January 2026 monthly summary for martinvonz/jj. Key feature delivered: tree entries in the diff stream for directory change detection (VFS support). This adds the ability to include tree entries in the diff stream, enabling detection of changes within directories. It introduces diff_stream_with_trees and updates diff_stream_internal to support an optional flag for including tree objects, improving granularity for virtual file systems. The change provides better visibility into inner-directory changes, supporting more precise cache invalidation and synchronization workflows. No major bugs fixed this month. Overall impact: improved change-detection granularity translates into reduced unnecessary recomputation, faster incremental updates, and better consistency for VFS-backed clients. Technologies/skills demonstrated: diff streaming architecture, feature flag design, incremental refactoring, maintainable commit messaging, and traceability to a specific change (commit 1c5ce2bdee385106126260adce880f94c47e6606).