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/metric/doc.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 metric provides the OpenTelemetry API used to measure metrics about
@@ -68,6 +57,23 @@ asynchronous measurement, a Gauge ([Int64ObservableGauge] and
 See the [OpenTelemetry documentation] for more information about instruments
 and their intended use.
 
+# Instrument Name
+
+OpenTelemetry defines an [instrument name syntax] that restricts what
+instrument names are allowed.
+
+Instrument names should ...
+
+  - Not be empty.
+  - Have an alphabetic character as their first letter.
+  - Have any letter after the first be an alphanumeric character, ‘_’, ‘.’,
+    ‘-’, or ‘/’.
+  - Have a maximum length of 255 letters.
+
+To ensure compatibility with observability platforms, all instruments created
+need to conform to this syntax. Not all implementations of the API will validate
+these names, it is the callers responsibility to ensure compliance.
+
 # Measurements
 
 Measurements are made by recording values and information about the values with
@@ -149,7 +155,7 @@ of [go.opentelemetry.io/otel/metric].
 
 Finally, an author can embed another implementation in theirs. The embedded
 implementation will be used for methods not defined by the author. For example,
-an author who want to default to silently dropping the call can use
+an author who wants to default to silently dropping the call can use
 [go.opentelemetry.io/otel/metric/noop]:
 
 	import "go.opentelemetry.io/otel/metric/noop"
@@ -164,6 +170,7 @@ It is strongly recommended that authors only embed
 That implementation is the only one OpenTelemetry authors can guarantee will
 fully implement all the API interfaces when a user updates their API.
 
+[instrument name syntax]: https://opentelemetry.io/docs/specs/otel/metrics/api/#instrument-name-syntax
 [OpenTelemetry documentation]: https://opentelemetry.io/docs/concepts/signals/metrics/
 [GetMeterProvider]: https://pkg.go.dev/go.opentelemetry.io/otel#GetMeterProvider
 */