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/contrib/instrumentation/net/http/otelhttp/labeler.go

@@ -0,0 +1,58 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otelhttp // import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+
+import (
+	"context"
+	"sync"
+
+	"go.opentelemetry.io/otel/attribute"
+)
+
+// Labeler is used to allow instrumented HTTP handlers to add custom attributes to
+// the metrics recorded by the net/http instrumentation.
+type Labeler struct {
+	mu         sync.Mutex
+	attributes []attribute.KeyValue
+}
+
+// Add attributes to a Labeler.
+func (l *Labeler) Add(ls ...attribute.KeyValue) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	l.attributes = append(l.attributes, ls...)
+}
+
+// Get returns a copy of the attributes added to the Labeler.
+func (l *Labeler) Get() []attribute.KeyValue {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	ret := make([]attribute.KeyValue, len(l.attributes))
+	copy(ret, l.attributes)
+	return ret
+}
+
+type labelerContextKeyType int
+
+const labelerContextKey labelerContextKeyType = 0
+
+// ContextWithLabeler returns a new context with the provided Labeler instance.
+// Attributes added to the specified labeler will be injected into metrics
+// emitted by the instrumentation. Only one labeller can be injected into the
+// context. Injecting it multiple times will override the previous calls.
+func ContextWithLabeler(parent context.Context, l *Labeler) context.Context {
+	return context.WithValue(parent, labelerContextKey, l)
+}
+
+// LabelerFromContext retrieves a Labeler instance from the provided context if
+// one is available.  If no Labeler was found in the provided context a new, empty
+// Labeler is returned and the second return value is false.  In this case it is
+// safe to use the Labeler but any attributes added to it will not be used.
+func LabelerFromContext(ctx context.Context) (*Labeler, bool) {
+	l, ok := ctx.Value(labelerContextKey).(*Labeler)
+	if !ok {
+		l = &Labeler{}
+	}
+	return l, ok
+}