test: route-level coverage for verdict_source owner-scope gate

[bokelley]

Gap

PR #4263 added `verdict_source` as an owner-scoped field on `/api/registry/agents/:url/compliance`. Gated on `ownerMembership.is_owner`: populated for the agent's owner, null for everyone else (anonymous, cross-org, non-member).

No route-level test currently asserts this gate. The unit test in `server/tests/unit/membership-tiers.test.ts` covers `resolveOwnerMembership` returning the right shape, but doesn't pin the route-level wiring that gates the field on `is_owner`.

If a future refactor flips the gate (e.g. accidentally exposes `verdict_source` to anonymous callers), nothing catches it.

Fix shape

Add to `server/tests/integration/registry-api.test.ts` (or appropriate compliance-route test file) three assertions:

1. Anonymous caller hitting `/api/registry/agents/:url/compliance` for a passing agent → response includes `verdict_source: null`
2. Authenticated cross-org caller → `verdict_source: null`
3. Authenticated owner → `verdict_source` populated with the actual `triggered_by` value (`'heartbeat'` / `'owner_test'` / `'manual'` / `'webhook'`)

Bonus: assert response `Object.keys()` is identical between owner and non-owner cases (owner-detection-resistance invariant).

Acceptance criteria

• Three integration tests covering the cases above
• All pass against current main
• A purposeful regression (e.g. dropping the `is_owner` gate) makes them fail

Discovered

PR #4263 code review feedback. Deferred as out-of-scope.

[bokelley]

Partial completion via #4389 (merged 2026-05-11).

Shipped 6 explicit unit tests pinning the is_owner semantics in resolveOwnerMembership — the load-bearing gate for verdict_source on the public compliance API. Anonymous, non-owner, orphan profile, free Explorer tier (still is_owner=true), API-access tier, canceled sub. Anchors the invariant that is_owner is broader than is_api_access_tier.

Still deferred (this issue stays open): the original ask was for a route-level integration test — request(app).get('/api/registry/agents/:url/compliance').expect(...) against three caller shapes (anonymous, cross-org, owner). That needs DB-fixture scaffolding not currently in place for the compliance endpoint. Adding the scaffolding is a bigger refactor; the unit-test coverage above is the next-best safety net in the meantime.