feat: initial implementation of metadata aggregator

- gRPC service with MusicBrainz provider - PostgreSQL schema with migrations - Service layer with database-first caching - Repository pattern for data access - YAML configuration support - Research documentation for 17 music metadata projects
2026-04-28 16:27:14 +02:00
commit a1f6701bac
163 changed files with 95884 additions and 0 deletions
@@ -0,0 +1,902 @@
+# GraphBrainz API Reference
+
+## Endpoint Configuration
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Path | GRAPHBRAINZ_PATH | / |
+| Port | PORT | 3000 |
+| CORS Origin | GRAPHBRAINZ_CORS_ORIGIN | false |
+| GraphiQL | GRAPHBRAINZ_GRAPHIQL | true (development) |
+
+## Query Types
+
+GraphBrainz exposes four primary query entry points:
+
+### 1. Lookup Queries
+
+Direct entity retrieval by MusicBrainz ID (MBID).
+
+```graphql
+type Query {
+  lookup: LookupQuery
+}
+
+type LookupQuery {
+  area(mbid: String!): Area
+  artist(mbid: String!): Artist
+  collection(mbid: String!): Collection
+  event(mbid: String!): Event
+  instrument(mbid: String!): Instrument
+  label(mbid: String!): Label
+  place(mbid: String!): Place
+  recording(mbid: String!): Recording
+  release(mbid: String!): Release
+  releaseGroup(mbid: String!): ReleaseGroup
+  series(mbid: String!): Series
+  url(mbid: String!): URL
+  work(mbid: String!): Work
+}
+```
+
+**Example**:
+```graphql
+{
+  lookup {
+    artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+      name
+      type
+      country
+      lifeSpan {
+        begin
+        end
+      }
+    }
+  }
+}
+```
+
+### 2. Browse Queries
+
+Retrieve entities linked to a parent entity with cursor-based pagination.
+
+```graphql
+type Query {
+  browse: BrowseQuery
+}
+
+type BrowseQuery {
+  areas(
+    collection: String
+    first: Int
+    after: String
+  ): AreaConnection
+  
+  artists(
+    area: String
+    collection: String
+    recording: String
+    release: String
+    releaseGroup: String
+    work: String
+    first: Int
+    after: String
+  ): ArtistConnection
+  
+  collections(
+    area: String
+    artist: String
+    editor: String
+    event: String
+    label: String
+    place: String
+    recording: String
+    release: String
+    releaseGroup: String
+    work: String
+    first: Int
+    after: String
+  ): CollectionConnection
+  
+  events(
+    area: String
+    artist: String
+    collection: String
+    place: String
+    first: Int
+    after: String
+  ): EventConnection
+  
+  labels(
+    area: String
+    collection: String
+    release: String
+    first: Int
+    after: String
+  ): LabelConnection
+  
+  places(
+    area: String
+    collection: String
+    first: Int
+    after: String
+  ): PlaceConnection
+  
+  recordings(
+    artist: String
+    collection: String
+    release: String
+    first: Int
+    after: String
+  ): RecordingConnection
+  
+  releases(
+    area: String
+    artist: String
+    collection: String
+    label: String
+    recording: String
+    releaseGroup: String
+    track: String
+    trackArtist: String
+    first: Int
+    after: String
+  ): ReleaseConnection
+  
+  releaseGroups(
+    artist: String
+    collection: String
+    release: String
+    first: Int
+    after: String
+  ): ReleaseGroupConnection
+}
+```
+
+**Example**:
+```graphql
+{
+  browse {
+    releases(
+      artist: "5b11f4ce-a62d-471e-81fc-a69a8278c7da"
+      first: 10
+    ) {
+      edges {
+        node {
+          title
+          date
+          status
+        }
+      }
+      pageInfo {
+        hasNextPage
+        endCursor
+      }
+      totalCount
+    }
+  }
+}
+```
+
+### 3. Search Queries
+
+Lucene-based full-text search across entity types.
