Add control cost / benefit fields to support treatment decisions

[JohnASRG]

Motivation

controls[] and riskTreatmentDecisions[] currently support implementation status and justification text, but no structured economic context. Real treatment decisions weigh implementation cost, lifecycle cost, and treatment benefit — all important inputs to risk acceptance discussions. Adding optional structured fields makes those tradeoffs portable across tools.

Proposed change

On controls[]:

• implementationEstimate: { amount, currency, basis: "engineering-hours"|"capex"|"opex"|"composite" }
• lifecycleCost: same shape, period: "annual"|"total-of-ownership"
• implementationOwnerPartyRef (uses parties[] from Add distributed cybersecurity activities and supplier responsibility model #58)

On riskTreatmentDecisions[]:

• treatmentBenefitRationale
• expectedRiskReduction: { from: bandBefore, to: bandAfter, confidence }
• decisionCostRationale

All fields optional; existing examples continue to validate without modification.

References

• AI peer review, "Open topic — Controls cost" and "Recommended backlog"

Acceptance criteria

• Schema fields added (JSON + XSD)
• Example demonstrates a control with implementation estimate and a treatment decision with expected risk reduction
• Methodology note explains that monetary values are advisory only

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Surfaced by external AI peer review; see chat transcript for full review text.