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/client.go

@@ -0,0 +1,50 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otelhttp // import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+// DefaultClient is the default Client and is used by Get, Head, Post and PostForm.
+// Please be careful of initialization order - for example, if you change
+// the global propagator, the DefaultClient might still be using the old one.
+var DefaultClient = &http.Client{Transport: NewTransport(http.DefaultTransport)}
+
+// Get is a convenient replacement for http.Get that adds a span around the request.
+func Get(ctx context.Context, targetURL string) (resp *http.Response, err error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, targetURL, http.NoBody)
+	if err != nil {
+		return nil, err
+	}
+	return DefaultClient.Do(req)
+}
+
+// Head is a convenient replacement for http.Head that adds a span around the request.
+func Head(ctx context.Context, targetURL string) (resp *http.Response, err error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodHead, targetURL, http.NoBody)
+	if err != nil {
+		return nil, err
+	}
+	return DefaultClient.Do(req)
+}
+
+// Post is a convenient replacement for http.Post that adds a span around the request.
+func Post(ctx context.Context, targetURL, contentType string, body io.Reader) (resp *http.Response, err error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, targetURL, body)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", contentType)
+	return DefaultClient.Do(req)
+}
+
+// PostForm is a convenient replacement for http.PostForm that adds a span around the request.
+func PostForm(ctx context.Context, targetURL string, data url.Values) (resp *http.Response, err error) {
+	return Post(ctx, targetURL, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
+}