Session resume now tracks transcript lineages, a rewound flag, and class-filtered message keys

What

• The structure that tracks which retained or forked messages ('keys') belong to a session now also carries transcriptLineages and a keysWithClass subset (messages meeting a class predicate), plus a rewound flag, where before it only tracked a plain list of keys.
• The session-resume helpers now build these richer objects from a shared empty-state constructor.
• Resume logic no longer just scans for the first turn not already held; it now classifies turns as 'fresh' or 'withClass' and picks the resume point using that classification.

Why

This gives Claude Code more precise bookkeeping when resuming a session, including whether the session was rewound and which messages match particular criteria, so resume picks up from the right point more reliably.