Why: parallel conversations in one project cannot see each other's
transcripts, which already caused duplicate delivery of the same
requirement (records/2026-09-30-lesson-parallel-session-duplication.md);
artifacts/knowledge are already project-shared, so transcripts are the
only missing channel.
Evidence: permission formula and gate matrix designed fail-closed
(project switch default off; per-conversation outbound/inbound flags
default open/shared); tool design lands the "conversation history
search" builtin planned in skeleton design 4.8.
Impact: documents only; implementation follows in core/backend/frontend
under Dev task feature/cross-session-reading.
Refs: proposals/2026-09-29-system-skeleton-design-and-plan.md 4.8/4.9;
records/2026-09-30-lesson-parallel-session-duplication.md.
weichen
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