PR #1358 added the client-side lineage collapse helper, but
/api/sessions often did not include _lineage_root_id for the WebUI
JSON sessions visible in the sidebar. In that case the helper has no
grouping key and multiple same-title continuation rows remain visible.
This PR:
- Reads parent_session_id and end_reason from state.db.sessions for
the WebUI sidebar's session ids
- Walks the parent chain when end_reason is 'compression' or
'cli_close', producing _lineage_root_id and _compression_segment_count
- Cycle-detects via a 'seen' set
- Preserves projected lineage metadata on imported/gateway session rows
- Allows sidebar collapse to group cross-surface continuation chains
(CLI-close → WebUI continuation) while keeping non-continuation
parent rows flat
Co-authored-by: Dennis Soong <dso2ng@gmail.com>
7da1e074e4