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/google.golang.org/protobuf/reflect/protodesc/editions.go

@@ -17,11 +17,6 @@ import (
 	gofeaturespb "google.golang.org/protobuf/types/gofeaturespb"
 )
 
-const (
-	SupportedEditionsMinimum = descriptorpb.Edition_EDITION_PROTO2
-	SupportedEditionsMaximum = descriptorpb.Edition_EDITION_2023
-)
-
 var defaults = &descriptorpb.FeatureSetDefaults{}
 var defaultsCacheMu sync.Mutex
 var defaultsCache = make(map[filedesc.Edition]*descriptorpb.FeatureSet)
@@ -67,18 +62,20 @@ func getFeatureSetFor(ed filedesc.Edition) *descriptorpb.FeatureSet {
 		fmt.Fprintf(os.Stderr, "internal error: unsupported edition %v (did you forget to update the embedded defaults (i.e. the bootstrap descriptor proto)?)\n", edpb)
 		os.Exit(1)
 	}
-	fs := defaults.GetDefaults()[0].GetFeatures()
+	fsed := defaults.GetDefaults()[0]
 	// Using a linear search for now.
 	// Editions are guaranteed to be sorted and thus we could use a binary search.
 	// Given that there are only a handful of editions (with one more per year)
 	// there is not much reason to use a binary search.
 	for _, def := range defaults.GetDefaults() {
 		if def.GetEdition() <= edpb {
-			fs = def.GetFeatures()
+			fsed = def
 		} else {
 			break
 		}
 	}
+	fs := proto.Clone(fsed.GetFixedFeatures()).(*descriptorpb.FeatureSet)
+	proto.Merge(fs, fsed.GetOverridableFeatures())
 	defaultsCache[ed] = fs
 	return fs
 }