PSD.4:4.5 - Use exact scope membership only when needed

When a downstream claim depends on whether one exact U.ContextSlice belongs to one declared U.Scope, use A.2.6. Distinguish an evaluation result of true, false, or unknown. Unknown means the available basis cannot decide; obtain the missing input, narrow the attempted use, or abstain instead of asserting exclusion. Changing the extension creates a new scope; a refit that preserves the extension does not.

Do not force every ordinary concern or participant into U.Scope. PSD.4 governs the field-specific judgement that a problem boundary is usable for the current inquiry; A.2.6 governs exact contextual membership. A C.2.3 formality threshold concerns how strictly a claim is expressed and is selected separately, only when the receiving use needs it.