Search Gmail for a thread to attach to the task [write]

Searches the caller's own Gmail connection, or a Gmail connection a teammate shared with the task's workspace, with Gmail's search syntax (q, e.g. from:supplier@example.com invoice). At most 10 threads. Read-only on Gmail. Write scope because each Gmail read is a billed connector call. Needs a person's own credential (403 person_required for a workspace key, an app or a task pass) and the right to send the task's first session messages (404 otherwise, as for an unknown task); 404 not_connected when there is no Gmail connection to read through; the workspace's tool-call rules apply (403 capability_denied).