V5: Composition -> SMS drift check via Pet Data

[ckrough]

Complexity: M · Blocked on external: SMS API access (via Pet Data)

Scope

Implement the Composition -> SMS hop as a ChannelAdapter-shaped read that pulls the animal's current SMS-sourced card through Pet Data's extraction (no second SMS connector in this service) and returns a ListingSnapshot for diffing.

Where the shelter's SMS exposes an API, that access lands in Pet Data's config; the listings service consumes Pet Data's extracted current card. This is the drift-prone manual-entry hop, so it is the highest-value check in the epic.

Out of scope

• The diff/compliance computation (V6: Diff / compliance engine #308).

Dependencies

• Blocked by: V2: Compliance data model + source-of-truth resolution + Alembic + org RLS #304 (snapshot shape + resolver).
• External: SMS API access provisioned in Pet Data (this ticket stays blocked until available).
• Blocks: V6: Diff / compliance engine #308.

Acceptance criteria

• The SMS hop returns a ListingSnapshot built from Pet Data's current extracted card for a fixture animal (asserted; the Pet Data client is mocked).
• No module under src/listings/ opens its own SMS connection or imports an SMS SDK (grep-asserted); the SMS read goes through the Pet Data client only.
• Absent SMS data maps to a "not entered" snapshot rather than an exception (test).

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ADR: docs/adr/0033-listing-sync-verification.md. Epic: #302.
Tenant-data path: high-risk, blocked.