[BUG] Remote-control sessions (browser/mobile) silently drop attachments — shown as sent, never reach the model

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Remote-control sessions (browser/mobile) silently drop attachments — shown as sent, never reach the model

Environment: Claude Code session hosted in VS Code; continued via Remote Control from a separate browser / mobile-app device. Windows host.

Repro:

1. Start a session on the host device (VS Code extension).
2. Continue/drive that session from a remote device (browser or mobile app) via remote control.
3. From the remote device, attach an image/file to a message and send.

Actual behavior:
the remote client shows the attachment as successfully attached/submitted, but the model receives the text with no attachment. Attachments sent from the original host device arrive normally.

Impact: Silent data loss — the user believes an image/file was shared; the model can't see it and responds as if nothing was attached. No error is surfaced on the remote client.

What Should Happen?

Expected:
An attachment sent from a remote-control client (browser/mobile) should reach the model in that same message, exactly as it does from the host device — full parity regardless of origin device. If it genuinely can't be delivered, the client should show an error at send time, not a successful "sent."

Error Messages/Logs

Steps to Reproduce

1. Start a session on the host device (VS Code extension).
2. Continue/drive that session from a remote device (browser or mobile app) via remote control.
3. From the remote device, attach an image/file to a message and send.

Claude Model

Not sure / Multiple models

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude Code 2.1.157 (Windows host, VS Code extension session; continued via remote-control browser/mobile client)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Claude Code 2.1.157 (Windows host, VS Code extension session; continued via remote-control browser/mobile client)