fix(sdk-coin-flrp): add correct C-chain atomic import gas formula

modules/sdk-coin-flrp/src/lib/index.ts

@@ -1,7 +1,7 @@
 import Utils from './utils';
 export * from './iface';
 export { KeyPair } from './keyPair';
-export { Utils };
+export { Utils, calcImportCGas, calcImportCFee, ATOMIC_TX_BASE_COST, COST_PER_SIGNATURE, COST_PER_BYTE } from './utils';
 export { TransactionBuilderFactory } from './transactionBuilderFactory';
 export { TransactionBuilder } from './transactionBuilder';
 export { Transaction } from './transaction';

modules/sdk-coin-flrp/src/lib/utils.ts

@@ -596,5 +596,53 @@ export class Utils implements BaseUtils {
   }
 }
 
+/**
+ * Coreth (C-chain EVM) atomic import gas cost constants.
+ * Source: coreth plugin/evm/atomic/params.go and avalanchego params.
+ */
+export const ATOMIC_TX_BASE_COST = 10_000n; // AtomicTxBaseCost fixed overhead
+export const COST_PER_SIGNATURE = 1_000n; // gas per signature slot in the tx
+export const COST_PER_BYTE = 1n; // gas per byte of serialized tx
+
+/**
+ * Compute the gas units required for a C-chain atomic import transaction.
+ *
+ * Formula (from coreth import_tx.go):
+ *   gas = txByteLen × CTxBytesGas + numSigs × CCostPerSignature + AtomicTxBaseCost
+ *
+ * @param txByteLen - serialized byte length of the transaction
+ * @param numSigs   - number of signature slots in the transaction
+ * @returns gas units as bigint
+ */
+export function calcImportCGas(txByteLen: number, numSigs: number): bigint {
+  return BigInt(txByteLen) * COST_PER_BYTE + BigInt(numSigs) * COST_PER_SIGNATURE + ATOMIC_TX_BASE_COST;
+}
+
+/**
+ * Compute the fee in nFLR for a C-chain atomic import transaction.
+ *
+ * Applies a multiplier to the base gas estimate to pad against base-fee
+ * volatility between the time the transaction is built and when it is
+ * broadcast.  A value of 2n (2×) is the recommended default; callers may
+ * pass a smaller multiplier (minimum 1n) if they prefer a tighter bound.
+ *
+ * @param txByteLen       - serialized byte length of the transaction
+ * @param numSigs         - number of signature slots
+ * @param baseFeeNanoFlr  - current C-chain base fee in nFLR (e.g. 500_000_000_000n for 500 gwei)
+ * @param multiplier      - fee multiplier for volatility padding (default 2n)
+ * @returns fee in nFLR as bigint
+ */
+export function calcImportCFee(
+  txByteLen: number,
+  numSigs: number,
+  baseFeeNanoFlr: bigint,
+  multiplier = 2n
+): bigint {
+  if (multiplier < 1n) {
+    throw new Error('multiplier must be >= 1');
+  }
+  return calcImportCGas(txByteLen, numSigs) * baseFeeNanoFlr * multiplier;
+}
+
 const utils = new Utils();
 export default utils;

