feat: update fee asset price calculation

Author: LHerskind

docs/docs-developers/docs/resources/migration_notes.md

@@ -9,6 +9,31 @@ Aztec is in full-speed development. Literally every version breaks compatibility
 
 ## TBD
 
+### [L1 Contracts] Fee asset pricing direction inverted
+
+The fee model now uses `ethPerFeeAsset` instead of the previous `feeAssetPerEth`. This change inverts how the exchange rate is represented: values now express how much ETH one fee asset (AZTEC) is worth, with 1e12 precision.
+
+**Key changes:**
+
+- `FeeHeader.feeAssetPerEth` → `FeeHeader.ethPerFeeAsset`
+- `RollupConfigInput` now requires `initialEthPerFeeAsset` parameter at deployment
+- Default value: `1e7` (0.00001 ETH per AZTEC)
+- Valid range: `100` (1e-10 ETH/AZTEC) to `1e11` (0.1 ETH/AZTEC)
+
+**New environment variable for node operators:**
+
+- `AZTEC_INITIAL_ETH_PER_FEE_ASSET` - Sets the initial ETH per fee asset price with 1e12 precision
+
+### [L1 Contracts] Fee asset price modifier now in basis points
+
+The `OracleInput.feeAssetPriceModifier` field now expects values in basis points (BPS) instead of the previous representation. The modifier is applied as a percentage change to the ETH/AZTEC price each checkpoint.
+
+**Key changes:**
+
+- Valid range: `-100` to `+100` BPS (±1% max change per checkpoint)
+- A value of `+100` increases the price by 1%, `-100` decreases by 1%
+- Validated by `MAX_FEE_ASSET_PRICE_MODIFIER_BPS = 100`
+
 ### [Aztec.js] Wallet batching now supports all methods
 
 The `BatchedMethod` type is now a discriminated union that ensures type safety: the `args` must match the specific method `name`. This prevents runtime errors from mismatched arguments.

docs/docs-network/operators/reference/changelog/v4.md

@@ -74,6 +74,20 @@ The `getL2Tips()` RPC endpoint now returns a restructured response with addition
 
 ## New features
 
+### Initial ETH per fee asset configuration
+
+A new environment variable `AZTEC_INITIAL_ETH_PER_FEE_ASSET` has been added to configure the initial exchange rate between ETH and the fee asset (AZTEC) at contract deployment. This value uses 1e12 precision.
+
+**Default**: `10000000` (0.00001 ETH per AZTEC)
+
+**Configuration:**
+
+```bash
+--initialEthPerFeeAsset <value>       ($AZTEC_INITIAL_ETH_PER_FEE_ASSET)
+```
+
+This replaces the previous hardcoded default and allows network operators to set the starting price point for the fee asset.
+
 ## Changed defaults
 
 ## Troubleshooting

l1-contracts/script/deploy/RollupConfiguration.sol

@@ -9,7 +9,7 @@ import {CheatDepositArgs} from "@aztec/mock/MultiAdder.sol";
 import {IRewardDistributor} from "@aztec/governance/interfaces/IRewardDistributor.sol";
 import {IBoosterCore} from "@aztec/core/reward-boost/RewardBooster.sol";
 import {SlasherFlavor} from "@aztec/core/interfaces/ISlasher.sol";
-import {EthValue} from "@aztec/core/libraries/rollup/FeeLib.sol";
+import {EthValue, EthPerFeeAssetE12} from "@aztec/core/libraries/rollup/FeeLib.sol";
 import {GenesisState, RollupConfigInput} from "@aztec/core/interfaces/IRollup.sol";
 import {Timestamp} from "@aztec/core/libraries/TimeLib.sol";
 import {RewardBoostConfig} from "@aztec/core/reward-boost/RewardBooster.sol";
@@ -133,6 +133,7 @@ contract RollupConfiguration is IRollupConfiguration, Test {
       exitDelaySeconds: vm.envUint("AZTEC_EXIT_DELAY_SECONDS"),
       version: 0, // Computed below
       provingCostPerMana: EthValue.wrap(vm.envUint("AZTEC_PROVING_COST_PER_MANA")),
+      initialEthPerFeeAsset: EthPerFeeAssetE12.wrap(vm.envUint("AZTEC_INITIAL_ETH_PER_FEE_ASSET")),
       rewardConfig: this.getRewardConfiguration(_rewardDistributor),
       rewardBoostConfig: this.getRewardBoostConfiguration(),
       stakingQueueConfig: this.getStakingQueueConfiguration(),

