List every activity sharing the given activity's Nylas thread id.
Activity
Get activity thread
Scoped to the caller’s tenant (via tenant_uuid) to prevent
cross-tenant thread spills. Only EMAIL activities are returned —
calendar events share thread_id=None semantics and would muddy
the result set.
The response is metadata-only. Clients render a thread by fetching
this list and then calling /activities/{id}/body for whichever
messages they want to expand.
GET
List every activity sharing the given activity's Nylas thread id.