bug(confluence): markdown attachment images show "Preview unavailable" after update_page

[kbichave]

Summary

When using confluence_update_page with content_format="markdown", any image referencing a page attachment by filename (e.g. ![alt](figure.png)) is silently converted to a raw HTML <img> tag. Confluence cannot resolve bare filenames as page attachments, so every such image renders as "Preview unavailable" on the published page.

This is a silent data-corruption bug — the tool succeeds, returns no error, and the page looks fine in the API response. The breakage is only visible when a human opens the page.

Steps to reproduce

1. Attach an image (chart.png) to a Confluence page.
2. Call confluence_update_page with content_format="markdown" and content:

   ![Revenue chart](chart.png)

3. Open the page in Confluence → image slot shows "Preview unavailable".

Root cause

The markdown→storage conversion (via md2conf) emits:

<img alt="Revenue chart" src="chart.png"/>

Confluence Storage Format does not support <img src="..."> for page attachments. The correct representation is:

<ac:image ac:alt="Revenue chart">
  <ri:attachment ri:filename="chart.png"/>
</ac:image>

External URLs (src="https://...") render fine — only bare filenames and relative paths are affected.

Fix

Post-process the storage HTML from markdown_to_confluence_storage to replace bare-filename <img> tags with ac:image / ri:attachment macros. External URLs and absolute paths pass through unchanged.

I have a working fix with regression tests and will submit a PR linked to this issue.

[Troubladore]

Integrated into the community fork via Troubladore/mcp-atlassian#170. Applied as-is — clean fix, good tests.