l1-contracts/src/core/Rollup.sol

@@ -10,7 +10,7 @@ import {
   PublicInputArgs,
   L1FeeData,
   ManaMinFeeComponents,
-  FeeAssetPerEthE9,
+  EthPerFeeAssetE12,
   CheckpointHeaderValidationFlags,
   FeeHeader,
   RollupConfigInput
@@ -519,7 +519,7 @@ contract Rollup is IStaking, IValidatorSelection, IRollup, RollupCore {
   }
 
   function getProvingCostPerManaInFeeAsset() external view override(IRollup) returns (FeeAssetValue) {
-    return FeeLib.getProvingCostPerMana().toFeeAsset(getFeeAssetPerEth());
+    return FeeLib.getProvingCostPerMana().toFeeAsset(getEthPerFeeAsset());
   }
 
   function getVersion() external view override(IHaveVersion) returns (uint256) {
@@ -656,12 +656,13 @@ contract Rollup is IStaking, IValidatorSelection, IRollup, RollupCore {
   }
 
   /**
-   * @notice  Gets the fee asset price as fee_asset / eth with 1e9 precision
+   * @notice  Gets the fee asset price as eth / fee_asset with 1e12 precision
+   *          Higher value = more expensive fee asset
    *
    * @return The fee asset price
    */
-  function getFeeAssetPerEth() public view override(IRollup) returns (FeeAssetPerEthE9) {
-    return FeeLib.getFeeAssetPerEthAtCheckpoint(STFLib.getStorage().tips.getPending());
+  function getEthPerFeeAsset() public view override(IRollup) returns (EthPerFeeAssetE12) {
+    return FeeLib.getEthPerFeeAssetAtCheckpoint(STFLib.getStorage().tips.getPending());
   }
 
   function getEpochForCheckpoint(uint256 _checkpointNumber) public view override(IRollup) returns (Epoch) {

l1-contracts/src/core/RollupCore.sol

@@ -311,7 +311,7 @@ contract RollupCore is EIP712("Aztec Rollup", "1"), Ownable, IStakingCore, IVali
 
     rollupStore.config.feeAssetPortal = IFeeJuicePortal(inbox.getFeeAssetPortal());
 
-    FeeLib.initialize(_config.manaTarget, _config.provingCostPerMana);
+    FeeLib.initialize(_config.manaTarget, _config.provingCostPerMana, _config.initialEthPerFeeAsset);
   }
 
   /**

l1-contracts/src/core/interfaces/IRollup.sol

@@ -8,7 +8,7 @@ import {IVerifier} from "@aztec/core/interfaces/IVerifier.sol";
 import {IInbox} from "@aztec/core/interfaces/messagebridge/IInbox.sol";
 import {IOutbox} from "@aztec/core/interfaces/messagebridge/IOutbox.sol";
 import {CheckpointLog, CompressedTempCheckpointLog} from "@aztec/core/libraries/compressed-data/CheckpointLog.sol";
-import {FeeAssetPerEthE9, EthValue, FeeAssetValue} from "@aztec/core/libraries/compressed-data/fees/FeeConfig.sol";
+import {EthPerFeeAssetE12, EthValue, FeeAssetValue} from "@aztec/core/libraries/compressed-data/fees/FeeConfig.sol";
 import {FeeHeader, L1FeeData} from "@aztec/core/libraries/compressed-data/fees/FeeStructs.sol";
 import {StakingQueueConfig} from "@aztec/core/libraries/compressed-data/StakingQueueConfig.sol";
 import {CompressedChainTips, ChainTips} from "@aztec/core/libraries/compressed-data/Tips.sol";
@@ -75,6 +75,7 @@ struct RollupConfigInput {
   uint256 exitDelaySeconds;
   uint32 version;
   EthValue provingCostPerMana;
+  EthPerFeeAssetE12 initialEthPerFeeAsset;
   RewardConfig rewardConfig;
   RewardBoostConfig rewardBoostConfig;
   StakingQueueConfig stakingQueueConfig;
@@ -199,7 +200,7 @@ interface IRollup is IRollupCore, IHaveVersion {
     returns (ManaMinFeeComponents memory);
   function getManaMinFeeAt(Timestamp _timestamp, bool _inFeeAsset) external view returns (uint256);
   function getL1FeesAt(Timestamp _timestamp) external view returns (L1FeeData memory);
-  function getFeeAssetPerEth() external view returns (FeeAssetPerEthE9);
+  function getEthPerFeeAsset() external view returns (EthPerFeeAssetE12);
 
