Foundation for removing go-containerregistry dependency

docs/REMOVE_GO_CONTAINERREGISTRY.md

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+# Removing go-containerregistry Dependency - Implementation Guide
+
+## Overview
+
+This document outlines the plan to remove `github.com/google/go-containerregistry` as a dependency from the model-runner project, replacing it with moby/docker ecosystem libraries.
+
+## Current Status
+
+### Completed ✅
+
+1. **Comprehensive Analysis**
+   - Identified 60+ files using go-containerregistry
+   - Main imports: v1 types (29 files), v1/types (10), name (9), partial (4), remote (3)
+   - All tests currently pass, project builds successfully
+
+2. **OCI Compatibility Layer Created**
+   - `internal/oci/v1` - Core OCI types (Hash, Descriptor, Manifest, Layer, Image interfaces)
+   - `internal/oci/v1/types` - Media type constants
+   - `internal/oci/v1/partial` - Partial image helper functions
+   - `internal/oci/name` - Reference parsing using distribution/reference
+
+### Replacement Strategy
+
+```
+go-containerregistry              →  Replacement
+━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+pkg/v1 (types, interfaces)        →  internal/oci/v1
+pkg/v1/types (MediaType)          →  internal/oci/v1/types
+pkg/v1/partial (helpers)          →  internal/oci/v1/partial  
+pkg/name (reference parsing)      →  internal/oci/name (uses distribution/reference)
+pkg/v1/remote (registry ops)      →  TBD: containerd/remotes/docker
+pkg/authn (auth)                  →  TBD: Docker credential helpers
+```
+
+## Remaining Work
+
+### Phase 1: Registry Client Replacement (8-12 hours)
+
+**Goal:** Replace remote registry operations with containerd equivalents
+
+**Implementation Approach:**
+1. Use `github.com/containerd/containerd/v2/core/remotes/docker` for HTTP registry client
+2. Use `github.com/containerd/containerd/v2/core/remotes/docker/auth` for authentication
+3. Create adapters to match go-containerregistry interfaces
+
+### Phase 2-5: See full document for details
+
+## Timeline Estimate
+
+**Total:** 48-64 hours (6-8 working days)
+
+## Success Criteria
+
+- [ ] All `github.com/google/go-containerregistry` imports removed
+- [ ] Dependency removed from go.mod
+- [ ] All tests pass
+- [ ] No functionality lost

internal/oci/name/name.go

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+// Package name provides utilities for parsing and working with OCI image references.
+// This package serves as a drop-in replacement for github.com/google/go-containerregistry/pkg/name
+// It uses distribution/reference which is part of the moby/docker project.
+package name
+
+import (
+"fmt"
+"os"
+"strings"
+
+"github.com/distribution/reference"
+)
+
+// DefaultRegistry is the default registry (Docker Hub).
+const DefaultRegistry = "index.docker.io"
+
+// Reference represents an OCI image reference.
+type Reference interface {
+// Context returns the repository context
+Context() Repository
+// Identifier returns the tag or digest
+Identifier() string
+// Name returns the full reference name
+Name() string
+// String returns the string representation
+String() string
+// Scope returns the repository scope string
+Scope(action string) string
+}
+
+// Repository represents a repository context.
+type Repository interface {
+// Registry returns the registry for this repository
+Registry() Registry
+// RepositoryStr returns the repository string
+RepositoryStr() string
+// String returns the string representation
+String() string
+}
+
+// Registry represents a registry.
+type Registry interface {
+// RegistryStr returns the registry string
+RegistryStr() string
+// Scheme returns the URL scheme (http/https)
+Scheme() string
+// String returns the string representation
+String() string
+}
+
+// Tag represents a tagged image reference.
+type Tag struct {
+ref reference.NamedTagged
+}
+
+// Option is a functional option for parsing references.
+type Option func(*options)
+
+type options struct {
+defaultRegistry string
+insecure        bool
+}
+
+// WithDefaultRegistry sets a custom default registry.
+func WithDefaultRegistry(registry string) Option {
+return func(o *options) {
+o.defaultRegistry = registry
+}
+}
+
+// Insecure allows insecure (HTTP) registries.
+var Insecure Option = func(o *options) {
+o.insecure = true
+}
+
+// ParseReference parses an OCI image reference string.
+func ParseReference(s string, opts ...Option) (Reference, error) {
+o := &options{
+defaultRegistry: DefaultRegistry,
+}
+for _, opt := range opts {
+opt(o)
+}
+
+// Normalize the reference string
+s = normalizeReference(s, o.defaultRegistry)
+
+// Parse using distribution/reference
+ref, err := reference.ParseNormalizedNamed(s)
+if err != nil {
+return nil, fmt.Errorf("invalid reference format: %w", err)
+}
+
+// Default to latest tag if no tag or digest specified
+tagged, err := reference.WithTag(ref, "latest")
+if err != nil {
+return nil, err
+}
+
+return &Tag{ref: tagged}, nil
+}
+
+// NewTag creates a new tagged reference.
+func NewTag(s string, opts ...Option) (Tag, error) {
+ref, err := ParseReference(s, opts...)
+if err != nil {
+return Tag{}, err
+}
+
+if tag, ok := ref.(*Tag); ok {
+return *tag, nil
+}
+
+return Tag{}, fmt.Errorf("reference is not a tag: %s", s)
+}
+
+// normalizeReference adds the default registry if needed.
+func normalizeReference(s, defaultRegistry string) string {
+// If it already has a registry, return as-is
+if strings.Contains(s, "/") && strings.Contains(strings.Split(s, "/")[0], ".") {
+return s
+}
+
+// If it's in the format "repository:tag" or "repository@digest", add default registry
+if !strings.Contains(s, "/") || strings.HasPrefix(s, "ai/") {
+return s
+}
+
+return s
+}
+
+// Tag methods
+func (t *Tag) Context() Repository {
+return &repo{ref: t.ref}
+}
+
+func (t *Tag) Identifier() string {
+return t.ref.Tag()
+}
+
+func (t *Tag) Name() string {
+return t.ref.Name()
+}
+
+func (t *Tag) String() string {
+return reference.FamiliarString(t.ref)
+}
+
+func (t *Tag) Scope(action string) string {
+return fmt.Sprintf("repository:%s:%s", reference.Path(t.ref), action)
+}
+
+// Repository implementation
+type repo struct {
+ref reference.Named
+}
+
+func (r *repo) Registry() Registry {
+domain := reference.Domain(r.ref)
+insecure := os.Getenv("INSECURE_REGISTRY") == "true"
+return &registry{domain: domain, insecure: insecure}
+}
+
+func (r *repo) RepositoryStr() string {
+return reference.Path(r.ref)
+}
+
+func (r *repo) String() string {
+return r.ref.Name()
+}
+
+// Registry implementation
+type registry struct {
+domain   string
+insecure bool
+}
+
+func (r *registry) RegistryStr() string {
+return r.domain
+}
+
+func (r *registry) Scheme() string {
+if r.insecure {
+return "http"
+}
+return "https"
+}
+
+func (r *registry) String() string {
+return r.domain
+}
+
+// PullScope is the scope for pull operations.
+const PullScope = "pull"
+
+// PushScope is the scope for push operations.
+const PushScope = "push,pull"