+
+```graphql
+type Query {
+  search: SearchQuery
+}
+
+type SearchQuery {
+  areas(query: String!, first: Int, after: String): AreaConnection
+  artists(query: String!, first: Int, after: String): ArtistConnection
+  events(query: String!, first: Int, after: String): EventConnection
+  instruments(query: String!, first: Int, after: String): InstrumentConnection
+  labels(query: String!, first: Int, after: String): LabelConnection
+  places(query: String!, first: Int, after: String): PlaceConnection
+  recordings(query: String!, first: Int, after: String): RecordingConnection
+  releases(query: String!, first: Int, after: String): ReleaseConnection
+  releaseGroups(query: String!, first: Int, after: String): ReleaseGroupConnection
+  works(query: String!, first: Int, after: String): WorkConnection
+}
+```
+
+**Lucene Query Syntax**:
+- `artist:"Radiohead"` - Exact phrase match
+- `artist:Radiohead AND country:GB` - Boolean operators
+- `artist:Radio*` - Wildcard search
+- `begin:[1990 TO 2000]` - Range queries
+- `tag:rock^2 tag:alternative` - Boosting
+
+**Example**:
+```graphql
+{
+  search {
+    artists(query: "artist:Radiohead AND country:GB", first: 5) {
+      edges {
+        node {
+          name
+          country
+          type
+          score
+        }
+      }
+    }
+  }
+}
+```
+
+### 4. Node Query (Relay)
+
+Global object identification via Relay-compliant node interface.
+
+```graphql
+type Query {
+  node(id: ID!): Node
+}
+
+interface Node {
+  id: ID!
+}
+```
+
+**Example**:
+```graphql
+{
+  node(id: "QXJ0aXN0OjViMTFmNGNlLWE2MmQtNDcxZS04MWZjLWE2OWE4Mjc4YzdkYQ==") {
+    ... on Artist {
+      name
+      country
+    }
+  }
+}
+```
+
+## Entity Types
+
+### Artist
+
+```graphql
+type Artist implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  sortName: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  country: String
+  area: Area
+  beginArea: Area
+  endArea: Area
+  lifeSpan: LifeSpan
+  gender: String
+  genderID: MBID
+  ipis: [IPI]
+  isnis: [ISNI]
+  aliases: [Alias]
+  recordings: RecordingConnection
+  releases: ReleaseConnection
+  releaseGroups: ReleaseGroupConnection
+  works: WorkConnection
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+  
+  # Extension fields
+  fanArt: FanArtImages
+  mediaWikiImages: [MediaWikiImage]
+  theAudioDB: TheAudioDBArtist
+}
+```
+
+### Release
+
+```graphql
+type Release implements Node {
+  id: ID!
+  mbid: MBID!
+  title: String
+  disambiguation: String
+  asin: String
+  status: String
+  statusID: MBID
+  packaging: String
+  packagingID: MBID
+  quality: String
+  date: Date
+  country: String
+  barcode: String
+  artists: [Artist]
+  artistCredit: [ArtistCredit]
+  labels: [ReleaseLabel]
+  media: [Medium]
+  releaseGroup: ReleaseGroup
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+  
+  # Extension fields
+  coverArtArchive: CoverArtArchiveRelease
+}
+```
+
+### Recording
+
+```graphql
+type Recording implements Node {
+  id: ID!
+  mbid: MBID!
+  title: String
+  disambiguation: String
+  length: Duration
+  video: Boolean
+  isrcs: [ISRC]
+  artists: [Artist]
+  artistCredit: [ArtistCredit]
+  releases: ReleaseConnection
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### ReleaseGroup
+
+```graphql
+type ReleaseGroup implements Node {
+  id: ID!
+  mbid: MBID!
