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/unix/syscall_linux.go

@@ -13,6 +13,7 @@ package unix
 
 import (
 	"encoding/binary"
+	"slices"
 	"strconv"
 	"syscall"
 	"time"
@@ -417,7 +418,7 @@ func (sa *SockaddrUnix) sockaddr() (unsafe.Pointer, _Socklen, error) {
 		return nil, 0, EINVAL
 	}
 	sa.raw.Family = AF_UNIX
-	for i := 0; i < n; i++ {
+	for i := range n {
 		sa.raw.Path[i] = int8(name[i])
 	}
 	// length is family (uint16), name, NUL.
@@ -507,7 +508,7 @@ func (sa *SockaddrL2) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	psm := (*[2]byte)(unsafe.Pointer(&sa.raw.Psm))
 	psm[0] = byte(sa.PSM)
 	psm[1] = byte(sa.PSM >> 8)
-	for i := 0; i < len(sa.Addr); i++ {
+	for i := range len(sa.Addr) {
 		sa.raw.Bdaddr[i] = sa.Addr[len(sa.Addr)-1-i]
 	}
 	cid := (*[2]byte)(unsafe.Pointer(&sa.raw.Cid))
@@ -589,11 +590,11 @@ func (sa *SockaddrCAN) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Family = AF_CAN
 	sa.raw.Ifindex = int32(sa.Ifindex)
 	rx := (*[4]byte)(unsafe.Pointer(&sa.RxID))
-	for i := 0; i < 4; i++ {
+	for i := range 4 {
 		sa.raw.Addr[i] = rx[i]
 	}
 	tx := (*[4]byte)(unsafe.Pointer(&sa.TxID))
-	for i := 0; i < 4; i++ {
+	for i := range 4 {
 		sa.raw.Addr[i+4] = tx[i]
 	}
 	return unsafe.Pointer(&sa.raw), SizeofSockaddrCAN, nil
@@ -618,11 +619,11 @@ func (sa *SockaddrCANJ1939) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	sa.raw.Family = AF_CAN
 	sa.raw.Ifindex = int32(sa.Ifindex)
 	n := (*[8]byte)(unsafe.Pointer(&sa.Name))
-	for i := 0; i < 8; i++ {
+	for i := range 8 {
 		sa.raw.Addr[i] = n[i]
 	}
 	p := (*[4]byte)(unsafe.Pointer(&sa.PGN))
-	for i := 0; i < 4; i++ {
+	for i := range 4 {
 		sa.raw.Addr[i+8] = p[i]
 	}
 	sa.raw.Addr[12] = sa.Addr
@@ -911,7 +912,7 @@ func (sa *SockaddrIUCV) sockaddr() (unsafe.Pointer, _Socklen, error) {
 	// These are EBCDIC encoded by the kernel, but we still need to pad them
 	// with blanks. Initializing with blanks allows the caller to feed in either
 	// a padded or an unpadded string.
-	for i := 0; i < 8; i++ {
+	for i := range 8 {
 		sa.raw.Nodeid[i] = ' '
 		sa.raw.User_id[i] = ' '
 		sa.raw.Name[i] = ' '
@@ -1148,7 +1149,7 @@ func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
 		var user [8]byte
 		var name [8]byte
 
-		for i := 0; i < 8; i++ {
+		for i := range 8 {
 			user[i] = byte(pp.User_id[i])
 			name[i] = byte(pp.Name[i])
 		}
@@ -1173,11 +1174,11 @@ func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
 				Ifindex: int(pp.Ifindex),
 			}
 			name := (*[8]byte)(unsafe.Pointer(&sa.Name))
-			for i := 0; i < 8; i++ {
+			for i := range 8 {
 				name[i] = pp.Addr[i]
 			}
 			pgn := (*[4]byte)(unsafe.Pointer(&sa.PGN))
-			for i := 0; i < 4; i++ {
+			for i := range 4 {
 				pgn[i] = pp.Addr[i+8]
 			}
 			addr := (*[1]byte)(unsafe.Pointer(&sa.Addr))
@@ -1188,11 +1189,11 @@ func anyToSockaddr(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
 				Ifindex: int(pp.Ifindex),
 			}
 			rx := (*[4]byte)(unsafe.Pointer(&sa.RxID))
-			for i := 0; i < 4; i++ {
+			for i := range 4 {
 				rx[i] = pp.Addr[i]
 			}
 			tx := (*[4]byte)(unsafe.Pointer(&sa.TxID))
-			for i := 0; i < 4; i++ {
+			for i := range 4 {
 				tx[i] = pp.Addr[i+4]
 			}
 			return sa, nil
@@ -2216,10 +2217,7 @@ func readvRacedetect(iovecs []Iovec, n int, err error) {
 		return
 	}
 	for i := 0; n > 0 && i < len(iovecs); i++ {
-		m := int(iovecs[i].Len)
-		if m > n {
-			m = n
-		}
+		m := min(int(iovecs[i].Len), n)
 		n -= m
 		if m > 0 {
 			raceWriteRange(unsafe.Pointer(iovecs[i].Base), m)
@@ -2270,10 +2268,7 @@ func writevRacedetect(iovecs []Iovec, n int) {
 		return
 	}
 	for i := 0; n > 0 && i < len(iovecs); i++ {
-		m := int(iovecs[i].Len)
-		if m > n {
-			m = n
-		}
+		m := min(int(iovecs[i].Len), n)
 		n -= m
 		if m > 0 {
 			raceReadRange(unsafe.Pointer(iovecs[i].Base), m)
@@ -2320,12 +2315,7 @@ func isGroupMember(gid int) bool {
 		return false
 	}
 
-	for _, g := range groups {
-		if g == gid {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(groups, gid)
 }
 
 func isCapDacOverrideSet() bool {