Your image link
quietly doesn't load.

The problem

You want a screenshot at the top of a PR. Every path that looks like it should work fails — and most of them fail silently, so you only find out when a reviewer sees a broken image icon.

Why the obvious paths fail

• There is no attachment API. GitHub's only uploader is a browser drag-drop onto a classic Markdown editor. gh can't do it.
• raw.githubusercontent.com from a private repo → does not render. GitHub proxies images through camo, and camo can't authenticate. Dead end.
• The file_upload MCP tool → currently rejects host paths (regressed). Don't rely on it.
• Synthetic cmd+v paste → unreliable; the key event never delivers image bytes to GitHub's paste handler.

The turn

Stop trying to host the image. Make GitHub's real uploader run. Put the image on the clipboard as base64 text, then dispatch a genuine drop event carrying a reconstructed File onto a classic editor's <file-attachment> element. GitHub uploads it for real and inserts the markup — which we harvest. The bytes ride the OS clipboard; they never pass through the agent's context.

The classic editor only exists in a few places — not the React /issues/new page. The reliable one is any repo's wiki new-page, used purely as an uploader and never saved. The asset persists on its own.

The receipt

Clipboard → drop → URL → body. Four moves:

# 1. image onto the clipboard as base64 text (macOS; note the -i)
base64 -i /path/to/image.png | tr -d '\n' | pbcopy

# 2. open a CLASSIC editor and prove it is one — both must be true
#    https://github.com/<owner>/<repo>/wiki/_new
({ hasFileAttachment: !!document.querySelector('file-attachment'),
   hasBody: !!document.querySelector('#gollum-editor-body') })

# 3. click the body for OS focus, then run scripts/drop-and-harvest.js
#    → { url, imgTag }

# 4. spend the URL
gh pr edit <N> --body-file body.md   # <img width="1200" src="$URL" />

When not to

• The image already has a public, renderable URL — just paste it.
• The repo is public and the file is committed — raw.githubusercontent.com is fine there.
• Chrome MCP isn't available. The whole mechanism is a real browser driving a real uploader.