Enumerated every /api/session/<mutation> route and applied _session_is_subagent_view_only:
duplicate, branch, retry, undo, toolsets, compress, archive (existing-sidecar path)
now 400 for subagent children; delete/clear/truncate/pin already gated; rename/move/update
route through the gated _get_or_materialize_session (403). This closes the data-loss
paths (delete_cli_session, retry/undo truncate, branch/duplicate fork).
Also: /api/sessions list coercion now also honors state.db source='subagent' for rows
whose stale index says webui/fork, so they can't surface as writable/CLI sidebar rows.
Fixes#5307
nesquena-hermes
e6e7454c7a