feat(zod): add AsSchemas mutation for Zod v4 codegen

[Emyrk]

Adds a zod package with one mutation, zod.AsSchemas, that rewrites every Interface and Alias into a Zod v4 schema plus an inferred type alias, and injects import { z } from "zod". Composes with the rest of the config mutations instead of duplicating them as a string-builder.

ts.ApplyMutations(
    config.EnumAsTypes,
    config.SimplifyOmitEmpty,
    zod.AsSchemas,
    config.ExportTypes,
)
out, _ := ts.Serialize()

Replaces the string-builder approach in #82 with an AST mutation. Closes the door on parallel TS output paths: existing mutations like ExportTypes, ReadOnly, TrimEnumPrefix continue to work on the rewritten declarations.

Conversion rules, fixture, test coverage

Pipeline composition

Other mutations that walk Interface or Alias (ReadOnly, TrimEnumPrefix, etc.) must run before AsSchemas because the originals are replaced. ExportTypes runs after because the new VariableStatement and Alias nodes start unmodified; ExportTypes adds export to them.

Conversion rules

• Interface with no heritage: const FooSchema = z.object({...}); plus type Foo = z.infer<typeof FooSchema>;.
• Interface with single-base heritage: BaseSchema.extend({...}) instead of z.object. Multiple bases panic since Zod has no multiple inheritance.
• Alias whose Type is a union of string literals: z.enum([...]) for readability.
• Alias with any other Type: recursive exprToZod plus the inferred type alias.
• Field types: z.string, z.number, z.boolean for keywords; z.array for arrays; z.record(K, V) for Record<K, V>; bare references emit the paired <Name>Schema identifier; T | null collapses to .nullable(); single-non-null-member unions unwrap; QuestionToken appends .optional(); inline TypeLiteralNode emits z.object; intersections fold into a left-associative chain of z.intersection.
• Self-references wrap in z.lazy((): z.ZodType => SelfSchema) so the value-position reference does not fire before the binding exists.
• Cross-package prefix on bindings.Identifier flows through to the emitted schema and reference, matching the rest of the AST. Pinned by TestPrefixedReference.

Mutation API

// zod.AsSchemas
func AsSchemas(ts *guts.Typescript) {
    ts.AppendImport(/* import { z } from "zod" */)
    // walk every Interface and Alias; replace each with a
    // VariableStatement (the schema) plus an Alias (z.infer<>).
}

No options or filter helpers in this PR. If a future use case needs them, a AsSchemasFiltered variant can be added without changing this surface.

Fixture

testdata/zod/types.go defines a Base struct, an embedding Ticket struct with optional pointers, enums, slices, maps, and a self-reference, plus a CreateTicketRequest request body. testdata/zod/golden.ts is the Zod output. testdata/zod/zod.ts is the regular guts TS output, kept so the existing TestGeneration loop also covers this fixture.

Tests

zod/zod_test.go pins each conversion case in isolation. Each test installs a small *guts.Typescript via SetNode, runs AsSchemas, and asserts substrings of the serialized output. Cases:

• TestObjectFields — keyword mappings (z.string, z.number, z.boolean) and QuestionToken.
• TestStringLiteralUnionBecomesEnum — union-of-literals collapses to z.enum, no fallback to z.literal chain.
• TestNullableField — T | null collapses to .nullable().
• TestOptionalNullableField — QuestionToken plus T | null chains to .nullable().optional().
• TestArrayField — z.array(...).
• TestReferenceField — bare reference resolves to <Name>Schema.
• TestRecordField — Record<K, V> to z.record(K, V).
• TestInlineObjectLiteral — inline TypeLiteralNode to z.object.
• TestSelfReferenceLazy — recursive type wraps in z.lazy((): z.ZodType => SelfSchema).
• TestHeritageExtend — single-base heritage to BaseSchema.extend.
• TestAppendsZodImport — pins the import { z } from "zod" injection.
• TestMixedUnionStaysUnion — non-literal, non-T|null union stays as z.union.
• TestSingleMemberUnionUnwraps — single-member union skips z.union wrapper.
• TestPrefixedReference — cross-package Identifier.Prefix reaches both the schema declaration and the reference.

zod/zod_e2e_test.go drives the full pipeline (EnumAsTypes, SimplifyOmitEmpty, AsSchemas, ExportTypes) against testdata/zod/types.go and diffs against testdata/zod/golden.ts. Run with -update to regenerate after intentional changes.

Output style

The TS printer is the source of truth for indentation, quote style, and trailing-comma policy. The PR #82 string-builder produced 2-space indents with trailing commas; this output uses the TS printer's defaults (4-space indents, no trailing commas) because we delegate to ts.createPrinter. If consumers care, they can run Biome or Prettier post-codegen.

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Generated by Coder Agents on behalf of @Emyrk.