   function getEpochForCheckpoint(uint256 _checkpointNumber) external view returns (Epoch);
   function canPruneAtTime(Timestamp _ts) external view returns (bool);

l1-contracts/src/core/libraries/Errors.sol

@@ -184,6 +184,7 @@ library Errors {
   error FeeLib__InvalidFeeAssetPriceModifier(); // 0xf2fb32ad
   error FeeLib__AlreadyPreheated();
   error FeeLib__InvalidManaLimit(uint256 maximum, uint256 provided);
+  error FeeLib__InvalidInitialEthPerFeeAsset(uint256 provided, uint256 minimum, uint256 maximum);
 
   // SignatureLib (duplicated)
   error SignatureLib__InvalidSignature(address, address); // 0xd9cbae6c

l1-contracts/src/core/libraries/compressed-data/fees/FeeConfig.sol

@@ -5,12 +5,28 @@ pragma solidity >=0.8.27;
 import {Math} from "@oz/utils/math/Math.sol";
 import {SafeCast} from "@oz/utils/math/SafeCast.sol";
 
+// Represents a value denominated in ETH (wei).
 type EthValue is uint256;
 
+// Represents a value denominated in the fee asset (e.g., AZTEC token).
 type FeeAssetValue is uint256;
 
-// Precision of 1e9
-type FeeAssetPerEthE9 is uint256;
+/*
+ * ETH per fee asset price with 1e12 precision.
+ * Higher stored value = more expensive fee asset (more ETH needed per 1 fee asset).
+ * actual_eth_per_fee_asset = stored_value / ETH_PER_FEE_ASSET_PRECISION
+ *
+ * We use 1e12 precision because:
+ * 1. The value must fit in 48 bits when compressed in FeeHeader (max ~2.8e14)
+ * 2. Higher precision allows representing very low prices (down to 1e-10 ETH)
+ * 3. Reduces rounding errors during ETH <-> FeeAsset conversions
+ *
+ * See FeeLib.sol for the MIN/MAX bounds and detailed documentation.
+ */
+type EthPerFeeAssetE12 is uint256;
+
+// Precision multiplier for ETH per fee asset. Divide stored value by this to get actual ratio.
+uint256 constant ETH_PER_FEE_ASSET_PRECISION = 1e12;
 
 function addEthValue(EthValue _a, EthValue _b) pure returns (EthValue) {
   return EthValue.wrap(EthValue.unwrap(_a) + EthValue.unwrap(_b));
@@ -31,18 +47,41 @@ struct FeeConfig {
   EthValue provingCostPerMana;
 }
 
+/// @notice Library for converting between ETH and fee asset values using the price oracle.
 library PriceLib {
-  function toEth(FeeAssetValue _feeAssetValue, FeeAssetPerEthE9 _feeAssetPerEth) internal pure returns (EthValue) {
+  /**
+   * @notice Converts a fee asset amount to its ETH equivalent.
+   * @dev ethValue = feeAssetAmount * ethPerFeeAsset / precision
+   * @param _feeAssetValue The amount in fee asset units
+   * @param _ethPerFeeAsset The current price (ETH per fee asset with 1e12 precision)
+   * @return The equivalent value in ETH (wei), rounded up
+   */
+  function toEth(FeeAssetValue _feeAssetValue, EthPerFeeAssetE12 _ethPerFeeAsset) internal pure returns (EthValue) {
     return EthValue.wrap(
       Math.mulDiv(
-        FeeAssetValue.unwrap(_feeAssetValue), 1e9, FeeAssetPerEthE9.unwrap(_feeAssetPerEth), Math.Rounding.Ceil
+        FeeAssetValue.unwrap(_feeAssetValue),
+        EthPerFeeAssetE12.unwrap(_ethPerFeeAsset),
+        ETH_PER_FEE_ASSET_PRECISION,
+        Math.Rounding.Ceil
       )
     );
   }
 
