The cycle for each phase
Execute one phase of the plan at a time. This is Spec-Driven Development (SDD): defined scope, validation before moving on.
- Ask the agent to implement the phase (referencing the plan and harness)
- Review the generated code, read it, run locally, test
- Adjust what's needed
- Update the harness if technical decisions were made
- Move on only when the phase works
"Implement phase 1 of the plan: [describe the phase]. Follow the rules in AGENTS.md (or CLAUDE.md if you're using Claude Code). Show me how to test that it's working."
CORS: the problem that will appear
The Deezer API is public and requires no authentication, but does not support CORS. This means fetch() from the browser will be blocked. This will happen.
When the error shows up in the console, don't panic. Ask the agent:
"The fetch to the Deezer API is being blocked by CORS. Set up a CORS proxy (like corsproxy.io) so requests work in the browser. Explain why this happens."
CORS is a browser protection, not a bug in your code. Understanding this is part of the learning.
---Validate functionality
Before moving to deploy, all features need to work locally.
Type "Beyoncé" in your site's search. Artists show up? Click one. Albums load with covers? Click an album. Tracklist appears? If yes, move on.
Chapter 3
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