[CatOfJupit3r]

Problem

emToZodSchema returns a z.custom schema. Parsing works, but tools that introspect Zod schemas cannot describe it. z.toJSONSchema cannot represent it, so it cannot sit in MCP or model tool input schemas. Consumers who need JSON Schema have to write z.enum(declaration.rawValues), which drops the brand, and then cast back with as unknown as z.ZodType<...>.

Behavior

emToZodSchema(declaration) now returns a native Zod 4 z.enum built from the declaration's .enum member object, typed as the branded member union, with no cast. z.toJSONSchema describes it as { type: "string", enum: [...] }.

Differences from the previous z.custom schema

What the z.custom version did, and what the new one does:

Aspect	z.custom (before)	z.enum (now)
Membership check	declaration.is (string in the member set)	Zod's enum check on the same member set. Members are always strings, so nothing is lost.
Error	custom issue, message Expected one of: A, B	invalid_value issue with values. The message is kept as Expected one of: A, B.
Return type	z.ZodType<Branded>	z.ZodEnum<{ [key]: Branded }>, still assignable to z.ZodType<Branded>. Adds .enum, .options, .extract(), .exclude().
Object declarations (em({ ORDER_PAID: "order-paid" }))	Validated values only	Validates values. The keys stay on schema.enum.
Composed declarations (pick, omit, extend, em.combine, derive-with casing)	Worked through is	Work, because each composed declaration has its own member object (tested for pick and extend).
Transforms or casing at parse time	None	None.
JSON Schema / z.toJSONSchema	Not representable	{ type: "string", enum: [...] }
Zod 3	Supported (^3.25.0 || ^4.0.0)	Not supported. z.enum(object) is Zod 4 API, so the peer range is now ^4.0.0.

Nothing that the z.custom version did needed keeping beyond the error message, which is kept.

Release level

This is a major change for enumwaii, because of the narrower Zod peer range, the different issue code, and the different return type. eslint-plugin-enumwaii gets a patch for the report wording. See the changeset.

Changes

• packages/enumwaii/src/adapters/zod.ts: emToZodSchema returns z.enum(declaration.enum, { error }), with updated JSDoc.
• packages/enumwaii/package.json: zod peer range ^4.0.0.
• Tests: runtime tests (parse, the invalid_value issue and message, options, JSON Schema output, object-declaration keys, pick and extend) and type tests (branded z.output, ZodEnum, composition in z.object, raw literals not assignable).
• Docs: the adapters guide (behavior and a JSON Schema example), the compatibility page, the eslint-plugin docs, and the enumwaii skill.
• prefer-native-schema-adapters: the report says the adapter keeps the branded output type.
• Changeset: enumwaii major, eslint-plugin-enumwaii patch. No version bump or publish in this PR.

Validation

pnpm check passes (exit 0): format, pins, lint, tests (enumwaii 24 passed), type tests, skills, build, API JSDoc, publint/attw, and every example (including the orpc and tanstack-start-solid examples that compose emToZodSchema into z.object).