feat(rust-core): add zstd chunk compression support and rewrite partially referenced packs during prune

rust/src/restore.rs

@@ -10,7 +10,7 @@ use crate::encryption;
 use crate::error::ArchiveError;
 use crate::hasher;
 use crate::pack_reader;
-use crate::pack_writer::IdxEntry;
+use crate::pack_writer::{IdxEntry, FLAG_ENCRYPTED};
 use crate::repository::Repository;
 use crate::snapshot;
 
@@ -76,8 +76,15 @@ pub async fn restore(
                 index_entry.compressed_size,
             ).await?;
 
+            // Get flags for this chunk (determines compression algorithm)
+            let chunk_flags = index_entry.flags;
+
             // Decrypt if encrypted
-            let compressed = if let Some(ref key) = repo.master_key {
+            let compressed = if chunk_flags & FLAG_ENCRYPTED != 0 {
+                let key = repo.master_key.as_ref().ok_or_else(|| {
+                    ArchiveError::Encryption("Chunk is encrypted but no key available".to_string())
+                })?;
+
                 // Try to get nonce from the global index first (fast path)
                 let nonce = if let Some(ref nonce_hex) = index_entry.nonce {
                     let nonce_bytes = hex::decode(nonce_hex)
@@ -117,8 +124,8 @@ pub async fn restore(
                 stored_data
             };
 
-            // Decompress
-            let plaintext = compression::decompress(&compressed)?;
+            // Decompress using flags to determine algorithm
+            let plaintext = compression::decompress_by_flags(&compressed, chunk_flags)?;
 
             // Verify hash
             let actual_hash = hasher::hash_chunk(&plaintext);