GitHub plugin: screenshots in PR descriptions/comments don't load in the PR view

[Andrew-Brevard]

Summary

Screenshots in a pull request's description and comments don't load in the GitHub plugin's PR view. The image area stays empty or broken, while the same PR shows the images fine on github.com.

Steps to reproduce

1. Open a PR whose body has a screenshot pasted into GitHub (e.g. ![image](https://github.com/user-attachments/assets/<id>) or <img src="https://github.com/user-attachments/assets/<id>">).
2. Open that PR in bb's GitHub plugin (full page or the thread's right sidebar).
3. The screenshot doesn't render.

Likely cause (github plugin 0.2.1)

The PR body renderer matches ![..](..) / <img> and outputs a plain <img src={rawUrl} loading="lazy"> for any http(s) URL. For private repos, github.com/user-attachments/assets/... (and older private-user-images links) require an authenticated GitHub session. GitHub's own rendered HTML swaps them for short-lived signed private-user-images.githubusercontent.com/...?jwt=... URLs. The raw URL, requested from bb's origin without GitHub cookies, gets redirected to a login page or 404, so the image fails.

Suggested fix

• Fetch the rendered body (gh api with Accept: application/vnd.github.html+json, or GraphQL bodyHTML) to get signed image URLs, or
• Proxy image requests through the plugin server using the user's gh token.
• At minimum, fall back to a link to the image (or alt text) when it fails to load, so it isn't just blank.

[bb-slop-cop]

🚨 SLOP COP 🚨 · new-issue-autopilot

• Classification: Bug · Priority Medium · Effort Medium · labels ui, github, partial-repro.
• Reproduction report: PARTIALLY REPRODUCED, root-cause confidence medium.
• Root cause: PR Markdown renders raw image URLs without a failed-load fallback. The proposed private-attachment authentication mechanism remains unverified.
• Reproduction label: partial-repro.
• No pull request: making private screenshots load requires verification and an access-preserving delivery design; that crosses the rule's simple-fix boundary.