Add structured error codes to all server-to-client error frames

[levibliz]

Background

The server currently sends error frames in the format { type: "error", payload: { message: "..." } } but with no machine-readable error code. Clients cannot programmatically distinguish between a validation error, rate limit, authentication failure, or room full condition — they can only parse free-text strings.

Category: Enhancement
Difficulty: Easy
Priority: Medium
Labels: enhancement, backend

Problem Statement

Without error codes, clients must string-match error messages to take action. This is brittle and breaks on any message wording change. A structured code field allows clients to handle errors programmatically.

Requirements

• Add a code field to every error frame sent by the server.
• Define the following error codes as constants in a new src/errors.js module:
  • INVALID_JSON
  • VALIDATION_ERROR
  • RATE_LIMITED
  • ROOM_FULL
  • AUTH_FAILED
• Update all safeSend / error send call-sites in server.js to include the appropriate code.
• Document the error codes in README.md under the Server-to-Client Messages table.

Acceptance Criteria

• All error frames include { type: "error", payload: { message: "...", code: "..." } }.
• src/errors.js exports named constants for all codes.
• README.md documents each error code.
• Existing error-related tests updated to assert code field presence.
• npm run lint exits with code 0.

Files Likely to Change

• src/errors.js (new)
• src/server.js
• README.md
• tests/server.test.js

Definition of Done

Every error frame carries a code field. Clients can switch on code without parsing message strings.

Estimated Complexity

Easy — additive change; no logic modifications required.

[strngecloud]

hi maintainer, i have read the issues description and understand what is expected of me. please assign me this issue i can close it ASAP

[Joyful12-tech]

Hello Maintainer,

I'd like to work on this issue. I'll add structured error codes, update all error responses and documentation, include the required tests, and submit a PR within 2 days.

Thank you!

[almuslavish]

i will like to work on this issue

[grantfox-oss]

🦊 GrantFox — @almuslavish has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #179)
2. Your PR will be reviewed by the RiftCore00 maintainers

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