migrate_memory_files() uploads USER.md/MEMORY.md with peer=user_peer — the
session's runtime user. In shared channels, a non-owner's new thread uploads
the owner's full profile under the NON-OWNER's peer; Honcho's deriver then
attributes the owner's psychometrics/medical/biography to that person. This
was the root contamination vector (55/70 contaminated sessions carried the
payload). Skip migration unless the session user is the configured owner.
SOUL.md unaffected (uploads under assistant peer).
Co-authored-by: Minh Nguyen <menhguin@users.noreply.github.com>
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