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/filedesc/desc_lazy.go

@@ -45,6 +45,11 @@ func (file *File) resolveMessages() {
 			case protoreflect.MessageKind, protoreflect.GroupKind:
 				fd.L1.Message = file.resolveMessageDependency(fd.L1.Message, listFieldDeps, depIdx)
 				depIdx++
+				if fd.L1.Kind == protoreflect.GroupKind && (fd.IsMap() || fd.IsMapEntry()) {
+					// A map field might inherit delimited encoding from a file-wide default feature.
+					// But maps never actually use delimited encoding. (At least for now...)
+					fd.L1.Kind = protoreflect.MessageKind
+				}
 			}
 
 			// Default is resolved here since it depends on Enum being resolved.
@@ -466,10 +471,10 @@ func (fd *Field) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd protoref
 			b = b[m:]
 		}
 	}
-	if fd.Syntax() == protoreflect.Editions && fd.L1.Kind == protoreflect.MessageKind && fd.L1.EditionFeatures.IsDelimitedEncoded {
+	if fd.L1.Kind == protoreflect.MessageKind && fd.L1.EditionFeatures.IsDelimitedEncoded {
 		fd.L1.Kind = protoreflect.GroupKind
 	}
-	if fd.Syntax() == protoreflect.Editions && fd.L1.EditionFeatures.IsLegacyRequired {
+	if fd.L1.EditionFeatures.IsLegacyRequired {
 		fd.L1.Cardinality = protoreflect.Required
 	}
 	if rawTypeName != nil {
@@ -496,13 +501,11 @@ func (fd *Field) unmarshalOptions(b []byte) {
 			b = b[m:]
 			switch num {
 			case genid.FieldOptions_Packed_field_number:
-				fd.L1.HasPacked = true
-				fd.L1.IsPacked = protowire.DecodeBool(v)
+				fd.L1.EditionFeatures.IsPacked = protowire.DecodeBool(v)
 			case genid.FieldOptions_Weak_field_number:
 				fd.L1.IsWeak = protowire.DecodeBool(v)
 			case FieldOptions_EnforceUTF8:
-				fd.L1.HasEnforceUTF8 = true
-				fd.L1.EnforceUTF8 = protowire.DecodeBool(v)
+				fd.L1.EditionFeatures.IsUTF8Validated = protowire.DecodeBool(v)
 			}
 		case protowire.BytesType:
 			v, m := protowire.ConsumeBytes(b)
@@ -548,7 +551,6 @@ func (od *Oneof) unmarshalFull(b []byte, sb *strs.Builder, pf *File, pd protoref
 func (xd *Extension) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawTypeName []byte
 	var rawOptions []byte
-	xd.L1.EditionFeatures = featuresFromParentDesc(xd.L1.Extendee)
 	xd.L2 = new(ExtensionL2)
 	for len(b) > 0 {
 		num, typ, n := protowire.ConsumeTag(b)
@@ -572,7 +574,6 @@ func (xd *Extension) unmarshalFull(b []byte, sb *strs.Builder) {
 			case genid.FieldDescriptorProto_TypeName_field_number:
 				rawTypeName = v
 			case genid.FieldDescriptorProto_Options_field_number:
-				xd.unmarshalOptions(v)
 				rawOptions = appendOptions(rawOptions, v)
 			}
 		default:
@@ -580,12 +581,6 @@ func (xd *Extension) unmarshalFull(b []byte, sb *strs.Builder) {
 			b = b[m:]
 		}
 	}
-	if xd.Syntax() == protoreflect.Editions && xd.L1.Kind == protoreflect.MessageKind && xd.L1.EditionFeatures.IsDelimitedEncoded {
-		xd.L1.Kind = protoreflect.GroupKind
-	}
-	if xd.Syntax() == protoreflect.Editions && xd.L1.EditionFeatures.IsLegacyRequired {
-		xd.L1.Cardinality = protoreflect.Required
-	}
 	if rawTypeName != nil {
 		name := makeFullName(sb, rawTypeName)
 		switch xd.L1.Kind {
@@ -598,32 +593,6 @@ func (xd *Extension) unmarshalFull(b []byte, sb *strs.Builder) {
 	xd.L2.Options = xd.L0.ParentFile.builder.optionsUnmarshaler(&descopts.Field, rawOptions)
 }
 
-func (xd *Extension) unmarshalOptions(b []byte) {
-	for len(b) > 0 {
-		num, typ, n := protowire.ConsumeTag(b)
-		b = b[n:]
-		switch typ {
-		case protowire.VarintType:
-			v, m := protowire.ConsumeVarint(b)
-			b = b[m:]
-			switch num {
-			case genid.FieldOptions_Packed_field_number:
-				xd.L2.IsPacked = protowire.DecodeBool(v)
-			}
-		case protowire.BytesType:
-			v, m := protowire.ConsumeBytes(b)
-			b = b[m:]
-			switch num {
-			case genid.FieldOptions_Features_field_number:
-				xd.L1.EditionFeatures = unmarshalFeatureSet(v, xd.L1.EditionFeatures)
-			}
-		default:
-			m := protowire.ConsumeFieldValue(num, typ, b)
-			b = b[m:]
-		}
-	}
-}
-
 func (sd *Service) unmarshalFull(b []byte, sb *strs.Builder) {
 	var rawMethods [][]byte
 	var rawOptions []byte