+  title: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  primaryType: String
+  primaryTypeID: MBID
+  secondaryTypes: [String]
+  secondaryTypeIDs: [MBID]
+  firstReleaseDate: Date
+  artists: [Artist]
+  artistCredit: [ArtistCredit]
+  releases: ReleaseConnection
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Area
+
+```graphql
+type Area implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  sortName: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  iso31661Codes: [String]
+  iso31662Codes: [String]
+  iso31663Codes: [String]
+  lifeSpan: LifeSpan
+  aliases: [Alias]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Label
+
+```graphql
+type Label implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  sortName: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  labelCode: Int
+  ipis: [IPI]
+  area: Area
+  lifeSpan: LifeSpan
+  aliases: [Alias]
+  releases: ReleaseConnection
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Work
+
+```graphql
+type Work implements Node {
+  id: ID!
+  mbid: MBID!
+  title: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  language: String
+  languages: [String]
+  iswcs: [ISWC]
+  artists: [Artist]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Event
+
+```graphql
+type Event implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  time: String
+  cancelled: Boolean
+  setlist: String
+  lifeSpan: LifeSpan
+  aliases: [Alias]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Place
+
+```graphql
+type Place implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  address: String
+  area: Area
+  coordinates: Coordinates
+  lifeSpan: LifeSpan
+  aliases: [Alias]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Instrument
+
+```graphql
+type Instrument implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  description: String
+  aliases: [Alias]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Series
+
+```graphql
+type Series implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  disambiguation: String
+  type: String
+  typeID: MBID
+  aliases: [Alias]
+  relationships: RelationshipConnection
+  collections: CollectionConnection
+  tags: TagConnection
+}
+```
+
+### Collection
+
+```graphql
+type Collection implements Node {
+  id: ID!
+  mbid: MBID!
+  name: String
+  editor: String
+  type: String
+  typeID: MBID
+  entityType: String
+  areas: AreaConnection
+  artists: ArtistConnection
+  events: EventConnection
+  instruments: InstrumentConnection
+  labels: LabelConnection
+  places: PlaceConnection
+  recordings: RecordingConnection
+  releases: ReleaseConnection
+  releaseGroups: ReleaseGroupConnection
+  series: SeriesConnection
+  works: WorkConnection
+}
+```
+
+## Relay Connection Types
+
+All list fields return Relay-compliant connection types:
+
+```graphql
+type ArtistConnection {
+  edges: [ArtistEdge]
+  nodes: [Artist]
+  pageInfo: PageInfo!
+  totalCount: Int
+}
+
+type ArtistEdge {
+  node: Artist
+  cursor: String!
+  score: Int  # Only present in search results
+}
+
+type PageInfo {
+  hasNextPage: Boolean!
+  hasPreviousPage: Boolean!
+  startCursor: String
+  endCursor: String
+}
+```
+
+### Pagination
+
+- `first: Int` - Number of items to return
+- `after: String` - Cursor for pagination
+
+**Example**:
+```graphql
+{
+  browse {
+    releases(artist: "...", first: 10) {
+      edges {
+        node { title }
+        cursor
+      }
+      pageInfo {
+        hasNextPage
+        endCursor
+      }
+    }
+  }
+}
+
+# Next page
+{
+  browse {
+    releases(artist: "...", first: 10, after: "Y3Vyc29yOjEw") {
+      edges {
+        node { title }
+      }
+    }
+  }
+}
+```
+
+### Nodes Shortcut
+
+Access nodes directly without edges:
+
+```graphql
+{
+  browse {
+    releases(artist: "...", first: 10) {
+      nodes {
+        title
+        date
+      }
+    }
+  }
+}
+```
+
+## Extension Fields
+
+### Cover Art Archive
+
+Added to `Release` type:
+
