Prompts live in a versioned prompt registry

Prompts are not plain code constants. A prompt registry holds every harness prompt (the system prompt, tool descriptions, the summarizer, evaluators, sub-agent prompts, the prompt-generator catalog) as versioned schemas like modules, easily editable, scoped through the shared scope model, and able to test prompts against each other (variants, experiments, evaluation) wired to the Coral test-drive and evaluation infrastructure. The design choices are UD-P.