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

Introduces a zod package whose only exported mutation, zod.AsSchemas,
rewrites every Interface and Alias in a *guts.Typescript into a
Zod v4 schema VariableStatement plus an inferred type alias. The
mutation also injects `import { z } from "zod"` so the generated file
is self-contained.

Composability is the point. AsSchemas slots into the existing pipeline
alongside the config mutations rather than maintaining a parallel
string-builder. The recommended order is:

    ts.ApplyMutations(
        config.EnumAsTypes,
        config.SimplifyOmitEmpty,
        zod.AsSchemas,
        config.ExportTypes,
    )

EnumAsTypes lowers Go enums to unions of literals; SimplifyOmitEmpty
drops the null half of optional fields; AsSchemas rewrites the
interfaces and aliases; ExportTypes adds `export` to the new
declarations. Other mutations that walk Interface or Alias (ReadOnly,
TrimEnumPrefix, etc.) must run before AsSchemas because the originals
are replaced.

Conversion rules implemented:

- 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([...])`.
- 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 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 are wrapped 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.

Testing:

- testdata/zod/types.go and golden.ts give a realistic end-to-end
  fixture covering structs, embedded fields, enums, nullable pointers,
  arrays, maps, and self-references. testdata/zod/zod.ts is the
  regular guts TS output for the TestGeneration loop.
- zod/zod_test.go pins each conversion case in isolation, including
  the QuestionToken plus nullable interaction, the single-member union
  unwrap, the cross-package prefix passthrough, and the heritage
  extend path.
- zod/zod_e2e_test.go drives the full pipeline against the testdata
  and diffs the output against golden.ts. Run with -update to
  regenerate after intentional changes.

Replaces the string-builder approach in #82 with an AST mutation that
composes with the rest of guts.

Generated by Coder Agents on behalf of @Emyrk.

Author: Emyrk

go.mod

@@ -17,6 +17,7 @@ require (
 	github.com/go-sourcemap/sourcemap v2.1.3+incompatible // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/google/pprof v0.0.0-20230207041349-798e818bf904 // indirect
+	github.com/google/uuid v1.6.0 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/rogpeppe/go-internal v1.14.1 // indirect

go.sum

@@ -15,6 +15,8 @@ github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/google/pprof v0.0.0-20230207041349-798e818bf904 h1:4/hN5RUoecvl+RmJRE2YxKWtnnQls6rQjjW5oV7qg2U=
 github.com/google/pprof v0.0.0-20230207041349-798e818bf904/go.mod h1:uglQLonpP8qtYCYyzA+8c/9qtqgA3qsXGYqCPKARAFg=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=

testdata/zod/golden.ts

@@ -0,0 +1,42 @@
+// Code generated by 'guts'. DO NOT EDIT.
+
+import { z } from "zod";
+
+export type Base = z.infer<typeof BaseSchema>;
+
+export const BaseSchema = z.object({
+    id: z.string(),
+    created_at: z.string(),
+    updated_at: z.string()
+});
+
+export type CreateTicketRequest = z.infer<typeof CreateTicketRequestSchema>;
+
+export const CreateTicketRequestSchema = z.object({
+    title: z.string(),
+    description: z.string().optional(),
+    priority: PrioritySchema,
+    tags: z.array(z.string()).optional()
+});
+
+export type Priority = z.infer<typeof PrioritySchema>;
+
+export const PrioritySchema = z.union([z.literal(2), z.literal(0), z.literal(1)]);
+
+export type Status = z.infer<typeof StatusSchema>;
+
+export const StatusSchema = z.enum(["active", "closed", "pending"]);
+
+export type Ticket = z.infer<typeof TicketSchema>;
+
+export const TicketSchema = BaseSchema.extend({
+    title: z.string(),
+    description: z.string().optional(),
+    status: StatusSchema,
+    priority: PrioritySchema,
+    assignee_id: z.string().optional(),
+    tags: z.array(z.string()),
+    metadata: z.record(z.string(), z.string()).nullable(),
+    children: z.array(z.lazy((): z.ZodType => TicketSchema))
+});
+

testdata/zod/types.go

@@ -0,0 +1,54 @@
+// Package zod provides sample types for testing the Zod mutation.
+package zod
+
+import (
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type Status string
+
+const (
+	StatusActive  Status = "active"
+	StatusPending Status = "pending"
+	StatusClosed  Status = "closed"
+)
+
+type Priority int
+
+const (
+	PriorityLow    Priority = 0
+	PriorityMedium Priority = 1
+	PriorityHigh   Priority = 2
+)
+
+// Base is embedded by Ticket to test heritage/extend.
+type Base struct {
+	ID        uuid.UUID `json:"id"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+}
+
+// Ticket demonstrates a realistic struct with enums, nullable
+// pointers, embedded structs, arrays, and maps.
+type Ticket struct {
+	Base
+
+	Title       string            `json:"title"`
+	Description *string           `json:"description,omitempty"`
+	Status      Status            `json:"status"`
+	Priority    Priority          `json:"priority"`
+	AssigneeID  *uuid.UUID        `json:"assignee_id,omitempty"`
+	Tags        []string          `json:"tags"`
+	Metadata    map[string]string `json:"metadata"`
+	Children    []Ticket          `json:"children"`
+}
+
+// CreateTicketRequest demonstrates a request body type.
+type CreateTicketRequest struct {
+	Title       string   `json:"title"`
+	Description string   `json:"description,omitempty"`
+	Priority    Priority `json:"priority"`
+	Tags        []string `json:"tags,omitempty"`
+}

testdata/zod/zod.ts

@@ -0,0 +1,48 @@
+// Code generated by 'guts'. DO NOT EDIT.
+
+// From zod/types.go
+/**
+ * Base is embedded by Ticket to test heritage/extend.
+ */
+export interface Base {
+    readonly id: string;
+    readonly created_at: string;
+    readonly updated_at: string;
+}
+
+// From zod/types.go
+/**
+ * CreateTicketRequest demonstrates a request body type.
+ */
+export interface CreateTicketRequest {
+    readonly title: string;
+    readonly description?: string;
+    readonly priority: Priority;
+    readonly tags?: readonly string[];
+}
+
+export const Priorities: Priority[] = [2, 0, 1];
+
+// From zod/types.go
+export type Priority = 2 | 0 | 1;
+
+// From zod/types.go
+export type Status = "active" | "closed" | "pending";
+
+export const Statuses: Status[] = ["active", "closed", "pending"];
+
+// From zod/types.go
+/**
+ * Ticket demonstrates a realistic struct with enums, nullable
+ * pointers, embedded structs, arrays, and maps.
+ */
+export interface Ticket extends Base {
+    readonly title: string;
+    readonly description?: string | null;
+    readonly status: Status;
+    readonly priority: Priority;
+    readonly assignee_id?: string | null;
+    readonly tags: readonly string[];
+    readonly metadata: Record<string, string> | null;
+    readonly children: readonly Ticket[];
+}