Unified tool replacing manual schema reading (cat schema) across all agents
and skills. Supports 5 commands: init (skeleton), set (incremental field
setting with instant validation), validate (full structural + semantic),
merge (dedup multiple JSONs), info (compact schema summary).
Registers 24 schemas in schema-registry.ts. Updates all agent/skill/command
files to use json_builder info/init/validate instead of cat schema references.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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