- ApplyBranches and ApplyGates now clone steps before modifying,
matching the immutability pattern of ApplyLoops and ApplyAdvice
- Added internal applyBranchesWithMap/applyGatesWithMap for efficiency
- ApplyControlFlow builds stepMap once for both (gt-gpgdv optimization)
- Added cloneStepsRecursive helper
- Added TestApplyBranches_Immutability and TestApplyGates_Immutability
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>