fix: update production app configuration

docs/protocols/payments/apple-iap-protocol.md

@@ -14,6 +14,7 @@ Protocol verification status:
 
 - Current strategy: additive evolution (`backward-compatible`).
 - Breaking change requires explicit migration + rollback notes (`requires-migration`).
+- Apple IAP environment is auto-detected from verified Apple transaction payloads; the verify API is not split by Sandbox/Production.
 
 ## Route overview
 
@@ -70,7 +71,6 @@ Verify and grant credits for an Apple IAP transaction.
 |---|---:|---|
 | `PAYMENT_PRODUCT_NOT_FOUND` | 404 | `productCode` does not exist or is not enabled |
 | `PAYMENT_PRODUCT_MISMATCH` | 422 | Client product ID does not match backend/Apple verification result |
-| `PAYMENT_ENVIRONMENT_MISMATCH` | 422 | Transaction environment (Sandbox/Production) does not match server environment |
 | `PAYMENT_TRANSACTION_INVALID` | 422 | Apple signed transaction invalid, signature verification failed, or payload malformed |
 | `PAYMENT_TRANSACTION_REVOKED` | 409 | Transaction has been revoked or refunded, grant not allowed |
 | `PAYMENT_TRANSACTION_CONFLICT` | 409 | Transaction already processed by another user or in conflicting state |
@@ -119,6 +119,14 @@ product_mappings:
 - Backend tracks purchase via `register_bonus_claims.has_purchased_starter_pack`
 - If already purchased, returns `PAYMENT_STARTER_PACK_INELIGIBLE` (409)
 
+## Environment handling
+
+- `signedTransactionInfo` is verified server-side and its Apple-provided `environment` field is the source of truth.
+- Valid environments are `Sandbox` and `Production`.
+- TestFlight and App Review Sandbox transactions are accepted when Apple signs them as `Sandbox`.
+- App Store Production transactions are accepted when Apple signs them as `Production`.
+- Backend configuration defaults to `apple_iap.environment=auto`; it must not force all verifications into one Apple environment.
+
 ## Ledger integration
 
 - Successful purchases create a ledger entry with: