The Generator That Already Existed
The component schema generator in pages-schema had been running for weeks — reading TypeScript interfaces via ts-morph, emitting Zod schemas, catching upstream drift in CI. Issue #420 was about extending the same idea to the four domain YAML formats: CaseDefinition, SWF, HTN, Org.
The hand-written schemas in lsp-schemas were fine as a baseline. But CaseDefinition alone has 826 lines of auto-generated TypeScript types from the YAML schema spec, and those types have [k: string]: unknown index signatures on most sub-objects — a JSON Schema artifact that needs stripping before you can emit useful Zod for LSP completion.
The interesting part was what ts-morph does with these types. CaseDefinition’s Binding type is an intersection: { declared properties } & { [k: string]: unknown }. TypeScript resolves that to an intersection type, not an object type. The generator’s isObject() check missed it entirely — bindings came out as z.unknown(). The fix: add an isIntersection() branch that calls getProperties() on the intersection (which returns the flattened set from all members), then filters out the index signatures.
A second gotcha: getNonNullableType() on unknown returns {} — the empty object type. TypeScript’s type algebra is correct (NonNullable<unknown> IS {}), but a code generator that strips optionality before mapping types silently turns input?: unknown into z.object({}).optional(). The fix was to check for unknown before calling getNonNullableType().
HTN was the recursion test. HtnTaskYaml has methods, each method has tasks, each task can have methods. The generator’s cycle detection via a visited set emits z.lazy(() => htnTaskYamlSchema) at the cycle point — but htnTaskYamlSchema doesn’t exist as a variable. The solution was a lazy reference accumulator: collect cycle-referenced types in a Map during the walk, then emit their z.lazy() declarations as a prelude before the main schema.
All four formats now generate from TypeScript source types, with a staleness test that compares committed schemas against fresh generation. When someone adds a field to CaseHub in the engine repo, CI in blocks-ui fails until the schemas are regenerated. That’s the point — silent drift was the problem this whole issue exists to solve.