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/golang.org/x/sys/windows/zsyscall_windows.go

@@ -511,6 +511,7 @@ var (
 	procFreeAddrInfoW                                        = modws2_32.NewProc("FreeAddrInfoW")
 	procGetAddrInfoW                                         = modws2_32.NewProc("GetAddrInfoW")
 	procWSACleanup                                           = modws2_32.NewProc("WSACleanup")
+	procWSADuplicateSocketW                                  = modws2_32.NewProc("WSADuplicateSocketW")
 	procWSAEnumProtocolsW                                    = modws2_32.NewProc("WSAEnumProtocolsW")
 	procWSAGetOverlappedResult                               = modws2_32.NewProc("WSAGetOverlappedResult")
 	procWSAIoctl                                             = modws2_32.NewProc("WSAIoctl")
@@ -4391,6 +4392,14 @@ func WSACleanup() (err error) {
 	return
 }
 
+func WSADuplicateSocket(s Handle, processID uint32, info *WSAProtocolInfo) (err error) {
+	r1, _, e1 := syscall.Syscall(procWSADuplicateSocketW.Addr(), 3, uintptr(s), uintptr(processID), uintptr(unsafe.Pointer(info)))
+	if r1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
 func WSAEnumProtocols(protocols *int32, protocolBuffer *WSAProtocolInfo, bufferLength *uint32) (n int32, err error) {
 	r0, _, e1 := syscall.Syscall(procWSAEnumProtocolsW.Addr(), 3, uintptr(unsafe.Pointer(protocols)), uintptr(unsafe.Pointer(protocolBuffer)), uintptr(unsafe.Pointer(bufferLength)))
 	n = int32(r0)