Replace customer_name in the Accounts API response

Problem

Accounts API returns the customer on GET /accounts/{id} as one string, customer_name. Support and billing now need the customer's id, display name and legal name separately, and some services split the string themselves to get them. The response should carry a customer object instead.

Decision

Return the customer as a customer object (id, displayName, legalName) and stop returning customer_name, without breaking any service that reads it. Accounts API returns both fields first. Each of the ten services moves to customer in its own pull request, and customer_name is removed last.

• D1: Remove customer_name only after every consumer reads customer. Approved by Elena Vasquez (Q1), following ADR-0012: Remove a response field only after its consumers have moved.

Touches

• Accounts API: returns customer alongside customer_name, then stops returning customer_name.

Ten services read GET /accounts/{id}:

• Billing: read customer.
• Orders: read customer.
• Checkout: read customer.
• Notifications: read customer.
• Search: read customer.
• Reporting: read customer.
• Support console: read customer.
• Admin: read customer.
• Payouts: read customer.
• Mobile BFF: read customer.

Risks

• A service that reads customer_name but is not on the list breaks when the field is removed. The list comes from 30 days of gateway access logs for GET /accounts/{id}, so a job that calls the endpoint through another path, or less often, may be missing.
• Mobile BFF caches account responses for older app versions. Its change has to ship before the removal reaches the cache.

Open questions

• Q1: When can customer_name be removed? Answered by Elena Vasquez: only after every consumer has migration evidence (D1).

Rejected alternatives

• A versioned endpoint, GET /v2/accounts/{id}. Rejected because both response shapes would have to be served for as long as any consumer stays on v1, and every consumer would still have to move.
• Removing customer_name on a fixed date after a deprecation notice. Rejected because a date says nothing about whether a consumer has moved (ADR-0012).