concurrency policy

[pelikhan]

You are working on implementing a concurrency policy computation system for the GitHub Agentic Workflows (gh-aw) tool. This Go-based GitHub CLI extension converts markdown workflow files into GitHub Actions YAML, and you need to add intelligent concurrency management.

CONTEXT: Issue #820 requests a sophisticated concurrency policy system that computes default policies from multiple sources and allows user overrides. The system should merge policies from different contexts (workflow, issue-specific, PR-specific) into a final concurrency configuration.

CORE REQUIREMENTS:

1. Implement a policy merging system that combines multiple policy sources
2. Support default policies: workflow (default), issue.number with cancel, pull_request with cancel, and alias policies
3. Merge all policy keys and concatenate values to generate final concurrency policy
4. Allow user-provided values to override computed policies
5. Generate proper GitHub Actions concurrency YAML from the computed policies

TECHNICAL IMPLEMENTATION:

• Extend the workflow compiler in pkg/workflow/compiler.go to handle concurrency policy computation
• Modify the frontmatter parser in pkg/parser/ to parse concurrency policy configurations
• Implement JSON schema processing for policy definitions with structure like: {"*": {"id": "workflow"}, "issues": {"node": "issue.number"}, "pull_requests": {"node": "pull_requests.number"}}
• Add YAML generation logic to output valid GitHub Actions concurrency sections
• Ensure backward compatibility with existing workflows

KEY CONSTRAINTS:

• Follow existing Go code patterns and console message formatting using pkg/console/console.go
• Use the Makefile build system and ensure all changes pass make agent-finish validation
• Add comprehensive unit tests for policy merging scenarios
• Support different workflow trigger types (issues, pull_requests, schedule, manual)
• Validate policy configurations and provide helpful error messages
• Maintain performance during workflow compilation

TESTING REQUIREMENTS:

• Test basic policy merging with default plus context-specific policies
• Verify user override behavior takes precedence over computed policies
• Test different GitHub Actions trigger types and their appropriate concurrency rules
• Handle edge cases like empty policies, conflicting keys, invalid configurations
• Validate generated YAML syntax is correct for GitHub Actions

CODEBASE CONTEXT:

• This is a Go project using cobra CLI framework
• Main entry point is cmd/gh-aw/main.go
• Core packages are in pkg/cli/, pkg/parser/, pkg/workflow/
• Use existing patterns from similar compiler enhancements
• Follow the project's console formatting conventions for user-facing output
• Ensure generated .lock.yml files contain proper concurrency sections

Focus on implementing the policy computation logic that merges multiple policy sources into a final concurrency configuration, while maintaining the existing workflow compilation architecture and providing clear error handling and validation.