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/github.com/opencontainers/image-spec/specs-go/v1/annotations.go

@@ -0,0 +1,62 @@
+// Copyright 2016 The Linux Foundation
+//
+// 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.
+
+package v1
+
+const (
+	// AnnotationCreated is the annotation key for the date and time on which the image was built (date-time string as defined by RFC 3339).
+	AnnotationCreated = "org.opencontainers.image.created"
+
+	// AnnotationAuthors is the annotation key for the contact details of the people or organization responsible for the image (freeform string).
+	AnnotationAuthors = "org.opencontainers.image.authors"
+
+	// AnnotationURL is the annotation key for the URL to find more information on the image.
+	AnnotationURL = "org.opencontainers.image.url"
+
+	// AnnotationDocumentation is the annotation key for the URL to get documentation on the image.
+	AnnotationDocumentation = "org.opencontainers.image.documentation"
+
+	// AnnotationSource is the annotation key for the URL to get source code for building the image.
+	AnnotationSource = "org.opencontainers.image.source"
+
+	// AnnotationVersion is the annotation key for the version of the packaged software.
+	// The version MAY match a label or tag in the source code repository.
+	// The version MAY be Semantic versioning-compatible.
+	AnnotationVersion = "org.opencontainers.image.version"
+
+	// AnnotationRevision is the annotation key for the source control revision identifier for the packaged software.
+	AnnotationRevision = "org.opencontainers.image.revision"
+
+	// AnnotationVendor is the annotation key for the name of the distributing entity, organization or individual.
+	AnnotationVendor = "org.opencontainers.image.vendor"
+
+	// AnnotationLicenses is the annotation key for the license(s) under which contained software is distributed as an SPDX License Expression.
+	AnnotationLicenses = "org.opencontainers.image.licenses"
+
+	// AnnotationRefName is the annotation key for the name of the reference for a target.
+	// SHOULD only be considered valid when on descriptors on `index.json` within image layout.
+	AnnotationRefName = "org.opencontainers.image.ref.name"
+
+	// AnnotationTitle is the annotation key for the human-readable title of the image.
+	AnnotationTitle = "org.opencontainers.image.title"
+
+	// AnnotationDescription is the annotation key for the human-readable description of the software packaged in the image.
+	AnnotationDescription = "org.opencontainers.image.description"
+
+	// AnnotationBaseImageDigest is the annotation key for the digest of the image's base image.
+	AnnotationBaseImageDigest = "org.opencontainers.image.base.digest"
+
+	// AnnotationBaseImageName is the annotation key for the image reference of the image's base image.
+	AnnotationBaseImageName = "org.opencontainers.image.base.name"
+)