Send push notifications to users who added your Farcaster Mini App (webhook + notification tokens)

Documented steps

1. Add a webhookUrl property to your /.well-known/farcaster.json manifest so clients can deliver notification tokens.
2. Listen on the webhook: when a user enables notifications, the Farcaster client sends a unique notification token and a send URL to your server.
3. Securely store each token and its send url in a database, keyed to the user's FID.
4. To send: POST to the send url with JSON {notificationId, title, body, targetUrl, tokens:[...]} — batch up to 100 tokens per request.
5. title max 32 chars, body max 128 chars, targetUrl max 1024 chars, notificationId max 128 chars.
6. Parse the response arrays: successfulTokens, invalidTokens (never use again), rateLimitedTokens (retry later).
7. For managed delivery, use Neynar's notification management which handles tokens and targeting without custom webhook code.