plan validate Command

Summary

Structural validation for plan files with CI-friendly exit codes. Checks for broken references, duplicate IDs, invalid attribute values, circular dependencies, and consistency issues. Add npx refrakt plan validate --strict to CI in one line.

Acceptance Criteria

• Detects broken ref/xref links — entity ID not found (error)
• Detects duplicate IDs across all plan files (error)
• Detects invalid status, priority, and severity values (error)
• Detects circular dependencies (error)
• Detects orphaned work items with no milestone assigned (warning)
• Detects completed milestones with open work items (warning)
• --strict promotes warnings to errors
• Exit codes: 0 = clean, 1 = errors found, 2 = bad arguments
• --format json for programmatic consumption
• Tests for each check type

Dependencies

• CLI Plugin Discovery Architecture (plugin architecture)
• Plan File Scanner Library (plan file scanner)

References

• Plan CLI (Plan CLI)