Reduce the EVM baseline transfer fee to 90 eHMND

crates/humanode-runtime/src/constants.rs

@@ -110,11 +110,16 @@ pub mod evm_fees {
     /// The amount of fee per gas unit.
     /// Comes from the following rationale:
     /// - a simple transfer costs 21000 gas
-    /// - we want the cost of this transfer to be around ~134 HMND
-    /// - so we must charge about 134 * 10^18 / 21000 fee per a unit of gas
-    /// The value below is a nice round number that fits the requirements outlined above:
-    /// the base value of `100_000_000_000_000` prices a single transfer at ~2 HMND.
-    pub const FEE_PER_GAS: u128 = 67 * 100_000_000_000_000;
+    /// - we want the cost of this transfer to be around ~90 HMND
+    /// - so we must charge about 90 * 10^18 / 21000 fee per a unit of gas
+    /// The value below is a nice round number that fits the requirements outlined above.
+    ///
+    /// Note: this value is intentionally decoupled from the weight-based fee
+    /// (see [`crate::constants::fees::WEIGHT_TO_FEE`]): pricing the gas-to-weight mapping of the
+    /// same transfer through the weight-based fee would give ~135 HMND, but Ethereum transactions
+    /// pay their fees through the EVM gas accounting and not through the transaction payment,
+    /// so we set the gas price to target the fee we actually want.
+    pub const FEE_PER_GAS: u128 = 4_300_000_000_000_000;
 
     /// The max proof size ratio per block.
     /// Set to the zero as humanode is solo chain. Otherwise, additional used gas has

crates/humanode-runtime/src/tests/fees.rs

@@ -223,8 +223,13 @@ fn simple_balances_transfer_keep_alive() {
     })
 }
 
-/// A test that validates that a simple EVM balance transfer with a keep alive costs 134 HMND.
+/// A test that validates the substrate-side fee estimate of a simple EVM balance transfer.
 /// Computes the fee via [`TransactionPayment::query_call_info`].
+///
+/// This estimate is weight-based and is intentionally decoupled from the actual gas-based
+/// charge (~90 HMND, see [`constants::evm_fees::FEE_PER_GAS`]): Ethereum transactions do not pay
+/// their fees through the transaction payment, so this value is what substrate-side tooling
+/// would display, not what is charged.
 #[test]
 fn simple_evm_transaction_via_query_call_info() {
     // Build the state from the config.
@@ -258,8 +263,9 @@ fn simple_evm_transaction_via_query_call_info() {
             }),
         });
 
-        // The expected fee that we aim to target: 134 HMND.
-        let expected_fee = 134 * ONE_BALANCE_UNIT;
+        // The weight-derived fee estimate: ~135 HMND (21000 gas mapped to weight and priced
+        // via `WEIGHT_TO_FEE`). This is not what an EVM transaction actually pays.
+        let expected_fee = 135 * ONE_BALANCE_UNIT;
 
         // The tolerance within which the actual fee is allowed to be around the expected fee.
         let epsilon = expected_fee / 10;
@@ -268,7 +274,7 @@ fn simple_evm_transaction_via_query_call_info() {
     })
 }
 
-/// A test that validates that a simple EVM balance transfer with a keep alive costs 134 HMND.
+/// A test that validates that a simple EVM balance transfer with a keep alive costs 90 HMND.
 /// Computes the fee via an estimate EVM runner invocation.
 #[test]
 fn simple_evm_transaction_via_runner_estimate() {
@@ -334,8 +340,8 @@ fn simple_evm_transaction_via_runner_estimate() {
             }
         );
 
-        // The expected fee that we aim to target: 134 HMND.
-        let expected_fee = 134 * ONE_BALANCE_UNIT;
+        // The expected fee that we aim to target: 90 HMND.
+        let expected_fee = 90 * ONE_BALANCE_UNIT;
 
         // The tolerance within which the actual fee is allowed to be around the expected fee.
         let epsilon = expected_fee / 10;

utils/e2e-tests/ts/tests/base/rpc/eth.ts

@@ -43,7 +43,7 @@ describe("eth rpc", () => {
   describe("fee", () => {
     describe("when transferring 1 eHMND", () => {
       const transferValue = ethers.parseEther("1");
-      const expectedFee = ethers.parseEther("134");
+      const expectedFee = ethers.parseEther("90");
       const tolerance = expectedFee / 10n;
 
       it("is within the tolerance around the expected cost", async () => {