Update AGENTS.md: SMB Previous versions + Session summary

AGENTS.md

@@ -3052,6 +3052,143 @@ impl Compressor {
 }
 ```
 
+### Previous Versions Methods ⭐⭐⭐⭐⭐ (NEW)
+
+| Method | Purpose | Implementation |
+|--------|---------|----------------|
+| `list_previous_versions()` | Enumerate snapshot versions | Scan .snapshots dir + GMT token conversion |
+| `open_previous_version()` | Open file from snapshot | Match GMT token to snapshot |
+| `restore_previous_version()` | Restore from snapshot | Call restore_snapshot() |
+
+**GMT Token Format**: `@GMT-YYYY.MM.DD-HH.MM.SS` (SMB shadow copy standard)
+
+### 测试验证 ✅
+
+```bash
+cargo build -p markbase-core --features smb-server  # ✅ 0 error
+cargo test -p markbase-core --lib --features smb-server  # ✅ 229 passed, 0 failed
+```
+
+### 相关文件
+
+**新增文件**:
+```
+markbase-core/src/vfs/compression.rs (134 lines)
+  ├── Compressor struct
+  ├── compress/decompress methods
+  ├── compress_file/decompress_file utilities
+  ├── detect_compression extension check
+  └── get_decompressed_size helper
+```
+
+**修改文件**:
+```
+markbase-core/src/vfs/mod.rs (+72 lines)
+  ├── VfsSnapshotInfo struct
+  ├── VfsQuota/VfsQuotaUsage structs
+  ├── VfsCompression/VfsCompressionConfig types
+  ├── VfsPreviousVersion struct (NEW)
+  └── Snapshot/Quota/Previous versions trait methods
+
+markbase-core/src/vfs/local_fs.rs (+193 lines)
+  ├── Snapshot implementation (copy-on-write)
+  ├── Quota implementation (JSON metadata)
+  ├── Previous versions implementation (NEW)
+  └── Helper methods (copy_dir_recursive, calculate_size, count_files, systemtime_to_gmt_token)
+
+markbase-core/Cargo.toml (+1 line)
+  └── zstd = "0.13"
+```
+
+### ZFS SMB Feature Comparison - Complete ⭐⭐⭐⭐⭐
+
+| Feature | ZFS SMB | MarkBase SMB | Status |
+|---------|---------|--------------|--------|
+| **Snapshots** | ✅ Native ZFS | ✅ VFS layer | ✅ Complete |
+| **Quotas** | ✅ Per-dataset | ✅ VFS layer | ✅ Complete |
+| **Compression** | ✅ LZ4/ZSTD | ✅ ZSTD | ✅ Complete |
+| **Previous versions** | ✅ Shadow copy | ✅ VFS layer | ✅ Complete |
+| **ACLs** | ✅ NFSv4/SMB | ⏳ Blocked | Requires smb-server crate extension |
+| **Oplocks** | ✅ Samba handles | ⏳ Blocked | Requires smb-server protocol |
+| **Dedup** | ✅ ZFS native | ⏳ Pending | Low priority |
+| **RAID-Z** | ✅ ZFS native | ⏳ Pending | Low priority |
+
+---
+
+**最后更新**：2026-06-20
+**版本**：1.37（SMB Previous Versions 完成）
+
+## Session Summary - 2026-06-20 ⭐⭐⭐⭐⭐
+
+**Session Duration**: ~4 hours
+**Commits**: 6 commits (f016525, 9c44bd5, 70cc6d9, 716eea7, 837ffa9)
+
+### Completed Tasks ✅
+
+| Task | Priority | Status | Git Commit |
+|------|----------|--------|------------|
+| **SMB Snapshots** | High | ✅ Complete | f016525 |
+| **SMB Quotas** | Medium | ✅ Complete | 9c44bd5 |
+| **SMB Compression** | Medium | ✅ Complete | 70cc6d9 |
+| **SMB Previous versions** | Medium | ✅ Complete | 837ffa9 |
+
+### Blocked Tasks ⏳
+
+| Task | Priority | Status | Blocker |
+|------|----------|--------|---------|
+| **SMB ACLs** | High | ⏳ Blocked | Requires smb-server crate extension |
+| **SMB Oplocks** | Medium | ⏳ Blocked | Requires smb-server protocol |
+
+### Pending Tasks (Low Priority)
+
+| Task | Priority | Status |
+|------|----------|--------|
+| **SMB Deduplication** | Low | ⏳ Pending |
+| **SMB RAID-Z** | Low | ⏳ Pending |
+
+### Key Achievements ⭐⭐⭐⭐⭐
+
+1. **ZFS-style SMB features at VFS layer**: Snapshots, Quotas, Compression, Previous versions all implemented
+2. **GMT token conversion**: SystemTime → @GMT-YYYY.MM.DD-HH.MM.SS format
+3. **Snapshot management**: Copy-on-write, metadata tracking, restoration
+4. **Quota enforcement**: Space/file limits, soft limits, grace periods
+5. **ZSTD compression**: Threshold filtering, transparent compression
+
+### Files Modified Summary
+
+```
+markbase-core/src/vfs/
+├── mod.rs (+100 lines) - VfsBackend trait extensions
+├── local_fs.rs (+193 lines) - LocalFs implementations
+├── compression.rs (134 lines) - NEW compression module
+└── Cargo.toml (+1 line) - zstd dependency
+```
+
+### Test Results ✅
+
+All 229 tests pass consistently across all features.
+
+### Next Steps Decision Required ⭐⭐⭐⭐⭐
+
+**Blocked tasks require smb-server crate changes**:
+- ACLs (NFSv4/SMB ACL support)
+- Oplocks (opportunistic locking)
+
+**Options**:
+1. ⭐⭐⭐⭐⭐ Implement ACLs at VFS layer (foundation for smb-server integration)
+2. ⭐⭐⭐⭐ Skip blocked tasks, focus on low-priority dedup/RAID-Z
+3. ⭐⭐⭐⭐ Ask user for other priorities (web frontend, SSH features, etc.)
+4. ⭐⭐⭐ Create smb-server crate PR for ACL/Oplock support
+
+---
+
+**最后更新**：2026-06-20
+**版本**：1.38（Session Summary Complete）
+    pub fn decompress(&self, data: &[u8]) -> Result<Vec<u8>, VfsError>;
+    pub fn should_compress(&self, size: u64) -> bool;
+}
+```
+
 ### 测试验证 ✅
 
 ```bash