feat: add max position limits to TradePanel and page components for enhanced trading controls

src/app/hashtag/[tag]/TradePanel.tsx

@@ -11,11 +11,13 @@ interface Props {
   shortPosition: { shares: number; avgBuyPrice: number } | null
   fundId?: string
   fundName?: string
+  maxPositionShares: number
+  maxPositionValue: number
 }
 
 type Tab = 'BUY_LONG' | 'SELL_LONG' | 'BUY_SHORT' | 'SELL_SHORT'
 
-export function TradePanel({ hashtag, balance, longPosition, shortPosition, fundId, fundName }: Props) {
+export function TradePanel({ hashtag, balance, longPosition, shortPosition, fundId, fundName, maxPositionShares, maxPositionValue }: Props) {
   const router = useRouter()
   const [tab, setTab] = useState<Tab>('BUY_LONG')
   const [shares, setShares] = useState('')
@@ -25,12 +27,19 @@ export function TradePanel({ hashtag, balance, longPosition, shortPosition, fund
   const sharesNum = parseFloat(shares) || 0
   const cost = sharesNum * hashtag.currentPrice
 
-  const maxBuyShares = hashtag.currentPrice > 0 ? Math.floor((balance / hashtag.currentPrice) * 100) / 100 : 0
+  // For buys: max is the lowest of (balance cap, shares cap, value cap) minus existing position
+  const existingBuyShares = tab === 'BUY_LONG' ? (longPosition?.shares ?? 0) : (shortPosition?.shares ?? 0)
+  const remainingShareCap = Math.max(0, maxPositionShares - existingBuyShares)
+  const remainingValueCap = Math.max(0, maxPositionValue - existingBuyShares * hashtag.currentPrice)
+  const sharesFromValueCap = hashtag.currentPrice > 0 ? remainingValueCap / hashtag.currentPrice : 0
+  const sharesFromBalance  = hashtag.currentPrice > 0 ? balance / hashtag.currentPrice : 0
+  const maxBuyShares = Math.floor(Math.min(remainingShareCap, sharesFromValueCap, sharesFromBalance) * 100) / 100
+
   const maxSellShares =
     tab === 'SELL_LONG' ? longPosition?.shares ?? 0 : shortPosition?.shares ?? 0
 
   const canAfford =
-    tab === 'BUY_LONG' || tab === 'BUY_SHORT' ? cost <= balance : sharesNum <= (maxSellShares ?? 0)
+    tab === 'BUY_LONG' || tab === 'BUY_SHORT' ? cost <= balance && sharesNum <= maxBuyShares : sharesNum <= (maxSellShares ?? 0)
 
   async function handleTrade() {
     if (sharesNum <= 0) return
@@ -129,6 +138,9 @@ export function TradePanel({ hashtag, balance, longPosition, shortPosition, fund
             )}
           >
             Max
+            {(tab === 'BUY_LONG' || tab === 'BUY_SHORT') && maxBuyShares === 0
+              ? ' (limit reached)'
+              : null}
           </button>
         </div>
         <input

src/app/hashtag/[tag]/page.tsx

@@ -13,6 +13,10 @@ import { AutoRefresh } from '@/components/AutoRefresh'
 
 const ZOMBIE_ZERO_COUNT = parseInt(process.env.ZOMBIE_ZERO_COUNT ?? '1000', 10)
 const PRICE_UPDATE_INTERVAL_MINUTES = parseInt(process.env.PRICE_UPDATE_INTERVAL_MINUTES ?? '60', 10)
+const MAX_POSITION_SHARES      = parseInt(process.env.MAX_POSITION_SHARES       ?? '100',   10)
+const MAX_POSITION_VALUE       = parseInt(process.env.MAX_POSITION_VALUE        ?? '1000',  10)
+const FUND_MAX_POSITION_SHARES = parseInt(process.env.FUND_MAX_POSITION_SHARES  ?? '1000',  10)
+const FUND_MAX_POSITION_VALUE  = parseInt(process.env.FUND_MAX_POSITION_VALUE   ?? '10000', 10)
 
 export const dynamic = 'force-dynamic'
 
@@ -128,7 +132,7 @@ export default async function HashtagPage({ params, searchParams }: Props) {
   return (
     <div className="space-y-8">
       <AutoRefresh intervalMs={30_000} />
-      {/* Header */}}
+      {/* Header */}
       <div className="flex flex-col sm:flex-row sm:items-end justify-between gap-4">
         <div>
           <h1 className="text-3xl font-bold">#{hashtag.displayTag}</h1>
@@ -193,6 +197,8 @@ export default async function HashtagPage({ params, searchParams }: Props) {
           shortPosition={activeShort ? { shares: activeShort.shares, avgBuyPrice: activeShort.avgBuyPrice } : null}
           fundId={fundContext?.id}
           fundName={fundContext?.name}
+          maxPositionShares={fundContext ? FUND_MAX_POSITION_SHARES : MAX_POSITION_SHARES}
+          maxPositionValue={fundContext ? FUND_MAX_POSITION_VALUE : MAX_POSITION_VALUE}
         />
       ) : (
         <div className="bg-surface-card border border-surface-border rounded-xl p-6 text-center">