OMP session persistence, fork & tree: entry model, parent chains, /tree navigation, how navigateTree cuts leaf back to old branches
omp stores sessions as append-only JSONL with id/parentId forming a tree; a mutable leaf pointer selects the active path. /tree uses TreeSelectorComponent for navigation; navigateTree() switches leaf with optional branch summary, handles checkpoint/rewind, supports Claude/Codex foreign session import. Fork duplicates the session file inheriting providerPromptCacheKey. Resume/switchSession uses captureState/rollback for atomic transitions. Three-layer storage (indexed/history/artifact) separates concerns.