Load-test the record store at the target page-load rate with provider refreshes #1576

Summary

Load-test the record store at the target page-load rate with provider refreshes.

Part of #1558, server-side identity on every adapter. Plan ID A5, planned in wave 9 (MVP: Fastly and Axum); priority P1, size M. Design: spec; order and dependencies: plan.

Requirements

AX-4 Record store fit for production

Writes are spread across partition keys by listing prefix: an EC row's partition is its IP hash, and a withdrawal marker's is the marker prefix and its EC ID, so no item is updated by every insert and listing stays strong within a partition (EZI-2a). Retries are bounded.

Current state

What the code does today, from the design's survey at the revisions it names:

• AX-4: Extract native EC lifecycle and DynamoDB persistence #1536 puts every row under one partition key and updates one allocator item per insert, and Add native AWS store providers edgezero#414's DynamoDB store keeps every key in one partition.

Acceptance criteria

• AX-4: A load test at the target page-load rate with provider refreshes (A5 sets the rate) shows no throttling, and rows from different IP hashes land in different partitions

Dependencies

Blocked by:

• Identity on Axum through T21's shared app #1574 Identity on Axum through T21's shared app (new in this plan)
• Axum reference infrastructure #1578 Axum reference infrastructure (new in this plan)
• Identity features pass on Axum from the shared app #1581 Identity features pass on Axum from the shared app (new in this plan)