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Connection & firewall errors

Refused connections, timeouts, and paths blocked before HTTP.

• CORS policy blocked requestThe browser blocked a cross-origin response because required CORS headers were missing or wrong.
• Docker: no space left on deviceThe daemon or image layers filled the disk—prune images, volumes, or expand the host disk.
• EADDRINUSE — port already in useSomething else is already listening on that TCP port—another dev server or a zombie process.
• ERR_CONNECTION_REFUSEDNothing accepted the TCP connection on that host:port—service down, wrong port, or firewall.
• ETIMEDOUT — connection timed outTCP connection attempts timed out—host unreachable, firewall, or wrong address.
• MongoDB server selection timeoutThe driver could not pick a server in time—replica set issues, DNS, or firewall rules.
• PostgreSQL connection refusedNothing is listening on the Postgres port—service down, wrong port, or Docker networking.
• Redis connection refusedRedis isn’t running or you’re pointing at the wrong host/port in this environment.
• SQLite SQLITE_BUSYConcurrent writers or long transactions held the lock—common in dev with hot reload.
• Stripe invalid API keyThe key is wrong, revoked, or for a different mode (test vs live).
• WebSocket connection failedThe WS handshake did not complete—TLS, proxies, auth headers, or wrong path.