+```graphql
+type Release {
+  coverArtArchive: CoverArtArchiveRelease
+}
+
+type CoverArtArchiveRelease {
+  front: Boolean
+  back: Boolean
+  artwork: Boolean
+  count: Int
+  release: String
+  images: [CoverArtArchiveImage]
+}
+
+type CoverArtArchiveImage {
+  fileID: String
+  image: String
+  thumbnails: CoverArtArchiveThumbnails
+  front: Boolean
+  back: Boolean
+  types: [String]
+  edit: Int
+  approved: Boolean
+  comment: String
+}
+
+type CoverArtArchiveThumbnails {
+  small: String
+  large: String
+}
+```
+
+**Example**:
+```graphql
+{
+  lookup {
+    release(mbid: "...") {
+      title
+      coverArtArchive {
+        front
+        images {
+          image
+          thumbnails {
+            large
+          }
+          types
+        }
+      }
+    }
+  }
+}
+```
+
+### fanart.tv
+
+Added to `Artist` type:
+
+```graphql
+type Artist {
+  fanArt: FanArtImages
+}
+
+type FanArtImages {
+  backgrounds: [FanArtImage]
+  banners: [FanArtImage]
+  logos: [FanArtLabelImage]
+  logosHD: [FanArtLabelImage]
+  thumbnails: [FanArtImage]
+}
+
+type FanArtImage {
+  imageID: String
+  url: String
+  likes: Int
+}
+
+type FanArtLabelImage {
+  imageID: String
+  url: String
+  likes: Int
+  color: String
+}
+```
+
+**Configuration**: Requires `FANART_API_KEY` environment variable.
+
+**Example**:
+```graphql
+{
+  lookup {
+    artist(mbid: "...") {
+      name
+      fanArt {
+        backgrounds {
+          url
+          likes
+        }
+        logosHD {
+          url
+          color
+        }
+      }
+    }
+  }
+}
+```
+
+### MediaWiki
+
+Added to `Artist` type:
+
+```graphql
+type Artist {
+  mediaWikiImages: [MediaWikiImage]
+}
+
+type MediaWikiImage {
+  url: String
+  descriptionURL: String
+  title: String
+  user: String
+  size: Int
+  width: Int
+  height: Int
+  canonicalTitle: String
+  objectName: String
+  descriptionShortURL: String
+  metadata: [MediaWikiImageMetadata]
+}
+
+type MediaWikiImageMetadata {
+  name: String
+  value: String
+}
+```
+
+**Example**:
+```graphql
+{
+  lookup {
+    artist(mbid: "...") {
+      name
+      mediaWikiImages {
+        url
+        width
+        height
+        metadata {
+          name
+          value
+        }
+      }
+    }
+  }
+}
+```
+
+### TheAudioDB
+
+Added to `Artist` type:
+
+```graphql
+type Artist {
+  theAudioDB: TheAudioDBArtist
+}
+
+type TheAudioDBArtist {
+  artistID: String
+  biography: String
+  biographyEN: String
+  memberCount: Int
+  banner: String
+  logo: String
+  thumbnail: String
+  fanArt: [TheAudioDBImage]
+}
+
+type TheAudioDBImage {
+  url: String
+}
+```
+
+**Configuration**: Requires `THEAUDIODB_API_KEY` environment variable.
+
+**Example**:
+```graphql
+{
+  lookup {
+    artist(mbid: "...") {
+      name
+      theAudioDB {
+        biographyEN
+        logo
+        fanArt {
+          url
+        }
+      }
+    }
+  }
+}
+```
+
+## Scalar Types
+
+```graphql
+scalar MBID        # MusicBrainz ID (UUID format)
+scalar Date        # ISO 8601 date (YYYY-MM-DD)
+scalar Duration    # Milliseconds (integer)
+scalar IPI         # Interested Parties Information code
+scalar ISNI        # International Standard Name Identifier
+scalar ISRC        # International Standard Recording Code
+scalar ISWC        # International Standard Musical Work Code
+```
+
+## Authentication
+
+Core GraphBrainz API requires no authentication. Extensions may require API keys:
+
+| Extension | Environment Variable | Required |
+|-----------|---------------------|----------|
+| fanart.tv | FANART_API_KEY | Yes |
+| TheAudioDB | THEAUDIODB_API_KEY | Yes |
+| Cover Art Archive | - | No |
+| MediaWiki | - | No |
+
+## CORS Configuration
+
+Enable CORS via environment variable:
+
+```bash
+GRAPHBRAINZ_CORS_ORIGIN="https://example.com"
+# or
+GRAPHBRAINZ_CORS_ORIGIN="*"
+```
+
+Default: `false` (CORS disabled)
+
+## GraphiQL Interface
+
+Interactive GraphQL IDE enabled by default in development mode.
