fix(api): stop leaking raw internal errors to callers (#184)

src/api.ts

@@ -32,6 +32,7 @@ import { networkMiddleware, requestNetwork } from "./middleware/network";
 import { renderMetrics, metricsContentType, httpRequestsTotal, httpRequestDurationSeconds } from "./metrics";
 import { getAllCachedTokens, getCachedTokenDecimals } from "./tokenCache";
 import { toDisplayAmount } from "./amount";
+import { HttpError, newCorrelationId } from "./utils/errors";
 
 // ─── RPC Health Check Cache ───────────────────────────────────────────────
 // Keyed by network (#163): one cache entry would let a healthy testnet RPC
@@ -1106,9 +1107,24 @@ export function createApp(): express.Application {
   });
 
   // ─── Global error handler ────────────────────────────────────────────────
-  app.use((err: Error, _req: Request, res: Response, _next: NextFunction) => {
-    console.error("[api] Unhandled error:", err);
-    res.status(500).json({ error: err.message ?? "Internal server error" });
+  app.use((err: unknown, _req: Request, res: Response, _next: NextFunction) => {
+    // A deliberately-thrown HttpError carries a message written for the caller,
+    // so it keeps its own status and text.
+    if (err instanceof HttpError) {
+      return res.status(err.status).json({ error: err.message });
+    }
+
+    // Anything else is unhandled, and its message is not ours to show. This
+    // handler used to answer `err.message` verbatim, which is how a Postgres
+    // connection string reached callers through a raw driver error. The caller
+    // gets a correlation id; the detail stays in the log.
+    const correlationId = newCorrelationId();
+    console.error(`[api] Unhandled error (${correlationId}):`, err);
+
+    return res.status(500).json({
+      error: "Internal server error",
+      correlationId,
+    });
   });
 
   return app;

src/utils/errors.ts

@@ -0,0 +1,13 @@
+import { randomUUID } from 'crypto';
+
+// Errors that are safe to show the caller verbatim (4xx, deliberate)
+export class HttpError extends Error {
+  constructor(public status: number, message: string) {
+    super(message);
+    this.name = 'HttpError';
+  }
+}
+
+export function newCorrelationId(): string {
+  return randomUUID();
+}