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/go.opentelemetry.io/otel/internal/global/handler.go

@@ -1,37 +1,12 @@
 // Copyright The OpenTelemetry Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+// SPDX-License-Identifier: Apache-2.0
 
+// Package global provides the OpenTelemetry global API.
 package global // import "go.opentelemetry.io/otel/internal/global"
 
 import (
 	"log"
-	"os"
 	"sync/atomic"
-	"unsafe"
-)
-
-var (
-	// GlobalErrorHandler provides an ErrorHandler that can be used
-	// throughout an OpenTelemetry instrumented project. When a user
-	// specified ErrorHandler is registered (`SetErrorHandler`) all calls to
-	// `Handle` and will be delegated to the registered ErrorHandler.
-	GlobalErrorHandler = defaultErrorHandler()
-
-	// Compile-time check that delegator implements ErrorHandler.
-	_ ErrorHandler = (*ErrDelegator)(nil)
-	// Compile-time check that errLogger implements ErrorHandler.
-	_ ErrorHandler = (*ErrLogger)(nil)
 )
 
 // ErrorHandler handles irremediable events.
@@ -42,62 +17,21 @@ type ErrorHandler interface {
 }
 
 type ErrDelegator struct {
-	delegate unsafe.Pointer
+	delegate atomic.Pointer[ErrorHandler]
 }
 
+// Compile-time check that delegator implements ErrorHandler.
+var _ ErrorHandler = (*ErrDelegator)(nil)
+
 func (d *ErrDelegator) Handle(err error) {
-	d.getDelegate().Handle(err)
-}
-
-func (d *ErrDelegator) getDelegate() ErrorHandler {
-	return *(*ErrorHandler)(atomic.LoadPointer(&d.delegate))
+	if eh := d.delegate.Load(); eh != nil {
+		(*eh).Handle(err)
+		return
+	}
+	log.Print(err)
 }
 
 // setDelegate sets the ErrorHandler delegate.
 func (d *ErrDelegator) setDelegate(eh ErrorHandler) {
-	atomic.StorePointer(&d.delegate, unsafe.Pointer(&eh))
-}
-
-func defaultErrorHandler() *ErrDelegator {
-	d := &ErrDelegator{}
-	d.setDelegate(&ErrLogger{l: log.New(os.Stderr, "", log.LstdFlags)})
-	return d
-}
-
-// ErrLogger logs errors if no delegate is set, otherwise they are delegated.
-type ErrLogger struct {
-	l *log.Logger
-}
-
-// Handle logs err if no delegate is set, otherwise it is delegated.
-func (h *ErrLogger) Handle(err error) {
-	h.l.Print(err)
-}
-
-// GetErrorHandler returns the global ErrorHandler instance.
-//
-// The default ErrorHandler instance returned will log all errors to STDERR
-// until an override ErrorHandler is set with SetErrorHandler. All
-// ErrorHandler returned prior to this will automatically forward errors to
-// the set instance instead of logging.
-//
-// Subsequent calls to SetErrorHandler after the first will not forward errors
-// to the new ErrorHandler for prior returned instances.
-func GetErrorHandler() ErrorHandler {
-	return GlobalErrorHandler
-}
-
-// SetErrorHandler sets the global ErrorHandler to h.
-//
-// The first time this is called all ErrorHandler previously returned from
-// GetErrorHandler will send errors to h instead of the default logging
-// ErrorHandler. Subsequent calls will set the global ErrorHandler, but not
-// delegate errors to h.
-func SetErrorHandler(h ErrorHandler) {
-	GlobalErrorHandler.setDelegate(h)
-}
-
-// Handle is a convenience function for ErrorHandler().Handle(err).
-func Handle(err error) {
-	GetErrorHandler().Handle(err)
+	d.delegate.Store(&eh)
 }