fix: auth, wallet linking, Luca chat, and stablecoin USD pricing

src/lib/truth-engine/providers/alchemy.ts

@@ -1,4 +1,5 @@
 import type { FetchParams, NormalizedTransaction } from "../chain-fetcher";
+import { stablecoinUsd } from "../usd-pricer";
 
 const CHAIN_ENDPOINTS: Record<string, string> = {
   base:      "https://base-mainnet.g.alchemy.com/v2",
@@ -104,6 +105,9 @@ export async function fetchAlchemy(params: FetchParams): Promise<NormalizedTrans
 
       const decStr  = t.rawContract?.decimal;
       const rawVal  = t.rawContract?.value ?? "0x0";
+      const assetAddress = t.rawContract?.address?.toLowerCase() ?? undefined;
+      const decimals = decStr != null ? parseInt(decStr, 10) : undefined;
+      const valueUsd = stablecoinUsd(assetAddress, params.chain, rawVal, decimals);
 
       results.push({
         txHash:       t.hash.toLowerCase(),
@@ -113,14 +117,12 @@ export async function fetchAlchemy(params: FetchParams): Promise<NormalizedTrans
         from:         t.from.toLowerCase(),
         to:           t.to.toLowerCase(),
         assetSymbol:  t.asset ?? "UNKNOWN",
-        assetAddress: t.rawContract?.address?.toLowerCase() ?? undefined,
+        assetAddress,
         rawValue:     rawVal,
-        valueUsd:     undefined,  // Alchemy transfers API does not include USD
+        valueUsd,
         isERC20:      t.category === "erc20",
         chain:        params.chain,
       });
-
-      void decStr; // captured for future USD conversion
     }
   };
 

src/lib/truth-engine/providers/etherscan.ts

@@ -1,4 +1,5 @@
 import type { FetchParams, NormalizedTransaction } from "../chain-fetcher";
+import { stablecoinUsd } from "../usd-pricer";
 
 const CHAIN_APIS: Record<string, string> = {
   base:      "https://api.basescan.org/api",
@@ -88,6 +89,10 @@ export async function fetchEtherscan(params: FetchParams): Promise<NormalizedTra
       if (seen.has(key)) continue;
       seen.add(key);
 
+      const assetAddress = tx.contractAddress?.toLowerCase() ?? undefined;
+      const decimals = tx.tokenDecimal != null ? parseInt(tx.tokenDecimal, 10) : undefined;
+      const valueUsd = stablecoinUsd(assetAddress, params.chain, tx.value, decimals);
+
       results.push({
         txHash:       tx.hash.toLowerCase(),
         blockNumber:  parseInt(tx.blockNumber, 10),
@@ -96,9 +101,9 @@ export async function fetchEtherscan(params: FetchParams): Promise<NormalizedTra
         from:         tx.from.toLowerCase(),
         to:           tx.to.toLowerCase(),
         assetSymbol:  tx.tokenSymbol ?? "ETH",
-        assetAddress: tx.contractAddress?.toLowerCase() ?? undefined,
+        assetAddress,
         rawValue:     tx.value,
-        valueUsd:     undefined,
+        valueUsd,
         isERC20,
         chain:        params.chain,
       });

src/lib/truth-engine/usd-pricer.ts

@@ -0,0 +1,53 @@
+// Deterministic USD pricing for on-chain stablecoin amounts.
+// Stablecoins are pegged 1:1 — USD value = rawValue / 10^decimals.
+// Non-stablecoin assets return undefined (requires a price oracle).
+
+const STABLECOIN_DECIMALS: Record<string, number> = {
+  // Base
+  "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913": 6,   // USDC
+  "0xd9aaec86b65d86f6a7b5b1b0c42ffa531710b6ca": 6,   // USDbC
+  "0x50c5725949a6f0c72e6c4a641f24049a917db0cb": 18,  // DAI
+  // Ethereum
+  "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48": 6,   // USDC
+  "0xdac17f958d2ee523a2206206994597c13d831ec7": 6,   // USDT
+  "0x6b175474e89094c44da98b954eedeac495271d0f": 18,  // DAI
+  // Arbitrum
+  "0xff970a61a04b1ca14834a43f5de4533ebddb5cc8": 6,   // USDC.e
+  "0xaf88d065e77c8cc2239327c5edb3a432268e5831": 6,   // USDC
+  "0xfd086bc7cd5c481dcc9c85ebe478a1c0b69fcbb9": 6,   // USDT
+  // Optimism
+  "0x7f5c764cbc14f9669b88837ca1490cca17c31607": 6,   // USDC.e
+  "0x0b2c639c533813f4aa9d7837caf62653d097ff85": 6,   // USDC
+  "0x94b008aa00579c1307b0ef2c499ab98a8ce58e58": 6,   // USDT
+  // Polygon
+  "0x2791bca1f2de4661ed88a30c99a7a9449aa84174": 6,   // USDC.e
+  "0x3c499c542cef5e3811e1192ce70d8cc03d5c3359": 6,   // USDC
+  "0xc2132d05d31c914a87c6611c10748aeb04b58e8f": 6,   // USDT
+};
+
+export function stablecoinUsd(
+  assetAddress: string | undefined,
+  _chain: string,
+  rawValue: string,
+  decimalsOverride?: number,
+): number | undefined {
+  if (!assetAddress) return undefined;
+  const addr = assetAddress.toLowerCase();
+  const knownDecimals = STABLECOIN_DECIMALS[addr];
+  if (knownDecimals === undefined) return undefined;
+  const decimals = decimalsOverride ?? knownDecimals;
+  if (!rawValue || rawValue === "0x0" || rawValue === "0") return 0;
+  // Parse hex or decimal string as a float via string manipulation to avoid BigInt compat issues
+  let numeric: number;
+  try {
+    if (rawValue.startsWith("0x") || rawValue.startsWith("0X")) {
+      numeric = parseInt(rawValue, 16);
+    } else {
+      numeric = Number(rawValue);
+    }
+  } catch {
+    return undefined;
+  }
+  if (!Number.isFinite(numeric)) return undefined;
+  return numeric / Math.pow(10, decimals);
+}