feat(config): implement fail-safe dual domain separators for V2 receipts

  - Update indexer-service and tap-agent to use correct V2 verifier addresses
  - Add strict validation: V2 address required when horizon.enabled=true
  - Implement graceful fallback when Horizon is disabled

Author: neithanmo

crates/service/src/service.rs

@@ -101,7 +101,13 @@ pub async fn run() -> anyhow::Result<()> {
 
     let domain_separator_v2 = tap_eip712_domain(
         config.blockchain.chain_id as u64,
-        config.blockchain.receipts_verifier_address,
+        if config.horizon.enabled {
+            config.blockchain.receipts_verifier_address_v2
+                .expect("receipts_verifier_address_v2 is required when Horizon is enabled")
+        } else {
+            config.blockchain.receipts_verifier_address_v2
+                .unwrap_or(config.blockchain.receipts_verifier_address)
+        },
         tap_core::TapVersion::V2,
     );
     let chain_id = config.blockchain.chain_id as u64;

crates/tap-agent/src/lib.rs

@@ -34,7 +34,13 @@ pub static EIP_712_DOMAIN: LazyLock<Eip712Domain> = LazyLock::new(|| {
 pub static EIP_712_DOMAIN_V2: LazyLock<Eip712Domain> = LazyLock::new(|| {
     tap_eip712_domain(
         CONFIG.blockchain.chain_id as u64,
-        CONFIG.blockchain.receipts_verifier_address,
+        if CONFIG.horizon.enabled {
+            CONFIG.blockchain.receipts_verifier_address_v2
+                .expect("receipts_verifier_address_v2 is required when Horizon is enabled")
+        } else {
+            CONFIG.blockchain.receipts_verifier_address_v2
+                .unwrap_or(CONFIG.blockchain.receipts_verifier_address)
+        },
         tap_core::TapVersion::V2,
     )
 });