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Delfour Insight Economy
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See https://ruben.verborgh.org/blog/2025/08/12/inside-the-insight-economy/

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Delfour — PHONE side
Inputs:
  - profile graph (may contain sensitive facts)
  - session context (retailer/device/event + created/expiry timestamps)
Outputs (pass-only-new):
  - a neutral ins:Insight (no sensitive terms)
  - an ODRL policy envelope derived from the insight
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Delfour — SCANNER side
Inputs:
  - an ins:Insight (neutral envelope)
  - the ODRL policy (derived from the insight)
  - a request to use the insight with purpose=shopping_assist
  - "now" as xsd:dateTime (for expiry guard)
  - a small product catalog + a scan event (scanned product)
Outputs (pass-only-new):
  - authorization marking (Allowed / Blocked with reason)
  - derived expiry flag (ex:Expired) when past expiresAt
  - an audit trail (act:Decision, optionally a delete_due Duty)
  - a runtime suggestion banner (shop:suggestedAlternative)
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