release: 0.4.1b6

## Bump
- [ ] Major
- [ ] Minor
- [x] Beta
- [ ] Patch
- [ ] Skip

## Changelog

### Fixed
- Reset sync cursor on historic handoff so the sync handler no longer replays the entire backlog (#294)
- Sync-cursor handler opens `instances.sync()` in `no_backfill` mode when no saved cursor and no cutoff (forward-only)
- Avoid KeyError on post-reset empty cursor state

### Added
- Estate-wide edge existence baseline handler (`validation_type: edge_existence_baseline`) and orchestrator Step 3b (#290)
