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/encoding/prototext/decode.go

@@ -84,7 +84,7 @@ type decoder struct {
 }
 
 // newError returns an error object with position info.
-func (d decoder) newError(pos int, f string, x ...interface{}) error {
+func (d decoder) newError(pos int, f string, x ...any) error {
 	line, column := d.Position(pos)
 	head := fmt.Sprintf("(line %d:%d): ", line, column)
 	return errors.New(head+f, x...)
@@ -96,7 +96,7 @@ func (d decoder) unexpectedTokenError(tok text.Token) error {
 }
 
 // syntaxError returns a syntax error for given position.
-func (d decoder) syntaxError(pos int, f string, x ...interface{}) error {
+func (d decoder) syntaxError(pos int, f string, x ...any) error {
 	line, column := d.Position(pos)
 	head := fmt.Sprintf("syntax error (line %d:%d): ", line, column)
 	return errors.New(head+f, x...)

vendor/google.golang.org/protobuf/encoding/prototext/encode.go

@@ -27,15 +27,17 @@ const defaultIndent = "  "
 
 // Format formats the message as a multiline string.
 // This function is only intended for human consumption and ignores errors.
-// Do not depend on the output being stable. It may change over time across
-// different versions of the program.
+// Do not depend on the output being stable. Its output will change across
+// different builds of your program, even when using the same version of the
+// protobuf module.
 func Format(m proto.Message) string {
 	return MarshalOptions{Multiline: true}.Format(m)
 }
 
 // Marshal writes the given [proto.Message] in textproto format using default
-// options. Do not depend on the output being stable. It may change over time
-// across different versions of the program.
+// options. Do not depend on the output being stable. Its output will change
+// across different builds of your program, even when using the same version of
+// the protobuf module.
 func Marshal(m proto.Message) ([]byte, error) {
 	return MarshalOptions{}.Marshal(m)
 }
@@ -84,8 +86,9 @@ type MarshalOptions struct {
 
 // Format formats the message as a string.
 // This method is only intended for human consumption and ignores errors.
-// Do not depend on the output being stable. It may change over time across
-// different versions of the program.
+// Do not depend on the output being stable. Its output will change across
+// different builds of your program, even when using the same version of the
+// protobuf module.
 func (o MarshalOptions) Format(m proto.Message) string {
 	if m == nil || !m.ProtoReflect().IsValid() {
 		return "<nil>" // invalid syntax, but okay since this is for debugging
@@ -98,8 +101,9 @@ func (o MarshalOptions) Format(m proto.Message) string {
 }
 
 // Marshal writes the given [proto.Message] in textproto format using options in
-// MarshalOptions object. Do not depend on the output being stable. It may
-// change over time across different versions of the program.
+// MarshalOptions object. Do not depend on the output being stable. Its output
+// will change across different builds of your program, even when using the
+// same version of the protobuf module.
 func (o MarshalOptions) Marshal(m proto.Message) ([]byte, error) {
 	return o.marshal(nil, m)
 }