Summary

In extensions/mattermost/src/mattermost/monitor.ts, the channelKind helper only special-cases "D" (direct) and "G" (group) channel types. Mattermost private channels, which use type "P", fall through to the default "channel" case and are treated as public channels.

Impact

Private channel messages are routed and handled as if they were public — potentially affecting groupPolicy, requireMention, and other access controls that behave differently for private vs public contexts.

Steps to reproduce

1. Configure a Mattermost account with access to a private channel (type P)
2. Send a message to the private channel
3. Observe it is processed with channelKind = "channel" instead of "private-channel" or similar

Suggested fix

Add a case for "P" in channelKind:

case "P":
  return "private-channel";

And ensure downstream routing/policy logic handles "private-channel" appropriately.

Version

Latest main (identified in extensions/mattermost/src/mattermost/monitor.ts)