Answer identify and batch sync locally on every adapter #1582

Summary

Answer identify and batch sync locally on every adapter: run them with a record store, 501 without one.

Part of #1558, server-side identity on every adapter. Plan ID T1, planned in wave 0 (MVP: Fastly and Axum); priority P0, size S. Design: spec; order and dependencies: plan.

Requirements

ID-3 Partner APIs answered locally

Identify, batch sync, pull sync and admin lookup run on every adapter with a record store. Without one, identify and batch sync return a local error and never reach the publisher origin. Admin lookup already answers 501 locally; pull sync is outbound only.

Acceptance criteria

• ID-3: In each adapter's tests a capturing origin receives no identify or batch-sync request
• ID-3: With a store they run, without one they return 501

Dependencies

Blocked by: nothing.

Blocks:

• Identity on Cloudflare through T21's shared app with EZI-2c's store, passing T5's suite #1588 Identity on Cloudflare through T21's shared app with EZI-2c's store, passing T5's suite (new in this plan)
• One identity app in core for every adapter #1600 One identity app in core for every adapter (new in this plan)