fix

src/widgets/send-modal/model/sendTypes.ts

@@ -94,6 +94,28 @@ export const CHAIN_CONFIG: Record<Chain, ChainConfig> = {
   },
 }
 
+// ─── Network-fee estimates ───────────────────────────────────────────────────
+// Rough, static estimates of the network fee for a single transfer, expressed in
+// the chain's native coin (human units). Used to (a) reserve the fee in the "Макс"
+// button for native sends and (b) show an approximate cost in the send modal.
+// Real fees are computed by the backend at broadcast time — these are intentionally
+// conservative placeholders and can be swapped for a live estimate endpoint later.
+
+export const NETWORK_FEE_ESTIMATE: Record<Chain, Record<FeeTier, string>> = {
+  ETH: { slow: '0.00021',  normal: '0.00042',  fast: '0.00084'  },
+  BSC: { slow: '0.00021',  normal: '0.00021',  fast: '0.00021'  },
+  BTC: { slow: '0.00002',  normal: '0.00007',  fast: '0.0002'   },
+  TRX: { slow: '1.1',      normal: '1.1',      fast: '1.1'      },
+  SOL: { slow: '0.000005', normal: '0.000005', fast: '0.000005' },
+}
+
+/** Estimated native-coin network fee for a chain at the given speed tier.
+ *  Chains without fee tiers ignore `tier` and always use the `normal` value. */
+export function estimateNetworkFee(chain: Chain, tier: FeeTier): string {
+  const perTier = NETWORK_FEE_ESTIMATE[chain]
+  return CHAIN_CONFIG[chain].hasFeeTier ? perTier[tier] : perTier.normal
+}
+
 // ─── Wallet ticker → chain mapping (for TokenTable integration) ──────────────
 // ARB is an ERC-20 on Ethereum, not a separate chain.
 

src/widgets/send-modal/ui/SendModal.module.css

@@ -328,6 +328,31 @@
   text-decoration: underline;
 }
 
+/* ─── Network fee ───────────────────────────── */
+
+.feeRow {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  padding: 12px 14px;
+  margin-bottom: 12px;
+  background: var(--glass-bg);
+  border: 1px solid var(--glass-border);
+  border-radius: 12px;
+  font-size: 13px;
+}
+
+.feeLabel {
+  color: var(--text-secondary);
+}
+
+.feeValue {
+  font-family: var(--font-mono);
+  font-weight: 600;
+  color: var(--text-primary);
+}
+
 /* ─── Error message ─────────────────────────── */
 
 .errorMsg {

src/widgets/send-modal/ui/SendModal.tsx

@@ -1,7 +1,8 @@
 import { useState, useEffect } from 'react'
 import { useSendWallet } from '@features/wallet'
 import { getCoinIcon } from '@shared/assets/coins'
-import { CHAIN_CONFIG, CHAIN_TOKENS, type Chain, type FeeTier } from '../model/sendTypes'
+import { toBaseUnits, fromBaseUnits } from '@shared/lib/utils/baseUnits'
+import { CHAIN_CONFIG, CHAIN_TOKENS, estimateNetworkFee, type Chain, type FeeTier } from '../model/sendTypes'
 import styles from './SendModal.module.css'
 
 export interface SendModalToken {
@@ -53,11 +54,30 @@ export function SendModal({ open, onClose, network, tokens = [], initialToken =
   const mutation = useSendWallet()
 
   const speedLabel  = SPEEDS.find((s) => s.value === speed)?.label ?? 'Нормально'
-  const tokenLabel  = selectedToken === '' ? cfg.nativeSymbol : selectedToken
+  const isNative    = selectedToken === ''
+  const tokenLabel  = isNative ? cfg.nativeSymbol : selectedToken
   const walletMatch = tokens.find(
-    (t) => t.ticker === (selectedToken === '' ? cfg.nativeSymbol : selectedToken),
+    (t) => t.ticker === (isNative ? cfg.nativeSymbol : selectedToken),
   )
 
+  // Estimated native-coin network fee for the current chain/speed. Shown at the
+  // bottom of the modal and reserved by "Макс" for native sends.
+  const networkFee = estimateNetworkFee(network, speed)
+
+  // Max amount the user can send. For native coins the fee is paid from the same
+  // balance, so reserve it (balance − fee, floored at 0). Token sends pay the fee
+  // in the native coin, so the full token balance stays sendable.
+  function maxSendable(): string {
+    if (!walletMatch) return ''
+    if (!isNative) return walletMatch.bal
+    const dec = cfg.nativeDecimals
+    const balBase = BigInt(toBaseUnits(walletMatch.bal, dec))
+    const feeBase = BigInt(toBaseUnits(networkFee, dec))
+    const net = balBase > feeBase ? balBase - feeBase : 0n
+    return fromBaseUnits(net.toString(), dec)
+  }
+  const maxAmount = maxSendable()
+
   useEffect(() => { setSelectedToken(initialToken) }, [initialToken])
   useEffect(() => { setSelectedToken('') }, [network])
 
@@ -89,14 +109,7 @@ export function SendModal({ open, onClose, network, tokens = [], initialToken =
     if (openDropdown) { setOpenDropdown(null) } else { onClose() }
   }
 
-  function toBaseUnits(value: string, decimals: number): string {
-    const [intPart, fracPart = ''] = value.split('.')
-    const frac = fracPart.slice(0, decimals).padEnd(decimals, '0')
-    return (BigInt(intPart || '0') * (10n ** BigInt(decimals)) + BigInt(frac || '0')).toString()
-  }
-
   function handleSubmit() {
-    const isNative = selectedToken === ''
     const convertedAmount = isNative ? toBaseUnits(amount, cfg.nativeDecimals) : amount
     mutation.mutate({
       chain: network,
@@ -258,14 +271,20 @@ export function SendModal({ open, onClose, network, tokens = [], initialToken =
               <button
                 type="button"
                 className={styles.maxBtn}
-                onClick={() => setAmount(walletMatch.bal)}
+                onClick={() => setAmount(maxAmount)}
               >
-                {walletMatch.bal} {tokenLabel}
+                {maxAmount} {tokenLabel}
               </button>
             </div>
           )}
         </div>
 
+        {/* Network fee */}
+        <div className={styles.feeRow}>
+          <span className={styles.feeLabel}>Комиссия сети</span>
+          <span className={styles.feeValue}>≈ {networkFee} {cfg.nativeSymbol}</span>
+        </div>
+
         {/* Error */}
         {mutation.isError && (
           <div className={styles.errorMsg}>