| Pack files | Chunks grouped into ~32 MiB packs with dynamic sizing, separate data/tree packs |
| Retention policies | keep_daily, keep_weekly, keep_monthly, keep_yearly, keep_last, keep_within |
| snapshot delete command | Remove individual snapshots, decrement refcounts |
| prune command | Apply retention policies, remove expired snapshots |
| check command | Structural integrity + optional --verify-data for full content verification |
| Type-safe PackId | Newtype for pack file identifiers with storage_key() |
| compact command | Rewrite packs to reclaim space from orphaned blobs after delete/prune |
| REST server | axum-based backup server with auth, append-only enforcement, quotas, freshness tracking, and server-side compaction |
| REST backend | StorageBackend over HTTP with range-read support |
| Tiered dedup index | Backup dedup via session map + xor filter + mmap dedup cache, with safe fallback to HashMap dedup mode |
| Restore mmap cache | Restore-cache-first item-stream lookup with safe fallback to the full index when cache entries are stale or incomplete |
| Append-only repository layout v2 | Snapshot listing derived from immutable snapshots/<id> blobs; index stores authenticated generation and index.gen is an advisory cache hint |
| Bounded parallel pipeline | Byte-budgeted pipeline with bounded worker/upload concurrency derived from limits.threads and limits.connections |
| Heap-backed pack assembly | Pack writers use heap-backed buffers after the mmap path was removed for reliability on some systems |
| cache_dir override | Configurable root for file cache, dedup/restore/full-index caches, and preferred mmap temp-file location |
| Parallel transforms | rayon-backed compression/encryption within the bounded pipeline |
| break-lock command | Forced stale-lock cleanup for backend/object lock recovery |
| Compact pack health accounting | Compact analysis reports/tracks corrupt and orphan packs in addition to reclaimable dead bytes |
| File-level cache | inode/mtime/ctime skip for unchanged files — avoids read, chunk, compress, encrypt. Keys are 16-byte BLAKE2b path hashes (with transparent legacy migration). Stored locally under the per-repo cache root (default platform cache dir + vykar, or cache_dir override). |
| Daemon mode | vykar daemon runs scheduled backup→prune→compact→check cycles with two-stage signal handling |
| Server-side pack verification | vykar check delegates pack integrity checks to vykar-server when available; --distrust-server opts out |
| Upload integrity | REST PUT includes X-Content-BLAKE2b header; server verifies during streaming write |
| vykar-protocol crate | Shared wire-format types and pack/protocol version constants between client and server |
| Type-safe SnapshotId | Newtype for snapshot identifiers with storage_key() for snapshots/<id> objects |