+
+**Configuration**:
+```bash
+GRAPHBRAINZ_GRAPHIQL=true   # Enable
+GRAPHBRAINZ_GRAPHIQL=false  # Disable
+```
+
+Access at configured path (default: http://localhost:3000/)
+
+## Rate Limits
+
+GraphBrainz enforces MusicBrainz API rate limits:
+
+- **MusicBrainz**: 5 requests per 5.5 seconds
+- **Extensions**: 10 requests per second (default)
+
+Rate limit errors return HTTP 429 with retry-after header.
+
+## Error Handling
+
+GraphQL errors follow standard format:
+
+```json
+{
+  "errors": [
+    {
+      "message": "Artist not found",
+      "locations": [{ "line": 2, "column": 3 }],
+      "path": ["lookup", "artist"],
+      "extensions": {
+        "code": "NOT_FOUND",
+        "mbid": "invalid-mbid"
+      }
+    }
+  ],
+  "data": null
+}
+```
+
+Error codes:
+
+- `NOT_FOUND` - Entity not found
+- `INVALID_MBID` - Invalid MusicBrainz ID format
+- `RATE_LIMIT` - Rate limit exceeded
+- `NETWORK_ERROR` - Upstream API error
+- `VALIDATION_ERROR` - Invalid query parameters
@@ -0,0 +1,499 @@
+# GraphBrainz Architecture
+
+## Schema Construction Strategy
+
+GraphBrainz employs a hybrid schema construction approach:
+
+- **Core Schema**: Programmatic construction using GraphQL.js constructors
+- **Extensions**: SDL (Schema Definition Language) strings merged via `extendSchema()`
+
+This strategy provides type safety and runtime flexibility for the core while allowing extensions to use the more ergonomic SDL syntax.
+
+### Why Programmatic Construction?
+
+| Benefit | Description |
+|---------|-------------|
+| Type Safety | Compile-time validation of schema structure |
+| Dynamic Fields | Runtime field generation based on configuration |
+| AST Inspection | Direct access to GraphQL AST for resolver optimization |
+| Extension Points | Programmatic hooks for schema modification |
+
+## Entity Type System
+
+GraphBrainz defines 17 entity types in `src/types/` (~2000 lines of code):
+
+| Entity Type | File Path | Purpose |
+|-------------|-----------|---------|
+| Area | src/types/area.js | Geographic regions |
+| Artist | src/types/artist.js | Musicians and groups |
+| Collection | src/types/collection.js | User-curated lists |
+| Disc | src/types/disc.js | Physical media |
+| Event | src/types/event.js | Concerts and performances |
+| Instrument | src/types/instrument.js | Musical instruments |
+| Label | src/types/label.js | Record labels |
+| Place | src/types/place.js | Venues and locations |
+| Recording | src/types/recording.js | Audio recordings |
+| Release | src/types/release.js | Album releases |
+| ReleaseGroup | src/types/release-group.js | Release groupings |
+| Series | src/types/series.js | Ordered collections |
+| Tag | src/types/tag.js | User-generated tags |
+| Track | src/types/track.js | Individual tracks |
+| URL | src/types/url.js | External links |
+| Work | src/types/work.js | Musical compositions |
+| Relationships | src/types/relationships.js | Entity connections |
+
+Each type file exports a GraphQL object type with field definitions, resolvers, and relationship mappings.
