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/internal/impl/codec_map.go

@@ -9,6 +9,7 @@ import (
 	"sort"
 
 	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/internal/errors"
 	"google.golang.org/protobuf/internal/genid"
 	"google.golang.org/protobuf/reflect/protoreflect"
 )
@@ -240,11 +241,16 @@ func appendMapItem(b []byte, keyrv, valrv reflect.Value, mapi *mapInfo, f *coder
 		size += mapi.keyFuncs.size(key.Value(), mapKeyTagSize, opts)
 		size += mapi.valFuncs.size(val, mapValTagSize, opts)
 		b = protowire.AppendVarint(b, uint64(size))
+		before := len(b)
 		b, err := mapi.keyFuncs.marshal(b, key.Value(), mapi.keyWiretag, opts)
 		if err != nil {
 			return nil, err
 		}
-		return mapi.valFuncs.marshal(b, val, mapi.valWiretag, opts)
+		b, err = mapi.valFuncs.marshal(b, val, mapi.valWiretag, opts)
+		if measuredSize := len(b) - before; size != measuredSize && err == nil {
+			return nil, errors.MismatchedSizeCalculation(size, measuredSize)
+		}
+		return b, err
 	} else {
 		key := mapi.conv.keyConv.PBValueOf(keyrv).MapKey()
 		val := pointerOfValue(valrv)
@@ -259,7 +265,12 @@ func appendMapItem(b []byte, keyrv, valrv reflect.Value, mapi *mapInfo, f *coder
 		}
 		b = protowire.AppendVarint(b, mapi.valWiretag)
 		b = protowire.AppendVarint(b, uint64(valSize))
-		return f.mi.marshalAppendPointer(b, val, opts)
+		before := len(b)
+		b, err = f.mi.marshalAppendPointer(b, val, opts)
+		if measuredSize := len(b) - before; valSize != measuredSize && err == nil {
+			return nil, errors.MismatchedSizeCalculation(valSize, measuredSize)
+		}
+		return b, err
 	}
 }