feat: add modusgraph-gen code generator with private field support and accessor name overrides

[mlwelles]

Summary

Adds modusgraph-gen, a code generation tool that reads Go structs with json/dgraph tags and produces typed CRUD clients, query builders, iterators, and a CLI — with full private field support and customizable accessor names.

Core Generator

Output	Purpose
client_gen.go	Typed Client with per-entity sub-clients
page_options_gen.go	First(n) / Offset(n) pagination helpers
iter_gen.go	Auto-paging SearchIter / ListIter (Go 1.23+ iter.Seq2)
<entity>_gen.go	Per-entity CRUD: Get, Add, Update, Delete, Search, List
<entity>_options_gen.go	Functional options per scalar field
<entity>_query_gen.go	Fluent query builder with filters, ordering, pagination
<entity>_accessors_gen.go	Getters, setters, slice/edge helpers (private fields only)
<entity>_marshal_gen.go	DgraphMap(), UnmarshalJSON(), ValidateWith() (private fields only)
cmd/<pkg>/main.go	Kong CLI with per-entity subcommands and raw DQL query

Private Field Support

Entities with unexported fields get:

• Getters/setters with Go-idiomatic names (name → Name() / SetName())
• Singular edge accessors for *Entity, bare Entity, or validate:"max=1" fields → *Type signatures
• Multi-edge helpers: Append (variadic), Remove (by UID), RemoveFunc (predicate)
• Primitive slice helpers: Append, Remove (by value), RemoveFunc
• DgraphMap() for write-path serialization (bypasses dgman's reflect limitation on unexported fields)
• UnmarshalJSON() for read-path deserialization
• ValidateWith(ctx, validator) for struct validation via a mirror struct with exported fields
• Field opt-out: no json tag → skip; dgraph:"-" → explicit skip

Accessor Name Overrides (New)

Initialism-aware naming: toCamelCase now recognizes the canonical Go lint initialisms (38 entries from golang.org/x/lint). Fields like id produce ID() / SetID() automatically.

Per-field overrides via accessor struct tag:

type Widget struct {
    id   string `json:"id,omitempty" accessor:"ID"`
    url  string `json:"url,omitempty"`           // auto: URL() / SetURL()
    name string `json:"name,omitempty"`           // auto: Name() / SetName()
}

The override applies everywhere: getters, setters, Append*, Remove*, With*Option, UnmarshalJSON alias, ValidateWith mirror, and CLI struct fields.

Engine Changes

• DgraphMapper interface: Insert/Update detect entities with private fields and route through map-based mutation
• InsertRaw for raw struct insertion
• Validator support via WithValidator(...) and SelfValidator interface

Edge Type Coverage

All edge variants are supported and tested:

• []Entity, []*Entity — multi-edge (getter, setter, append, remove, removeFunc)
• *Entity — singular edge (getter, setter)
• Entity (bare value) — singular edge (getter returns *Entity, setter accepts *Entity)
• []Entity / []*Entity + validate:"max=1" or validate:"len=1" — singular edge

Zero New Dependencies

The generator uses only the Go standard library (go/ast, go/parser, text/template, embed).

Usage

//go:generate go run github.com/matthewmcneely/modusgraph/cmd/modusgraph-gen

Testing

• Unit tests: toCamelCase with 33 initialism/compound/edge cases, accessorName with override and fallback, accessor tag parsing
• Golden file tests: all entity types including Studio (private field test fixture with all edge variants)
• Parser tests: parseValidateTag, dgraph:"-", private field detection, singular edge detection, accessor tag
• Generator tests: accessor output, marshal output, CLI output, validator output, edge variants, external imports
• All existing modusGraph tests pass unchanged
• go vet / go build clean

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[mlwelles]

Closing in favor of landing the work directly. This branch was substantially reworked since the PR opened: the private-field serialization approach (and its dgman fork) described in the original PR title was replaced by the public-fielded schema + opt-in generated wrapper layer (see docs/specs/2026-05-18-public-wrapper-types-design.md). The finished work is being merged directly rather than through this stale PR.