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/instrument.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 // import "go.opentelemetry.io/otel/metric"
 
@@ -27,6 +16,7 @@ type InstrumentOption interface {
 	Int64CounterOption
 	Int64UpDownCounterOption
 	Int64HistogramOption
+	Int64GaugeOption
 	Int64ObservableCounterOption
 	Int64ObservableUpDownCounterOption
 	Int64ObservableGaugeOption
@@ -34,11 +24,18 @@ type InstrumentOption interface {
 	Float64CounterOption
 	Float64UpDownCounterOption
 	Float64HistogramOption
+	Float64GaugeOption
 	Float64ObservableCounterOption
 	Float64ObservableUpDownCounterOption
 	Float64ObservableGaugeOption
 }
 
+// HistogramOption applies options to histogram instruments.
+type HistogramOption interface {
+	Int64HistogramOption
+	Float64HistogramOption
+}
+
 type descOpt string
 
 func (o descOpt) applyFloat64Counter(c Float64CounterConfig) Float64CounterConfig {
@@ -56,12 +53,19 @@ func (o descOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64Histogra
 	return c
 }
 
+func (o descOpt) applyFloat64Gauge(c Float64GaugeConfig) Float64GaugeConfig {
+	c.description = string(o)
+	return c
+}
+
 func (o descOpt) applyFloat64ObservableCounter(c Float64ObservableCounterConfig) Float64ObservableCounterConfig {
 	c.description = string(o)
 	return c
 }
 
-func (o descOpt) applyFloat64ObservableUpDownCounter(c Float64ObservableUpDownCounterConfig) Float64ObservableUpDownCounterConfig {
+func (o descOpt) applyFloat64ObservableUpDownCounter(
+	c Float64ObservableUpDownCounterConfig,
+) Float64ObservableUpDownCounterConfig {
 	c.description = string(o)
 	return c
 }
@@ -86,12 +90,19 @@ func (o descOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfi
 	return c
 }
 
+func (o descOpt) applyInt64Gauge(c Int64GaugeConfig) Int64GaugeConfig {
+	c.description = string(o)
+	return c
+}
+
 func (o descOpt) applyInt64ObservableCounter(c Int64ObservableCounterConfig) Int64ObservableCounterConfig {
 	c.description = string(o)
 	return c
 }
 
-func (o descOpt) applyInt64ObservableUpDownCounter(c Int64ObservableUpDownCounterConfig) Int64ObservableUpDownCounterConfig {
+func (o descOpt) applyInt64ObservableUpDownCounter(
+	c Int64ObservableUpDownCounterConfig,
+) Int64ObservableUpDownCounterConfig {
 	c.description = string(o)
 	return c
 }
@@ -121,12 +132,19 @@ func (o unitOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64Histogra
 	return c
 }
 
+func (o unitOpt) applyFloat64Gauge(c Float64GaugeConfig) Float64GaugeConfig {
+	c.unit = string(o)
+	return c
+}
+
 func (o unitOpt) applyFloat64ObservableCounter(c Float64ObservableCounterConfig) Float64ObservableCounterConfig {
 	c.unit = string(o)
 	return c
 }
 
-func (o unitOpt) applyFloat64ObservableUpDownCounter(c Float64ObservableUpDownCounterConfig) Float64ObservableUpDownCounterConfig {
+func (o unitOpt) applyFloat64ObservableUpDownCounter(
+	c Float64ObservableUpDownCounterConfig,
+) Float64ObservableUpDownCounterConfig {
 	c.unit = string(o)
 	return c
 }
@@ -151,12 +169,19 @@ func (o unitOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfi
 	return c
 }
 
+func (o unitOpt) applyInt64Gauge(c Int64GaugeConfig) Int64GaugeConfig {
+	c.unit = string(o)
+	return c
+}
+
 func (o unitOpt) applyInt64ObservableCounter(c Int64ObservableCounterConfig) Int64ObservableCounterConfig {
 	c.unit = string(o)
 	return c
 }
 
-func (o unitOpt) applyInt64ObservableUpDownCounter(c Int64ObservableUpDownCounterConfig) Int64ObservableUpDownCounterConfig {
+func (o unitOpt) applyInt64ObservableUpDownCounter(
+	c Int64ObservableUpDownCounterConfig,
+) Int64ObservableUpDownCounterConfig {
 	c.unit = string(o)
 	return c
 }
@@ -167,8 +192,27 @@ func (o unitOpt) applyInt64ObservableGauge(c Int64ObservableGaugeConfig) Int64Ob
 }
 
 // WithUnit sets the instrument unit.
+//
+// The unit u should be defined using the appropriate [UCUM](https://ucum.org) case-sensitive code.
 func WithUnit(u string) InstrumentOption { return unitOpt(u) }
 
+// WithExplicitBucketBoundaries sets the instrument explicit bucket boundaries.
+//
+// This option is considered "advisory", and may be ignored by API implementations.
+func WithExplicitBucketBoundaries(bounds ...float64) HistogramOption { return bucketOpt(bounds) }
+
+type bucketOpt []float64
+
+func (o bucketOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
+func (o bucketOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
 // AddOption applies options to an addition measurement. See
 // [MeasurementOption] for other options that can be used as an AddOption.
 type AddOption interface {
@@ -315,7 +359,7 @@ func WithAttributeSet(attributes attribute.Set) MeasurementOption {
 //
 //	cp := make([]attribute.KeyValue, len(attributes))
 //	copy(cp, attributes)
-//	WithAttributes(attribute.NewSet(cp...))
+//	WithAttributeSet(attribute.NewSet(cp...))
 //
 // [attribute.NewSet] may modify the passed attributes so this will make a copy
 // of attributes before creating a set in order to ensure this function is