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/state.go

@@ -1,16 +1,5 @@
 // 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 // import "go.opentelemetry.io/otel/internal/global"
 
@@ -25,6 +14,10 @@ import (
 )
 
 type (
+	errorHandlerHolder struct {
+		eh ErrorHandler
+	}
+
 	tracerProviderHolder struct {
 		tp trace.TracerProvider
 	}
@@ -39,15 +32,59 @@ type (
 )
 
 var (
+	globalErrorHandler  = defaultErrorHandler()
 	globalTracer        = defaultTracerValue()
 	globalPropagators   = defaultPropagatorsValue()
 	globalMeterProvider = defaultMeterProvider()
 
+	delegateErrorHandlerOnce      sync.Once
 	delegateTraceOnce             sync.Once
 	delegateTextMapPropagatorOnce sync.Once
 	delegateMeterOnce             sync.Once
 )
 
+// 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.Load().(errorHandlerHolder).eh
+}
+
+// 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) {
+	current := GetErrorHandler()
+
+	if _, cOk := current.(*ErrDelegator); cOk {
+		if _, ehOk := h.(*ErrDelegator); ehOk && current == h {
+			// Do not assign to the delegate of the default ErrDelegator to be
+			// itself.
+			Error(
+				errors.New("no ErrorHandler delegate configured"),
+				"ErrorHandler remains its current value.",
+			)
+			return
+		}
+	}
+
+	delegateErrorHandlerOnce.Do(func() {
+		if def, ok := current.(*ErrDelegator); ok {
+			def.setDelegate(h)
+		}
+	})
+	globalErrorHandler.Store(errorHandlerHolder{eh: h})
+}
+
 // TracerProvider is the internal implementation for global.TracerProvider.
 func TracerProvider() trace.TracerProvider {
 	return globalTracer.Load().(tracerProviderHolder).tp
@@ -63,7 +100,7 @@ func SetTracerProvider(tp trace.TracerProvider) {
 			// to itself.
 			Error(
 				errors.New("no delegate configured in tracer provider"),
-				"Setting tracer provider to it's current value. No delegate will be configured",
+				"Setting tracer provider to its current value. No delegate will be configured",
 			)
 			return
 		}
@@ -92,7 +129,7 @@ func SetTextMapPropagator(p propagation.TextMapPropagator) {
 			// delegate to itself.
 			Error(
 				errors.New("no delegate configured in text map propagator"),
-				"Setting text map propagator to it's current value. No delegate will be configured",
+				"Setting text map propagator to its current value. No delegate will be configured",
 			)
 			return
 		}
@@ -123,7 +160,7 @@ func SetMeterProvider(mp metric.MeterProvider) {
 			// to itself.
 			Error(
 				errors.New("no delegate configured in meter provider"),
-				"Setting meter provider to it's current value. No delegate will be configured",
+				"Setting meter provider to its current value. No delegate will be configured",
 			)
 			return
 		}
@@ -137,6 +174,12 @@ func SetMeterProvider(mp metric.MeterProvider) {
 	globalMeterProvider.Store(meterProviderHolder{mp: mp})
 }
 
+func defaultErrorHandler() *atomic.Value {
+	v := &atomic.Value{}
+	v.Store(errorHandlerHolder{eh: &ErrDelegator{}})
+	return v
+}
+
 func defaultTracerValue() *atomic.Value {
 	v := &atomic.Value{}
 	v.Store(tracerProviderHolder{tp: &tracerProvider{}})