The liveChatId fix (TASK 44) worked on the next Test Stream, but every Mock
Chat Input send returned 'YouTube rejected the message (error 400)'. The
runtime log's body: 400 MISSING_REQUIRED_FIELD, domain
youtube.api.v3.LiveChatMessageInsertResponse.Error.
The liveChat/messages.insert snippet requires type ('textMessageEvent' or
'pollEvent') alongside liveChatId and textMessageDetails.messageText; the
TASK 41 body omitted it, and the Good Dog test asserted only liveChatId +
messageText were present — false-green while real YouTube rejected every
send. Fix body + assert type in the same test so the field can never drop
silently again.
Reference: https://developers.google.com/youtube/v3/live/docs/liveChatMessages/insert
Good Dog: ONE integration test (strengthened TestStream_DockTooling...).
Gate: clean build 0 warnings; full vstest 317/318 (the 1 failure is the
known environmental RealMouseDrag flake — passes 3/3 in isolation).
