Fix contact subscription and verification semantics for list/campaign sends

[alexeygrigorev]

Context

CMP will rely on Datamailer contacts for campaigns and future recipient-list sends. The current contact state semantics are not safe enough for this.

Observed during CMP/Datamailer protocol review:

• CMP contact upsert examples use status: subscribed, but existing CMP sync may omit it during some flows.
• Datamailer defaults missing contact upsert status to pending.
• Campaign snapshot logic skips contacts whose client/audience subscription is not subscribed.
• verified=true in the contact API verifies the subscription, but campaign snapshot eligibility checks the global contact verification timestamp.
• Contact status and campaign snapshot should agree about whether a contact can receive marketing/list/campaign email.

Desired behavior

• Contact upsert with status=subscribed and verified=true makes the contact eligible for marketing/list/campaign sends unless suppressed.
• Contact status and campaign/list snapshot eligibility use the same verification/subscription semantics.
• Transactional sends continue to bypass marketing unsubscribe where appropriate, but still respect hard suppressions such as hard bounce and complaint.

Acceptance criteria

• Add or update tests showing a contact upserted through the client API with status=subscribed and verified=true is eligible for campaign/list snapshot.
• Contact status can_send_marketing matches campaign/list eligibility for the same contact.
• Pending/unsubscribed contacts are skipped from campaign/list sends.
• Hard bounced or complained contacts are skipped/suppressed.
• Document the exact meaning of verified=true for contacts and subscriptions.

Related

This blocks Datamailer recipient lists and CMP-driven course email targeting.

[alexeygrigorev]

Implemented and deployed to sandbox. Contact upsert and eligibility semantics now align: status=subscribed plus verified=true makes contacts eligible for campaign/list sends unless unsubscribed or hard-suppressed, and docs/tests cover the behavior.