Implement optional support for messages

- Handle throwing gracefuly
- Define strategies for either not showing part of the content, or showing unsupported message if part couldn't be build

Start by tracing the message-building and display entry points in Chatto, since the issue names no files or tests. Clarify how failures should be handled and choose between omitting unsupported content or showing an unsupported-message notice; done means the selected behavior is implemented and verified for both successful and unsupported messages.

Written by the indexing model from the issue text.