Design a session-level fork / revert / recover / suspend mechanism over a paginated history with lineage tracking, immutable segments, global lock, ModelContext reconstruction, and bounded replay.
USE WHEN: designing session persistence, building a "fork this conversation" feature, building "undo last N turns", building "suspend and resume later", implementing a paginated history with segment-level cursor, reconstructing ModelContext from disk, or any task involving "session as a git-like object graph".
TRIGGER PHRASES: "session fork", "session branch", "thread fork", "thread rollback", "revert thread", "ThreadRollback", "SuspendTurnAndShutdown", "Op::RecoverTurn", "pagin…
