Implement internal/formula package for parsing and validating formula.toml files:
- types.go: Formula, Step, Leg, Aspect, Template, Input, Var structs
- parser.go: TOML parsing using BurntSushi/toml, validation, dependency resolution
- Supports convoy, workflow, expansion, and aspect formula types
- Infers type from content when not explicitly set
- Validates required fields, unique IDs, and dependency references
- Detects circular dependencies in workflow steps
- Provides TopologicalSort and ReadySteps for execution planning
(gt-5chbk)
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>