Enforce USDC-only membership mint configuration

backend/secretapi/README.md

@@ -139,7 +139,7 @@ Policy gates:
 - `SECRET_API_DOMAIN_NAME`
 - `SECRET_API_VERIFYING_CONTRACT`
 - `SECRET_API_MEMBERSHIP_CONTRACT`
-- `SECRET_API_MINT_CURRENCY` (default `USDC`)
+- `SECRET_API_MINT_CURRENCY` (must be `USDC` in v1)
 - `SECRET_API_MINT_AMOUNT_ATOMIC` (default `100000000`)
 - `SECRET_API_MINT_DECIMALS` (default `6`)
 

backend/secretapi/config.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"math/big"
 	"os"
 	"strconv"
 	"strings"
@@ -76,6 +77,17 @@ func (c Config) Validate() error {
 	if c.ChainID <= 0 {
 		return fmt.Errorf("SECRET_API_CHAIN_ID must be positive")
 	}
+	if strings.ToUpper(strings.TrimSpace(c.MintCurrency)) != "USDC" {
+		return fmt.Errorf("SECRET_API_MINT_CURRENCY must be USDC")
+	}
+	if c.MintDecimals != 6 {
+		return fmt.Errorf("SECRET_API_MINT_DECIMALS must be 6")
+	}
+	amountRaw := strings.TrimSpace(c.MintAmountAtomic)
+	amount, ok := new(big.Int).SetString(amountRaw, 10)
+	if !ok || amount.Sign() <= 0 {
+		return fmt.Errorf("SECRET_API_MINT_AMOUNT_ATOMIC must be a positive base-10 integer")
+	}
 	if c.WalletSessionTTL <= 0 {
 		return fmt.Errorf("SECRET_API_WALLET_SESSION_TTL_SECONDS must be positive")
 	}

backend/secretapi/config_test.go

@@ -31,3 +31,30 @@ func TestConfigValidateRejectsNonPositiveChainID(t *testing.T) {
 		t.Fatalf("expected chain id validation failure")
 	}
 }
+
+func TestConfigValidateRejectsNonUSDCCurrency(t *testing.T) {
+	t.Parallel()
+	cfg := loadConfig()
+	cfg.MintCurrency = "ETH"
+	if err := cfg.Validate(); err == nil {
+		t.Fatalf("expected mint currency validation failure")
+	}
+}
+
+func TestConfigValidateRejectsNonSixMintDecimals(t *testing.T) {
+	t.Parallel()
+	cfg := loadConfig()
+	cfg.MintDecimals = 18
+	if err := cfg.Validate(); err == nil {
+		t.Fatalf("expected mint decimals validation failure")
+	}
+}
+
+func TestConfigValidateRejectsInvalidMintAmount(t *testing.T) {
+	t.Parallel()
+	cfg := loadConfig()
+	cfg.MintAmountAtomic = "not-a-number"
+	if err := cfg.Validate(); err == nil {
+		t.Fatalf("expected mint amount validation failure")
+	}
+}

docs/api/secret-system.openapi.yaml

@@ -303,7 +303,7 @@ components:
           type: integer
         currency:
           type: string
-          enum: [USDC, ETH]
+          enum: [USDC]
         amount:
           type: string
         amount_atomic: