The idle sweep archives a whole compression lineage. When the chat later
resumed and compressed, the new tip was inserted with archived=0 under the
archived root, and the sidebar admits a lineage by its root's flag, so the
live chat stayed hidden.
Record sweep provenance in a new sessions.auto_archived column. Publishing a
compression child or reopening a session under a sweep-only archive
un-hides the lineage; a deliberate archive (sidebar, API, CLI) clears the
provenance and keeps the chat hidden. Compression children now inherit the
parent's archive state so a manually archived lineage stays uniform.
Fixes#117713
6397a84a91