-  function toFeeAsset(EthValue _ethValue, FeeAssetPerEthE9 _feeAssetPerEth) internal pure returns (FeeAssetValue) {
+  /**
+   * @notice Converts an ETH amount to its fee asset equivalent.
+   * @dev feeAssetAmount = ethValue * precision / ethPerFeeAsset
+   * @param _ethValue The amount in ETH (wei)
+   * @param _ethPerFeeAsset The current price (ETH per fee asset with 1e12 precision)
+   * @return The equivalent value in fee asset units, rounded up
+   */
+  function toFeeAsset(EthValue _ethValue, EthPerFeeAssetE12 _ethPerFeeAsset) internal pure returns (FeeAssetValue) {
     return FeeAssetValue.wrap(
-      Math.mulDiv(EthValue.unwrap(_ethValue), FeeAssetPerEthE9.unwrap(_feeAssetPerEth), 1e9, Math.Rounding.Ceil)
+      Math.mulDiv(
+        EthValue.unwrap(_ethValue),
+        ETH_PER_FEE_ASSET_PRECISION,
+        EthPerFeeAssetE12.unwrap(_ethPerFeeAsset),
+        Math.Rounding.Ceil
+      )
     );
   }
 }

l1-contracts/src/core/libraries/compressed-data/fees/FeeStructs.sol

@@ -11,7 +11,7 @@ import {SafeCast} from "@oz/utils/math/SafeCast.sol";
   uint1 preHeat;
   uint63 proverCost; Max value: 9.2233720369E18
   uint64 congestionCost;
-  uint48 feeAssetPriceNumerator;
+  uint48 ethPerFeeAsset;
   uint48 excessMana;
   uint32 manaUsed;
 }*/
@@ -20,7 +20,7 @@ type CompressedFeeHeader is uint256;
 struct FeeHeader {
   uint256 excessMana;
   uint256 manaUsed;
-  uint256 feeAssetPriceNumerator;
+  uint256 ethPerFeeAsset;
   uint256 congestionCost;
   uint256 proverCost;
 }
@@ -86,7 +86,7 @@ library FeeHeaderLib {
     return (CompressedFeeHeader.unwrap(_compressedFeeHeader) >> 32) & MASK_48_BITS;
   }
 
-  function getFeeAssetPriceNumerator(CompressedFeeHeader _compressedFeeHeader) internal pure returns (uint256) {
+  function getEthPerFeeAsset(CompressedFeeHeader _compressedFeeHeader) internal pure returns (uint256) {
     return (CompressedFeeHeader.unwrap(_compressedFeeHeader) >> 80) & MASK_48_BITS;
   }
 
@@ -103,7 +103,7 @@ library FeeHeaderLib {
     uint256 value = 0;
     value |= uint256(_feeHeader.manaUsed.toUint32());
     value |= uint256(_feeHeader.excessMana.toUint48()) << 32;
-    value |= uint256(_feeHeader.feeAssetPriceNumerator.toUint48()) << 80;
+    value |= uint256(_feeHeader.ethPerFeeAsset.toUint48()) << 80;
     value |= uint256(_feeHeader.congestionCost.toUint64()) << 128;
 
     uint256 proverCost = uint256(_feeHeader.proverCost.toUint64());
@@ -123,7 +123,7 @@ library FeeHeaderLib {
     value >>= 32;
     uint256 excessMana = value & MASK_48_BITS;
     value >>= 48;
-    uint256 feeAssetPriceNumerator = value & MASK_48_BITS;
+    uint256 ethPerFeeAsset = value & MASK_48_BITS;
     value >>= 48;
     uint256 congestionCost = value & MASK_64_BITS;
     value >>= 64;
@@ -132,7 +132,7 @@ library FeeHeaderLib {
     return FeeHeader({
       manaUsed: uint256(manaUsed),
       excessMana: uint256(excessMana),
-      feeAssetPriceNumerator: uint256(feeAssetPriceNumerator),
+      ethPerFeeAsset: uint256(ethPerFeeAsset),
       congestionCost: uint256(congestionCost),
       proverCost: uint256(proverCost)
     });