Apply Solana→EVM fee multiplier workaround for SDK under-reporting (#3701)

Author: atn4z7

packages/core-mobile/app/new/features/swap/hooks/useFeeEstimation.ts

@@ -17,16 +17,23 @@ import { buildFeeOptions } from './useMaxSwapAmount/utils'
  * points). Use gasSafetyBps for the Max button (needs extra headroom); omit it
  * for balance validation (standard estimate is sufficient).
  *
+ * solanaToEvmFeeMultiplier: temporary workaround for the SDK under-reporting
+ * fees on Solana→EVM routes. Multiplied into the raw fee before gasSafetyBps
+ * is applied. Use 12 for validation, 15 for Max. No effect on other routes.
+ *
  * Returns gasFee as undefined while the estimate is loading.
  */
 export const useFeeEstimation = ({
   quote,
   fromNetwork,
-  gasSafetyBps = 0
+  gasSafetyBps = 0,
+  solanaToEvmFeeMultiplier = 1
 }: {
   quote: Quote | null
   fromNetwork?: NetworkWithCaip2ChainId
   gasSafetyBps?: number
+  /** Temporary workaround: SDK under-reports fees on Solana→EVM routes */
+  solanaToEvmFeeMultiplier?: number
 }): {
   gasFee: bigint | undefined
   rawGasFee: bigint | undefined
@@ -47,18 +54,26 @@ export const useFeeEstimation = ({
       ReactQueryKeys.FUSION_SWAP_FEE_ESTIMATE,
       quote?.id,
       feeOptions.feeUnitsMarginBps,
-      gasSafetyBps
+      gasSafetyBps,
+      solanaToEvmFeeMultiplier
     ],
     queryFn: quote
       ? async () => {
           const { totalUpfrontFee } = await FusionService.estimateNativeFee(
             quote,
             feeOptions
           )
+          const isSolanaToEvm =
+            quote.sourceChain.chainId.startsWith('solana:') &&
+            quote.targetChain.chainId.startsWith('eip155:')
+          const adjustedFee =
+            isSolanaToEvm && solanaToEvmFeeMultiplier > 1
+              ? totalUpfrontFee * BigInt(solanaToEvmFeeMultiplier)
+              : totalUpfrontFee
           const buffered =
             gasSafetyBps > 0
-              ? (totalUpfrontFee * (10000n + BigInt(gasSafetyBps))) / 10000n
-              : totalUpfrontFee
+              ? (adjustedFee * (10000n + BigInt(gasSafetyBps))) / 10000n
+              : adjustedFee
           return { raw: totalUpfrontFee, buffered }
         }
       : skipToken,

packages/core-mobile/app/new/features/swap/hooks/useFeeValidation/index.ts

@@ -111,7 +111,12 @@ export const useFeeValidation = ({
     rawGasFee,
     error,
     isFetching
-  } = useFeeEstimation({ quote, fromNetwork, gasSafetyBps })
+  } = useFeeEstimation({
+    quote,
+    fromNetwork,
+    gasSafetyBps,
+    solanaToEvmFeeMultiplier: 12
+  })
 
   const validationError = useMemo(() => {
     if (error && !isFetching) {

packages/core-mobile/app/new/features/swap/hooks/useMaxSwapAmount/index.ts

@@ -148,7 +148,8 @@ export const useMaxSwapAmount = ({
   } = useFeeEstimation({
     quote: preQuote,
     fromNetwork,
-    gasSafetyBps: maxAmountGasSafetyBps
+    gasSafetyBps: maxAmountGasSafetyBps,
+    solanaToEvmFeeMultiplier: 15
   })
 
   const additiveFeeForMax = resolveAdditiveFeeForMax(