Two fixes for Google Chat reliability:
1. Space Events Response (Fixes 'Can't handle app response' error):
- Return proper JSON response for non-MESSAGE events in groups
- Handles ADDED_TO_SPACE, REMOVED_FROM_SPACE, etc.
- Previously returned empty '{}' which caused errors
2. Thread Reply Context (Adds missing context):
- Add threadReply field to GoogleChatMessage type
- Add quotedMessageMetadata field for quoted messages
- Pass IsThreadReply and QuotedMessageId to agent context
- Agent now knows when a message is a reply vs root message
Both fixes improve Google Chat reliability and agent context awareness.
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