Fix main coverage failure in core/framework

[davidahmann]

Summary

• fix main workflow failure from run 22148557483
• raise core/framework package coverage back above the 85% gate
• add targeted validation tests for framework parsing and control validation branches

Validation

• go test ./core/framework -coverprofile=/tmp/framework.cov
• go tool cover -func=/tmp/framework.cov (core/framework now 93.0%)
• go test ./... -coverprofile=coverage.out
• ./scripts/check_go_package_coverage.py coverage.out 85 github.com/Clyra-AI/proof/core/exitcode,github.com/Clyra-AI/proof/internal/testutil