Summary

• Adds remend to fix broken markdown rendering during fallback streaming (Teams, GChat, Discord)
• Remend is the markdown healing library that powers Streamdown — it intelligently closes dangling markdown syntax (**bold, ```code, [links](, etc.) in real-time as tokens stream in
• Applied to intermediate edits only — the final message uses raw accumulated text since it's already complete
• Wraps streamed message content in { markdown: string } objects instead of plain strings, giving adapters explicit format context for both postMessage, editMessage, and stream calls
• Slack is unaffected (uses native streaming API)

What was happening

During fallback streaming, intermediate edits are sent every 500ms with whatever text has accumulated so far. If the AI is mid-stream through a markdown construct like **bold, the user sees broken formatting until the closing syntax arrives.

Additionally, adapters had no way to distinguish between plain text and markdown content — wrapping in { markdown: string } makes the format explicit.

Test plan

• Added test verifying intermediate edits have balanced markdown markers
• Updated all streaming tests to expect { markdown: string } content format
• All existing streaming tests pass
• Full validation passes (pnpm validate)