Summary

When sending Markdown through the built-in Mattermost channel plugin, several block-level Markdown constructs are degraded into plain text (or otherwise lose formatting). Mattermost itself supports these constructs when the same Markdown is pasted directly into the client.

Affected constructs

• Headings (#, ##, ###) render as plain text
• Blockquotes (>) render as plain text
• Lists (nested - and 1.) lose structure/indentation
• Task lists (- [ ], - [x]) render as literal text, not checkboxes

Steps to reproduce

Send this message via OpenClaw → Mattermost:

# H1
## H2

> quoted line
> second line

- item A
- item B
  - sub B1

- [ ] todo
- [x] done

1. first
2. second
   1. second.1

Expected behavior

Mattermost should render the message with headings, quote styling, properly nested lists, and task list checkboxes (same behavior as when pasting the Markdown directly into Mattermost).

Actual behavior

These constructs are rendered as plain text / flattened content.

Environment

• Mattermost clients tested: Web, Desktop (Linux), Android

Notes

This suggests the OpenClaw Markdown → IR → channel renderer path is stripping or over-sanitizing block nodes for Mattermost. A Mattermost-specific renderer or a “send raw Markdown” option may be needed.