fix: Post-purchase holder dashboard on landing page (#150)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/ui-shared/src/composables/useEthPrice.ts

@@ -0,0 +1,65 @@
+import { ref, onMounted, onUnmounted } from 'vue';
+
+const ETH_PRICE_CACHE_MS = 5 * 60 * 1000; // 5 minutes
+
+// Module-level cache shared across all composable instances on the same page
+let _cachedPrice: number | null = null;
+let _cacheTime = 0;
+
+export function formatUsd(usd: number): string {
+  if (usd >= 1000) return `$${(usd / 1000).toFixed(1)}k`;
+  if (usd >= 1) return `$${usd.toFixed(2)}`;
+  if (usd >= 0.01) return `$${usd.toFixed(3)}`;
+  return `$${usd.toFixed(4)}`;
+}
+
+export function formatEthCompact(eth: number): string {
+  if (eth === 0) return '0 ETH';
+  if (eth >= 1) return `${eth.toFixed(2)} ETH`;
+  if (eth >= 0.01) return `${eth.toFixed(4)} ETH`;
+  if (eth >= 0.0001) return `${eth.toFixed(6)} ETH`;
+  return `${eth.toPrecision(4)} ETH`;
+}
+
+export function useEthPrice() {
+  const ethUsdPrice = ref<number | null>(_cachedPrice);
+
+  async function fetchEthPrice() {
+    const now = Date.now();
+    if (_cachedPrice !== null && now - _cacheTime < ETH_PRICE_CACHE_MS) {
+      ethUsdPrice.value = _cachedPrice;
+      return;
+    }
+    try {
+      const controller = new AbortController();
+      const timeout = setTimeout(() => controller.abort(), 5000);
+      const resp = await fetch(
+        'https://api.coingecko.com/api/v3/simple/price?ids=ethereum&vs_currencies=usd',
+        { signal: controller.signal },
+      );
+      clearTimeout(timeout);
+      if (!resp.ok) throw new Error('ETH price fetch failed');
+      const data = await resp.json();
+      if (data.ethereum?.usd) {
+        _cachedPrice = data.ethereum.usd;
+        _cacheTime = now;
+        ethUsdPrice.value = _cachedPrice;
+      }
+    } catch {
+      // Keep existing cached price or null; ETH fallback will be used
+    }
+  }
+
+  let interval: ReturnType<typeof setInterval> | null = null;
+
+  onMounted(async () => {
+    await fetchEthPrice();
+    interval = setInterval(() => void fetchEthPrice(), ETH_PRICE_CACHE_MS);
+  });
+
+  onUnmounted(() => {
+    if (interval) clearInterval(interval);
+  });
+
+  return { ethUsdPrice, fetchEthPrice };
+}

packages/ui-shared/src/composables/useHolderDashboard.ts

@@ -5,8 +5,8 @@ const POLL_INTERVAL_MS = 30_000;
 function formatTokenAmount(rawWei: string, decimals = 18): number {
   try {
     const big = BigInt(rawWei);
-    const divisor = 10 ** decimals;
-    return Number(big) / divisor;
+    // Use BigInt arithmetic to avoid float64 precision loss at high values
+    return Number(big * 10000n / (10n ** BigInt(decimals))) / 10000;
   } catch {
     return 0;
   }