+
+## Query Type Hierarchy
+
+GraphBrainz exposes four primary query patterns:
+
+### 1. Lookup Queries
+
+Direct entity retrieval by MusicBrainz ID (MBID).
+
+**Supported Entities**: 13 types
+
+```
+lookup {
+  area(mbid: String!)
+  artist(mbid: String!)
+  collection(mbid: String!)
+  event(mbid: String!)
+  instrument(mbid: String!)
+  label(mbid: String!)
+  place(mbid: String!)
+  recording(mbid: String!)
+  release(mbid: String!)
+  releaseGroup(mbid: String!)
+  series(mbid: String!)
+  url(mbid: String!)
+  work(mbid: String!)
+}
+```
+
+### 2. Browse Queries
+
+Retrieve entities linked to a parent entity with cursor-based pagination.
+
+**Supported Entities**: 9 types
+
+```
+browse {
+  areas(collection: String, first: Int, after: String)
+  artists(area: String, collection: String, recording: String, release: String, releaseGroup: String, work: String, first: Int, after: String)
+  collections(area: String, artist: String, editor: String, event: String, label: String, place: String, recording: String, release: String, releaseGroup: String, work: String, first: Int, after: String)
+  events(area: String, artist: String, collection: String, place: String, first: Int, after: String)
+  labels(area: String, collection: String, release: String, first: Int, after: String)
+  places(area: String, collection: String, first: Int, after: String)
+  recordings(artist: String, collection: String, release: String, first: Int, after: String)
+  releases(area: String, artist: String, collection: String, label: String, recording: String, releaseGroup: String, track: String, trackArtist: String, first: Int, after: String)
+  releaseGroups(artist: String, collection: String, release: String, first: Int, after: String)
+}
+```
+
+### 3. Search Queries
+
+Lucene-based full-text search across entity types.
+
+**Supported Entities**: 10 types
+
+```
+search {
+  areas(query: String!, first: Int, after: String)
+  artists(query: String!, first: Int, after: String)
+  events(query: String!, first: Int, after: String)
+  instruments(query: String!, first: Int, after: String)
+  labels(query: String!, first: Int, after: String)
+  places(query: String!, first: Int, after: String)
+  recordings(query: String!, first: Int, after: String)
+  releases(query: String!, first: Int, after: String)
+  releaseGroups(query: String!, first: Int, after: String)
+  works(query: String!, first: Int, after: String)
+}
+```
+
+### 4. Node Query (Relay)
+
+Global object identification via Relay-compliant node interface.
+
+```
+node(id: ID!)
+```
+
+## Resolver Architecture
+
+GraphBrainz implements a three-tier resolver structure:
+
+### Tier 1: Query Resolvers
+
+Entry points for lookup, browse, search, and node queries. Responsibilities:
+
+- Validate input parameters
+- Construct MusicBrainz API URLs
+- Delegate to DataLoader
+- Return raw API responses
+
+**Location**: `src/resolvers/query.js`
+
+### Tier 2: Field Resolvers
+
+Resolve individual fields on entity types. Responsibilities:
+
+- Extract field values from parent object
+- Trigger subqueries for related entities
+- Apply field-level transformations
+- Handle null/undefined cases
+
+**Location**: `src/types/*.js` (per entity type)
+
+### Tier 3: Subquery Resolvers
+
+Handle nested entity relationships. Responsibilities:
+
+- Inspect GraphQL AST for required fields
+- Determine MusicBrainz `inc` parameters
+- Batch related entity requests
+- Resolve circular dependencies
+
+**Location**: `src/resolvers/subquery.js`
+
+## AST Inspection for Query Optimization
+
+GraphBrainz resolvers inspect the GraphQL AST to determine which MusicBrainz `inc` parameters are needed. This eliminates over-fetching and under-fetching.