modules/sdk-coin-flrp/test/unit/lib/utils.ts

@@ -952,3 +952,65 @@ describe('Utils', function () {
     });
   });
 });
+
+import { calcImportCGas, calcImportCFee, ATOMIC_TX_BASE_COST, COST_PER_SIGNATURE, COST_PER_BYTE } from '../../../src/lib/utils';
+
+describe('calcImportCGas / calcImportCFee', function () {
+  describe('calcImportCGas', function () {
+    it('should compute gas for the ticket example (311 bytes, 1 sig)', function () {
+      // Expected: 311 * 1 + 1 * 1000 + 10000 = 11311
+      assert.strictEqual(calcImportCGas(311, 1), 11311n);
+    });
+
+    it('should include AtomicTxBaseCost even for zero bytes and zero sigs', function () {
+      assert.strictEqual(calcImportCGas(0, 0), ATOMIC_TX_BASE_COST);
+    });
+
+    it('should scale with byte count', function () {
+      // 100 bytes, 2 sigs: 100 + 2000 + 10000 = 12100
+      assert.strictEqual(calcImportCGas(100, 2), 12100n);
+    });
+
+    it('should use exported constants', function () {
+      assert.strictEqual(ATOMIC_TX_BASE_COST, 10_000n);
+      assert.strictEqual(COST_PER_SIGNATURE, 1_000n);
+      assert.strictEqual(COST_PER_BYTE, 1n);
+    });
+  });
+
+  describe('calcImportCFee', function () {
+    it('should reproduce the ticket failing-fee with 1× multiplier', function () {
+      // 5700 gas (old estimate) * 500 gwei = 2,850,000 nFLR (insufficient)
+      // Correct: 11311 gas * 500 gwei * 1x = 5,655,500 nFLR
+      const baseFee = 500_000_000_000n; // 500 gwei in nFLR (1 gwei = 1e9 nFLR? no — actually nFLR = wei for FLR)
+      // On Flare: 1 gwei = 1e9 nwei but nFLR is 1e-9 FLR. baseFee in nFLR = baseFee * 1 (gwei = nFLR units).
+      // The ticket says 500 gwei base fee => 500*1e9 nFLR/gas if we treat gwei as wei.
+      // But the ticket says 5700 gas * 500 gwei = 2,850,000 nFLR, so 1 gwei = 500 nFLR/5700 * 5700 →
+      // actually: 5700 * 500 = 2,850,000 nFLR means baseFee is 500 nFLR/gas = 500 gwei where 1 gwei = 1 nFLR.
+      // Wait: nFLR = nano-FLR. 1 FLR = 1e9 nFLR. 1 gwei = 1e9 wei but for FLR we use nFLR as the smallest unit.
+      // So 500 gwei (= 500 * 1e9 nwei) but FLR's base denom is nFLR. The ticket says 5700 * 500 = 2.85M nFLR.
+      // So the baseFee passed to the builder is 500 (nFLR per gas unit).
+      const baseFeePerGas = 500n; // 500 nFLR/gas
+      const fee = calcImportCFee(311, 1, baseFeePerGas, 1n);
+      assert.strictEqual(fee, 11311n * 500n);
+    });
+
+    it('should double the fee with default 2× multiplier', function () {
+      const baseFeePerGas = 500n;
+      const feeX1 = calcImportCFee(311, 1, baseFeePerGas, 1n);
+      const feeX2 = calcImportCFee(311, 1, baseFeePerGas);
+      assert.strictEqual(feeX2, feeX1 * 2n);
+    });
+
+    it('should throw for multiplier < 1', function () {
+      assert.throws(() => calcImportCFee(311, 1, 500n, 0n), /multiplier must be >= 1/);
+    });
+
+    it('the 2× fee should comfortably cover the ticket scenario (500 gwei base, 311B, 1 sig)', function () {
+      const baseFeePerGas = 500n;
+      const paddedFee = calcImportCFee(311, 1, baseFeePerGas, 2n);
+      const requiredFee = 11311n * 500n; // minimum required by the node
+      assert.ok(paddedFee >= requiredFee, `padded fee ${paddedFee} should be >= required ${requiredFee}`);
+    });
+  });
+});

modules/statics/src/networks.ts

@@ -41,6 +41,8 @@ export interface FlareNetwork extends BaseNetwork {
   addSubnetValidatorFee?: string;
   addSubnetDelegatorFee?: string;
   xChainBlockchainID?: string;
+  /** Fee multiplier applied to C-chain atomic import gas estimates to buffer base-fee volatility (default 2). */
+  importFeeMultiplier?: number;
 }
 
 import { CoinFamily } from './base';
@@ -2367,6 +2369,7 @@ export class FlareP extends Mainnet implements FlareNetwork {
   txFee = '200000'; // FLR P-chain import requires higher fee than base txFee
   baseTxFee = '1000000';
   maxImportFee = '10000000'; // defaults
+  importFeeMultiplier = 2; // 2× buffer for C-chain base-fee volatility
   createAssetTxFee = '1000000';
   createSubnetTx = '100000000'; // defaults
   transformSubnetTxFee = '100000000';
@@ -2403,6 +2406,7 @@ export class FlarePTestnet extends Testnet implements FlareNetwork {
   txFee = '200000'; // FLR P-chain import requires higher fee than base txFee
   baseTxFee = '1000000';
   maxImportFee = '10000000'; // defaults
+  importFeeMultiplier = 2; // 2× buffer for C-chain base-fee volatility
   createAssetTxFee = '1000000';
   createSubnetTx = '100000000'; // defaults
   transformSubnetTxFee = '100000000';