Add structured error response format across all endpoints

[prodbycorne]

Overview

Error responses are currently unstructured — some endpoints return { error: '...' }, others return HTML Express default errors, and unhandled exceptions leak stack traces. A consistent error format is required for reliable client-side error handling.

Standard Error Response

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Asset code must be 1–12 uppercase alphanumeric characters",
    "details": {
      "field": "assetCode",
      "received": "xlm!!!",
      "constraint": "regex"
    },
    "request_id": "req_01hx3k..."
  }
}

Error Codes

Code	HTTP	Meaning
VALIDATION_ERROR	400	Request schema failure
UNAUTHORIZED	401	Missing or invalid API key
NOT_FOUND	404	Resource does not exist
RATE_LIMITED	429	Too many requests
UPSTREAM_ERROR	502	All price sources failed
INTERNAL_ERROR	500	Unexpected server error

Implementation

1. Create src/errors/AppError.js:

class AppError extends Error {
  constructor(code, message, statusCode, details = {}) { ... }
}

2. Create central error middleware in src/middleware/errorHandler.js:

function errorHandler(err, req, res, next) {
  const isAppError = err instanceof AppError;
  const status = isAppError ? err.statusCode : 500;
  const code = isAppError ? err.code : 'INTERNAL_ERROR';
  const message = isAppError ? err.message : 'An unexpected error occurred';
  // Never leak err.stack to client in production
  res.status(status).json({ error: { code, message, request_id: req.id } });
}

3. Attach request_id (nanoid) to every request via middleware.

Acceptance Criteria

• AppError class created with all codes above
• Central error handler middleware registered last in Express
• Stack traces never sent to clients in production
• request_id on every response (success and error)
• 404 handler for undefined routes
• All existing error throws converted to throw new AppError(...)
• Tests assert error shape for each code

[YfengJ]

Hi maintainers, I would like to apply for this issue if it is still available.

If assigned, I can add a consistent structured error response format across API endpoints, wire existing error paths into it with minimal behavior change, and add focused tests/examples for status, error code, message, and request context fields where available.

I will wait for maintainer or GrantFox assignment/confirmation before cloning, implementing, or opening a PR.