Preserve fenced Markdown blocks across message splits

[Copilot]

Long posts split mid-fenced code block, causing subsequent chunks to render as malformed Markdown. This preserves code-block formatting for each generated Mattermost message.

• Fenced code continuity

  • Close active ```/~~~ blocks at a chunk boundary.
  • Reopen the original fence, including its language hint, in the next chunk.

• Message numbering

  • Place sequence indicators on their own line before chunks that begin with a fence.

```json
{ "large": "payload" }

becomes independently rendered chunks with balanced fences.

<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes #10

[PromoFaux]

@copilot CI config has been fixed - please rebase on master

[Copilot]

@copilot CI config has been fixed - please rebase on master

Merged master in 58226c5.

[PromoFaux]

@copilot I don't currently have the ability to download and test this - but would love to see some screenshots or examples of this in action (adding markdown directly here may cause issues....)

[Copilot]

@copilot I don't currently have the ability to download and test this - but would love to see some screenshots or examples of this in action (adding markdown directly here may cause issues....)

The focused example is in Matterhook.NET.MatterhookClient.Tests/MiscTests.cs lines 25–34. A 25-character split of one json fenced block produces three independently valid messages: each boundary closes the prior fence and the continuation starts by reopening json; the final chunk contains the original closing fence and trailing text. This prevents the code-block formatting bleed shown in the supplied image.

[PromoFaux]

@copilot It might also be worth rolling in here an option to truncate rather than split, too. So that the end user has the ability to decide what they see

[Copilot]

@copilot It might also be worth rolling in here an option to truncate rather than split, too. So that the end user has the ability to decide what they see

Implemented in 8b27d53. PostAsync now accepts truncate: true, which sends only the first balanced chunk for both message and attachment text; the default continues splitting.