Phase 2: Implement Execution Environment Abstraction (v0.3.0)

This commit implements Phase 2 of the CHORUS Task Execution Engine development plan,
providing a comprehensive execution environment abstraction layer with Docker
container sandboxing support.

## New Features

### Core Sandbox Interface
- Comprehensive ExecutionSandbox interface with isolated task execution
- Support for command execution, file I/O, environment management
- Resource usage monitoring and sandbox lifecycle management
- Standardized error handling with SandboxError types and categories

### Docker Container Sandbox Implementation
- Full Docker API integration with secure container creation
- Transparent repository mounting with configurable read/write access
- Advanced security policies with capability dropping and privilege controls
- Comprehensive resource limits (CPU, memory, disk, processes, file handles)
- Support for tmpfs mounts, masked paths, and read-only bind mounts
- Container lifecycle management with proper cleanup and health monitoring

### Security & Resource Management
- Configurable security policies with SELinux, AppArmor, and Seccomp support
- Fine-grained capability management with secure defaults
- Network isolation options with configurable DNS and proxy settings
- Resource monitoring with real-time CPU, memory, and network usage tracking
- Comprehensive ulimits configuration for process and file handle limits

### Repository Integration
- Seamless repository mounting from local paths to container workspaces
- Git configuration support with user credentials and global settings
- File inclusion/exclusion patterns for selective repository access
- Configurable permissions and ownership for mounted repositories

### Testing Infrastructure
- Comprehensive test suite with 60+ test cases covering all functionality
- Docker integration tests with Alpine Linux containers (skipped in short mode)
- Mock sandbox implementation for unit testing without Docker dependencies
- Security policy validation tests with read-only filesystem enforcement
- Resource usage monitoring and cleanup verification tests

## Technical Details

### Dependencies Added
- github.com/docker/docker v28.4.0+incompatible - Docker API client
- github.com/docker/go-connections v0.6.0 - Docker connection utilities
- github.com/docker/go-units v0.5.0 - Docker units and formatting
- Associated Docker API dependencies for complete container management

### Architecture
- Interface-driven design enabling multiple sandbox implementations
- Comprehensive configuration structures for all sandbox aspects
- Resource usage tracking with detailed metrics collection
- Error handling with retryable error classification
- Proper cleanup and resource management throughout sandbox lifecycle

### Compatibility
- Maintains backward compatibility with existing CHORUS architecture
- Designed for future integration with Phase 3 Core Task Execution Engine
- Extensible design supporting additional sandbox implementations (VM, process)

This Phase 2 implementation provides the foundation for secure, isolated task
execution that will be integrated with the AI model providers from Phase 1
in the upcoming Phase 3 development.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

vendor/github.com/Microsoft/go-winio/fileinfo.go

@@ -0,0 +1,106 @@
+//go:build windows
+// +build windows
+
+package winio
+
+import (
+	"os"
+	"runtime"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// FileBasicInfo contains file access time and file attributes information.
+type FileBasicInfo struct {
+	CreationTime, LastAccessTime, LastWriteTime, ChangeTime windows.Filetime
+	FileAttributes                                          uint32
+	_                                                       uint32 // padding
+}
+
+// alignedFileBasicInfo is a FileBasicInfo, but aligned to uint64 by containing
+// uint64 rather than windows.Filetime. Filetime contains two uint32s. uint64
+// alignment is necessary to pass this as FILE_BASIC_INFO.
+type alignedFileBasicInfo struct {
+	CreationTime, LastAccessTime, LastWriteTime, ChangeTime uint64
+	FileAttributes                                          uint32
+	_                                                       uint32 // padding
+}
+
+// GetFileBasicInfo retrieves times and attributes for a file.
+func GetFileBasicInfo(f *os.File) (*FileBasicInfo, error) {
+	bi := &alignedFileBasicInfo{}
+	if err := windows.GetFileInformationByHandleEx(
+		windows.Handle(f.Fd()),
+		windows.FileBasicInfo,
+		(*byte)(unsafe.Pointer(bi)),
+		uint32(unsafe.Sizeof(*bi)),
+	); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	// Reinterpret the alignedFileBasicInfo as a FileBasicInfo so it matches the
+	// public API of this module. The data may be unnecessarily aligned.
+	return (*FileBasicInfo)(unsafe.Pointer(bi)), nil
+}
+
+// SetFileBasicInfo sets times and attributes for a file.
+func SetFileBasicInfo(f *os.File, bi *FileBasicInfo) error {
+	// Create an alignedFileBasicInfo based on a FileBasicInfo. The copy is
+	// suitable to pass to GetFileInformationByHandleEx.
+	biAligned := *(*alignedFileBasicInfo)(unsafe.Pointer(bi))
+	if err := windows.SetFileInformationByHandle(
+		windows.Handle(f.Fd()),
+		windows.FileBasicInfo,
+		(*byte)(unsafe.Pointer(&biAligned)),
+		uint32(unsafe.Sizeof(biAligned)),
+	); err != nil {
+		return &os.PathError{Op: "SetFileInformationByHandle", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return nil
+}
+
+// FileStandardInfo contains extended information for the file.
+// FILE_STANDARD_INFO in WinBase.h
+// https://docs.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-file_standard_info
+type FileStandardInfo struct {
+	AllocationSize, EndOfFile int64
+	NumberOfLinks             uint32
+	DeletePending, Directory  bool
+}
+
+// GetFileStandardInfo retrieves ended information for the file.
+func GetFileStandardInfo(f *os.File) (*FileStandardInfo, error) {
+	si := &FileStandardInfo{}
+	if err := windows.GetFileInformationByHandleEx(windows.Handle(f.Fd()),
+		windows.FileStandardInfo,
+		(*byte)(unsafe.Pointer(si)),
+		uint32(unsafe.Sizeof(*si))); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return si, nil
+}
+
+// FileIDInfo contains the volume serial number and file ID for a file. This pair should be
+// unique on a system.
+type FileIDInfo struct {
+	VolumeSerialNumber uint64
+	FileID             [16]byte
+}
+
+// GetFileID retrieves the unique (volume, file ID) pair for a file.
+func GetFileID(f *os.File) (*FileIDInfo, error) {
+	fileID := &FileIDInfo{}
+	if err := windows.GetFileInformationByHandleEx(
+		windows.Handle(f.Fd()),
+		windows.FileIdInfo,
+		(*byte)(unsafe.Pointer(fileID)),
+		uint32(unsafe.Sizeof(*fileID)),
+	); err != nil {
+		return nil, &os.PathError{Op: "GetFileInformationByHandleEx", Path: f.Name(), Err: err}
+	}
+	runtime.KeepAlive(f)
+	return fileID, nil
+}