Fix Sell Max showing entered fiat value in crypto field

CHANGELOG.md

@@ -2,8 +2,9 @@
 
 ## Unreleased (develop)
 
-- fixed: NYM max swaps from EVM wallets now report the correct limit error instead of an unsupported-route error (edge-exchange-plugins 2.52.1).
 - changed: Sign MoonPay buy/sell widget URLs and bind them to the customer's IP via the info server, for MoonPay's on-ramp IP-matching security upgrade.
+- fixed: NYM max swaps from EVM wallets now report the correct limit error instead of an unsupported-route error (edge-exchange-plugins 2.52.1).
+- fixed: Tapping Max on the Sell scene no longer briefly shows the entered fiat amount in the crypto field while the max is being calculated.
 
 ## 4.50.0 (2026-07-21)
 

src/components/scenes/RampCreateScene.tsx

@@ -114,6 +114,14 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
     null
   )
   const [pendingMaxNav, setPendingMaxNav] = useState(false)
+  // A monotonic id for the in-flight max flow, bumped synchronously (unlike the
+  // `pendingMaxNav` state). handleMaxPress captures the id for its request; any
+  // later Max, or a wallet/fiat switch that cancels the flow, increments it.
+  // The async sell max handler applies its result only if its captured id is
+  // still current, so a stale in-flight getMaxSpendExchangeAmount (e.g. for a
+  // since-switched asset, or a superseded earlier request) is discarded. A
+  // plain boolean cannot distinguish which request is current.
+  const maxRequestIdRef = React.useRef(0)
   const hasAppliedInitialAmount = React.useRef(false)
 
   // Selected currencies
@@ -568,6 +576,7 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
       }
 
       // Clear amount and max state when switching crypto assets in sell mode
+      maxRequestIdRef.current += 1
       setPendingMaxNav(false)
       if (direction === 'sell') {
         setAmountQuery({ empty: true })
@@ -585,6 +594,7 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
 
   const handleFiatDropdown = useHandler(async () => {
     if (account == null) return
+    maxRequestIdRef.current += 1
     setPendingMaxNav(false)
     const result = await Airship.show<GuiFiatType>(bridge => (
       <FiatListModal bridge={bridge} />
@@ -660,23 +670,36 @@ export const RampCreateScene: React.FC<Props> = (props: Props) => {
       return
     }
 
-    // Trigger a transient max flow: request quotes with {max:true} and auto-navigate when ready
+    // Trigger a transient max flow: request quotes and auto-navigate when ready.
+    // Do NOT flip `lastUsedInput` before the amount query is set to the max
+    // marker. For sell, computing the max is async; if `lastUsedInput` became
+    // 'crypto' while `amountQuery` still held the previously entered fiat
+    // amount, `displayCryptoAmount` would render that fiat value in the crypto
+    // field (e.g. "100 USD" shown as "100 BTC"). Set the max amount query first
+    // so the display memos take their max branch, then set the input type.
+    const maxRequestId = ++maxRequestIdRef.current
     setPendingMaxNav(true)
-    setLastUsedInput(direction === 'buy' ? 'fiat' : 'crypto')
 
     if (direction === 'sell') {
       const maxSpendExchangeAmount = await getMaxSpendExchangeAmount(
         selectedWallet,
         selectedCrypto.tokenId,
         denomination
       )
+      // Discard the result if a newer Max, or a wallet/fiat switch that
+      // cancelled the flow, superseded this request while
+      // getMaxSpendExchangeAmount was in flight: this (now stale) max belongs
+      // to the previously selected asset.
+      if (maxRequestIdRef.current !== maxRequestId) return
       setAmountQuery({
         maxExchangeAmount: maxSpendExchangeAmount
       })
+      setLastUsedInput('crypto')
     } else {
       setAmountQuery({
         max: true
       })
+      setLastUsedInput('fiat')
     }
   })