Add loop, branch, and gate operators for formula step transformation:
- LoopSpec: Fixed-count loops expand body N times with chained iterations.
Conditional loops expand once with runtime metadata labels.
- BranchRule: Fork-join patterns wire dependencies for parallel paths.
- GateRule: Adds condition labels for runtime evaluation before steps.
Types added to types.go:
- LoopSpec (count/until/max/body)
- BranchRule (from/steps/join)
- GateRule (before/condition)
- Loop field on Step
- Branch/Gate arrays on ComposeRules
New controlflow.go with ApplyLoops, ApplyBranches, ApplyGates, and
ApplyControlFlow convenience function. Wired into cook.go before
advice and expansion operators.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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