Core: exempt destination guardrails — first-party restriction, legal basis, audit trail

[tyssejc]

Problem

The "exempt" consent category has zero guardrails. Any destination can be marked exempt — including third-party ad networks and retargeting pixels. There's no validation, no allowlisting, and no audit trail.

Research findings (from privacy law, technical architecture, and adversarial review):

• ePrivacy Art 5(3) covers all client-initiated network requests, not just cookies (EDPB Guidelines 2/2023)
• "Exempt" is not a legal exemption — it requires an independent legal basis (GDPR Art 6(1)(f) legitimate interest)
• No industry precedent for invisible consent bypass (Segment, RudderStack, GA4 all make destinations visible)
• Privacy auditors would flag undisclosed exempt data flows as a GDPR Art 5(1)(a) transparency violation

See: agent-os/standards/core/necessary-vs-exempt.md

Proposed Changes

1. First-party restriction

Validate at config time that exempt destinations are first-party or contractually bound processors (Sentry, Datadog — not ad networks). Options:

• Allowlist of known first-party observability vendors
• firstPartyOnly: true flag + domain validation
• Console warning when exempt destinations send data

2. Legal basis declaration

Add optional legalBasis field to DestinationEntry:

{
  destination: sentry,
  config: { /* ... */ },
  consent: ["exempt"],
  legalBasis: "legitimate-interest", // or "contract-necessity", "statistical-exception"
}

Even if unenforced today, this metadata is critical for audits and future regulation.

3. Audit trail

• Include is_exempt: true in event context when dispatched to exempt destinations
• Emit destination:exempt collector events for debug panel and monitoring

4. Runtime warnings

In debug mode, log a console warning when exempt destinations receive events — makes the data flow visible during development.

Files

• packages/core/src/types.ts — DestinationEntry needs legalBasis field
• packages/core/src/collector.ts — validation in addDestination(), exempt metadata in dispatch
• packages/core/src/types.ts — CollectorEvent needs destination:exempt

Context

Identified during research into the necessary vs. exempt distinction. See standard: agent-os/standards/core/necessary-vs-exempt.md