe, expect, it, vi } from 'vitest';
 
 const { sendCommandMock, sendCommandFullMock } = vi.hoisted(() => ({
@@ -472,3 +475,54 @@ describe('Page.screenshot', () => {
     expect(args.fullPage).toBeUndefined();
   });
 });
+
+describe('Page.pasteFiles', () => {
+  beforeEach(() => {
+    sendCommandMock.mockReset();
+    sendCommandFullMock.mockReset();
+    warnMock.mockReset();
+  });
+
+  it('base64-encodes provided files and forwards them as clipboardFiles', async () => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'opencli-paste-'));
+    const filePath = path.join(dir, 'note.png');
+    fs.writeFileSync(filePath, Buffer.from([0x89, 0x50, 0x4e, 0x47]));
+
+    try {
+      sendCommandMock.mockResolvedValueOnce({ count: 1 });
+
+      const page = new Page('default');
+      await expect(page.pasteFiles([filePath], '#composer')).resolves.toBeUndefined();
+
+      const call = sendCommandMock.mock.calls.at(-1);
+      expect(call?.[0]).toBe('paste-files');
+      const args = call?.[1] as Record<string, unknown>;
+      expect(args.selector).toBe('#composer');
+      expect(args.clipboardFiles).toEqual([
+        { name: 'note.png', mimeType: 'image/png', base64: 'iVBORw==' },
+      ]);
+    } finally {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  });
+
+  it('rejects an empty files list before reaching the daemon', async () => {
+    const page = new Page('default');
+    await expect(page.pasteFiles([])).rejects.toThrow('pasteFiles requires at least one file path');
+    expect(sendCommandMock).not.toHaveBeenCalled();
+  });
+
+  it('throws when the extension returns no count (unsupported action)', async () => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'opencli-paste-'));
+    const filePath = path.join(dir, 'note.txt');
+    fs.writeFileSync(filePath, 'hi');
+
+    try {
+      sendCommandMock.mockResolvedValueOnce({});
+      const page = new Page('default');
+      await expect(page.pasteFiles([filePath])).rejects.toThrow(/no count/);
+    } finally {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  });
+});

src/browser/page.ts

@@ -9,6 +9,8 @@
  * page-scoped operations target the correct page without guessing.
  */
 
+import * as fs from 'node:fs';
+import * as path from 'node:path';
 import type { BrowserCookie, BrowserDownloadWaitResult, BrowserEvaluateFunction, ScreenshotOptions } from '../types.js';
 import { sendCommand, sendCommandFull } from './daemon-client.js';
 import { buildEvaluateExpression } from './utils.js';
@@ -19,6 +21,33 @@ import { BasePage } from './base-page.js';
 import { classifyBrowserError } from './errors.js';
 import { log } from '../logger.js';
 
+/**
+ * Extension-to-MIME map for `pasteFiles`. Covers the file types adapters in
+ * this repo currently DataTransfer into chat composers and rich editors;
+ * unknown extensions fall back to `application/octet-stream`, which browser
+ * paste handlers usually still accept because they sniff content themselves.
+ */
+const CLIPBOARD_MIME_BY_EXT: Record<string, string> = {
+  '.jpg': 'image/jpeg',
+  '.jpeg': 'image/jpeg',
+  '.png': 'image/png',
+  '.gif': 'image/gif',
+  '.webp': 'image/webp',
+  '.bmp': 'image/bmp',
+  '.svg': 'image/svg+xml',
+  '.pdf': 'application/pdf',
+  '.txt': 'text/plain',
+  '.md': 'text/markdown',
+  '.json': 'application/json',
+  '.csv': 'text/csv',
+  '.html': 'text/html',
+  '.htm': 'text/html',
+  '.mp4': 'video/mp4',
+  '.webm': 'video/webm',
+  '.mp3': 'audio/mpeg',
+  '.wav': 'audio/wav',
+};
+
 function isUnsupportedNetworkCaptureError(err: unknown): boolean {
   const message = err instanceof Error ? err.message : String(err);
   const normalized = message.toLowerCase();
@@ -323,6 +352,30 @@ export class Page extends BasePage {
     }
   }
 
+  async pasteFiles(files: string[], selector?: string): Promise<void> {
+    if (!Array.isArray(files) || files.length === 0) {
+      throw new Error('pasteFiles requires at least one file path');
+    }
+    const clipboardFiles = files.map((filePath) => {
+      const absPath = path.resolve(filePath);
+      const buffer = fs.readFileSync(absPath);
+      const ext = path.extname(absPath).toLowerCase();
+      return {
+        name: path.basename(absPath),
+        mimeType: CLIPBOARD_MIME_BY_EXT[ext] ?? 'application/octet-stream',
+        base64: buffer.toString('base64'),
+      };
+    });
+    const result = await sendCommand('paste-files', {
+      clipboardFiles,
+      selector,
+      ...this._cmdOpts(),
+    }) as { count?: number };
+    if (!result?.count) {
+      throw new Error('pasteFiles returned no count; command may not be supported by the extension');
+    }
+  }
+
   async frames(): Promise<Array<{ index: number; frameId: string; url: string; name: string }>> {
     const result = await sendCommand('frames', { ...this._cmdOpts() });
     return Array.isArray(result) ? result : [];