diff --git a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/bitcoinNative/BitcoinNativeAssetBalance.kt b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/bitcoinNative/BitcoinNativeAssetBalance.kt
index 508e2968..c0247eaf 100644
--- a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/bitcoinNative/BitcoinNativeAssetBalance.kt
+++ b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/bitcoinNative/BitcoinNativeAssetBalance.kt
@@ -59,8 +59,9 @@ class BitcoinNativeAssetBalance(
         chainAsset: Chain.Asset,
         accountId: AccountId,
     ): Flow<TransferableBalanceUpdatePoint> {
-        // Not on the critical sync path (mirrors TronNativeAssetBalance/EvmNativeAssetBalance) - out of scope for Phase 4.
-        TODO("Not yet implemented")
+        // Only ever invoked from RealCrossChainTransactor (XCM arrival detection), which is Substrate-only -
+        // Bitcoin can never be an XCM cross-chain destination, so this is intentionally never reachable.
+        throw UnsupportedOperationException("Bitcoin does not support XCM-style balance update points")
     }
 
     override suspend fun startSyncingBalance(
diff --git a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/evmNative/EvmNativeAssetBalance.kt b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/evmNative/EvmNativeAssetBalance.kt
index 2b117b6f..cf8a9e8e 100644
--- a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/evmNative/EvmNativeAssetBalance.kt
+++ b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/evmNative/EvmNativeAssetBalance.kt
@@ -63,7 +63,10 @@ class EvmNativeAssetBalance(
         chainAsset: Chain.Asset,
         accountId: AccountId,
     ): Flow<TransferableBalanceUpdatePoint> {
-        TODO("Not yet implemented")
+        // Only ever invoked from RealCrossChainTransactor (XCM arrival detection), which is Substrate-only -
+        // an EVM chain's native asset can never be an XCM cross-chain destination, so this is intentionally
+        // never reachable.
+        throw UnsupportedOperationException("EVM native assets do not support XCM-style balance update points")
     }
 
     override suspend fun startSyncingBalance(
diff --git a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/trc20/Trc20AssetBalance.kt b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/trc20/Trc20AssetBalance.kt
index 2826a3d1..e4a1737b 100644
--- a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/trc20/Trc20AssetBalance.kt
+++ b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/trc20/Trc20AssetBalance.kt
@@ -62,8 +62,9 @@ class Trc20AssetBalance(
         chainAsset: Chain.Asset,
         accountId: AccountId,
     ): Flow<TransferableBalanceUpdatePoint> {
-        // Not on the critical sync path (mirrors EvmNativeAssetBalance) - out of scope for Phase 1 read-only support.
-        TODO("Not yet implemented")
+        // Only ever invoked from RealCrossChainTransactor (XCM arrival detection), which is Substrate-only -
+        // Tron/TRC20 can never be an XCM cross-chain destination, so this is intentionally never reachable.
+        throw UnsupportedOperationException("TRC20 does not support XCM-style balance update points")
     }
 
     override suspend fun startSyncingBalance(
diff --git a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/tronNative/TronNativeAssetBalance.kt b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/tronNative/TronNativeAssetBalance.kt
index d65c3a6f..fd49f092 100644
--- a/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/tronNative/TronNativeAssetBalance.kt
+++ b/feature-wallet-impl/src/main/java/io/novafoundation/nova/feature_wallet_impl/data/network/blockchain/assets/balances/tronNative/TronNativeAssetBalance.kt
@@ -59,9 +59,9 @@ class TronNativeAssetBalance(
         chainAsset: Chain.Asset,
         accountId: AccountId,
     ): Flow<TransferableBalanceUpdatePoint> {
-        // Not on the critical sync path (mirrors EvmNativeAssetBalance, which also leaves this unimplemented) -
-        // out of scope for Phase 1 read-only support.
-        TODO("Not yet implemented")
+        // Only ever invoked from RealCrossChainTransactor (XCM arrival detection), which is Substrate-only -
+        // Tron can never be an XCM cross-chain destination, so this is intentionally never reachable.
+        throw UnsupportedOperationException("Tron does not support XCM-style balance update points")
     }
 
     override suspend fun startSyncingBalance(