fix(middleware): critical Date serialization bug in response sanitization

Problem: All MongoDB Date objects were being serialized as empty {} in API
responses, breaking blog date display across entire site.

Root Cause: removeSensitiveFields() function used spread operator on Date
objects ({...date}), which creates empty object because Dates have no
enumerable properties.

Fix: Added Date instance check before spreading to preserve Date objects
intact for proper JSON.stringify() serialization.

Impact:
- Fixes all blog dates showing 'Invalid Date'
- API now returns proper ISO date strings
- Deployed to production and verified working

Ref: SESSION_HANDOFF_2025-10-23_WEBSITE_AUDIT.md

src/middleware/response-sanitization.middleware.js

@@ -0,0 +1,120 @@
+/**
+ * Response Sanitization Middleware (inst_013, inst_045)
+ * Prevents information disclosure in error responses
+ *
+ * QUICK WIN: Hide stack traces and sensitive data in production
+ * NEVER expose: stack traces, internal paths, environment details
+ */
+
+/**
+ * Sanitize error responses
+ * Production: Generic error messages only
+ * Development: More detailed errors for debugging
+ */
+function sanitizeErrorResponse(err, req, res, next) {
+  const isProduction = process.env.NODE_ENV === 'production';
+
+  // Log full error details internally (always)
+  console.error('[ERROR]', {
+    message: err.message,
+    stack: err.stack,
+    path: req.path,
+    method: req.method,
+    ip: req.ip,
+    user: req.user?.id || req.user?.userId,
+    timestamp: new Date().toISOString()
+  });
+
+  // Determine status code
+  const statusCode = err.statusCode || err.status || 500;
+
+  // Generic error messages for common status codes
+  const genericErrors = {
+    400: 'Bad Request',
+    401: 'Unauthorized',
+    403: 'Forbidden',
+    404: 'Not Found',
+    405: 'Method Not Allowed',
+    413: 'Payload Too Large',
+    429: 'Too Many Requests',
+    500: 'Internal Server Error',
+    502: 'Bad Gateway',
+    503: 'Service Unavailable'
+  };
+
+  // Production: Generic error messages only
+  if (isProduction) {
+    return res.status(statusCode).json({
+      error: genericErrors[statusCode] || 'Error',
+      message: err.message || 'An error occurred',
+      // NEVER include in production: stack, file paths, internal details
+    });
+  }
+
+  // Development: More detailed errors (but still sanitized)
+  res.status(statusCode).json({
+    error: err.name || 'Error',
+    message: err.message,
+    statusCode,
+    // Stack trace only in development
+    stack: process.env.NODE_ENV === 'development' ? err.stack : undefined
+  });
+}
+
+/**
+ * Remove sensitive fields from objects
+ * Useful for sanitizing database results before sending to client
+ */
+function removeSensitiveFields(data, sensitiveFields = ['password', 'passwordHash', 'apiKey', 'secret', 'token']) {
+  if (Array.isArray(data)) {
+    return data.map(item => removeSensitiveFields(item, sensitiveFields));
+  }
+
+  // Preserve Date objects (spreading them creates empty {})
+  if (data instanceof Date) {
+    return data;
+  }
+
+  if (typeof data === 'object' && data !== null) {
+    const sanitized = { ...data };
+
+    // Remove sensitive fields
+    for (const field of sensitiveFields) {
+      delete sanitized[field];
+    }
+
+    // Recursively sanitize nested objects (but skip Dates)
+    for (const key in sanitized) {
+      if (typeof sanitized[key] === 'object' && sanitized[key] !== null) {
+        sanitized[key] = removeSensitiveFields(sanitized[key], sensitiveFields);
+      }
+    }
+
+    return sanitized;
+  }
+
+  return data;
+}
+
+/**
+ * Middleware to sanitize response data
+ * Apply before sending responses with user/database data
+ */
+function sanitizeResponseData(req, res, next) {
+  // Store original json method
+  const originalJson = res.json.bind(res);
+
+  // Override json method to sanitize data
+  res.json = function(data) {
+    const sanitized = removeSensitiveFields(data);
+    return originalJson(sanitized);
+  };
+
+  next();
+}
+
+module.exports = {
+  sanitizeErrorResponse,
+  removeSensitiveFields,
+  sanitizeResponseData
+};