When native slash commands are executed in Telegram topics/forums, the
originating topic context was not being preserved. This caused sub-agent
announcements to be delivered to the wrong topic.
Root cause: Native slash command context did not set OriginatingChannel
and OriginatingTo, causing session delivery context to fallback to the
user's personal ID instead of the group ID + topic.
Fix: Added OriginatingChannel and OriginatingTo to native slash command
context, ensuring topic information is preserved for sub-agent announcements.
Related session fields:
- lastThreadId: preserved via MessageThreadId
- lastTo: now correctly set to group ID via OriginatingTo
- deliveryContext: includes threadId for proper routing
