My agent filled in every field on the form. It could not attach the three images.

I had an AI agent filling out a listing form on a web service. Every text field went in. It clicked Save Draft. All that was left was attaching three PNGs.

That part never worked.

I assumed that if it could fill the form, it could attach the files. Those turned out to be two different capabilities, gated in two different places, and the gate behaves differently depending on how you're running Claude Code. Same machine, same settings, same browser extension, different answer.

My setup: the Claude Code desktop app on Windows 11, the Claude in Chrome extension, and the computer-use desktop automation server.

The sanctioned route is closed first