The room-level test is the reported defect: two composer sends, two
threads, and neither backend transcript may contain the other thread's
prompt. Proven red on the unfixed code — both threads resolved to
sid-research-1.
Also pins same-thread continuity, the pre-thread adoption (first thread
continues the old conversation, later threads do not), and that the
member half of the key stays source-qualified so a remote `research` and
a local `research` never share a session.
Co-authored-by: Wenfengcheng <30426178+Wenfengcheng@users.noreply.github.com>
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