Geocoding failures surface a validation error, not silent (0,0) coordinate storage

Silent geocoding failure that stores (0,0) coordinates plants listings in the Gulf of Guinea — visibly off the map for most directories, or worse, clustered with other (0,0) entries in a way that makes them appear at a real but incorrect location. CWE-754 (Improper Check for Unusual Conditions) and CWE-20 (Improper Input Validation) both apply: the application accepts invalid geocoding output without surfacing an error. ISO 25010:2011 reliability is violated because the system produces incorrect outputs without notifying the user. From a business standpoint, silent (0,0) storage corrupts the directory's data integrity and is difficult to detect and backfill at scale.

Reject listing creation when geocoding fails and surface a specific, actionable error message. Do not store a listing with null or (0,0) coordinates.

// src/app/api/listings/route.ts
export async function POST(req: Request) {
  const { address, name } = await req.json();

  const geocoded = await geocodeAddress(address);
  if (!geocoded || geocoded.confidence < 0.8) {
    return Response.json(
      { error: 'Address could not be verified. Please enter a more complete address, including city and postal code.' },
      { status: 400 }
    );
  }

  const listing = await db.listings.create({
    data: { name, address, latitude: geocoded.lat, longitude: geocoded.lng }
  });
  return Response.json(listing);
}

In the submission form, display the API error message directly rather than a generic fallback, so users understand what to correct. Handle all error paths: address not found, API timeout, rate limit exceeded — each should produce a distinct message.