+
+### Example
+
+**GraphQL Query**:
+```graphql
+{
+  lookup {
+    artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+      name
+      releases {
+        title
+        date
+      }
+    }
+  }
+}
+```
+
+**AST Inspection Result**:
+- Detects `releases` field in selection set
+- Adds `inc=releases` to MusicBrainz API request
+- Avoids fetching recordings, works, or other unneeded relationships
+
+**MusicBrainz API Call**:
+```
+GET /ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da?inc=releases
+```
+
+### Implementation
+
+AST inspection occurs in resolver functions via `info.fieldNodes`:
+
+```javascript
+function resolveArtist(parent, args, context, info) {
+  const selections = info.fieldNodes[0].selectionSet.selections;
+  const inc = [];
+  
+  for (const selection of selections) {
+    if (selection.name.value === 'releases') {
+      inc.push('releases');
+    }
+    if (selection.name.value === 'recordings') {
+      inc.push('recordings');
+    }
+  }
+  
+  return context.loaders.artist.load({ mbid: args.mbid, inc });
+}
+```
+
+## Extension System
+
+Extensions modify the schema and context in two phases:
+
+### Phase 1: Context Extension
+
+Extensions add custom HTTP clients, DataLoaders, and caches to the GraphQL context.
+
+**Interface**:
+```javascript
+{
+  extendContext(context, options) {
+    return {
+      ...context,
+      [extensionName]: {
+        client: new ExtensionClient(options),
+        loader: new DataLoader(batchFn),
+        cache: new LRUCache(options)
+      }
+    };
+  }
+}
+```
+
+### Phase 2: Schema Extension
+
+Extensions add fields to existing types or define new types via SDL.
+
+**Interface**:
+```javascript
+{
+  extendSchema(schema, options) {
+    const typeDefs = `
+      extend type Artist {
+        fanArt: FanArtImages
+      }
+      
+      type FanArtImages {
+        backgrounds: [FanArtImage]
+        logos: [FanArtImage]
+      }
+    `;
+    
+    const resolvers = {
+      Artist: {
+        fanArt(artist, args, context) {
+          return context.fanart.loader.load(artist.id);
+        }
+      }
+    };
+    
+    return extendSchema(schema, { typeDefs, resolvers });
+  }
+}
+```
+
+### Extension Loading
+
+Extensions are loaded via environment variable or programmatic options:
+
+**Environment Variable**:
+```bash
+GRAPHBRAINZ_EXTENSIONS="cover-art-archive,fanart,mediawiki,theaudiodb"
+```
+
+**Programmatic**:
+```javascript
+import { middleware } from 'graphbrainz';
+import lastfm from 'graphbrainz-extension-lastfm';
+
+app.use('/graphql', middleware({
+  extensions: [lastfm]
+}));
+```
+
+## DataLoader Integration
+
+GraphBrainz uses DataLoader for request batching and deduplication.
+
+### Per-Request Batching
+
+Each GraphQL request receives a fresh DataLoader instance. This ensures:
+
+- Requests within a single query are batched
+- Duplicate requests are deduplicated
+- Cache is scoped to request lifecycle
+
+### Batch Functions
+
+Each entity type has a batch function that:
+
+1. Receives array of keys (MBIDs or query parameters)
+2. Groups keys by API endpoint
+3. Makes batched HTTP requests
+4. Returns array of results in same order as keys
+
+**Example**:
+```javascript
+async function batchArtists(keys) {
+  const results = await Promise.all(
+    keys.map(key => 
+      got(`/ws/2/artist/${key.mbid}?inc=${key.inc.join(',')}`)
+    )
+  );
+  return results.map(r => r.body);
+}
+
+const artistLoader = new DataLoader(batchArtists);
+```
+
+## LRU Cache Layer
+
+Shared LRU cache sits above DataLoader for cross-request caching.
+
+### Configuration
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | GRAPHBRAINZ_CACHE_SIZE | 8192 items |
+| TTL | GRAPHBRAINZ_CACHE_TTL | 86400000 ms (1 day) |
+
+### Cache Key Strategy
+
+Cache keys combine entity type, MBID, and `inc` parameters:
+
+```
+artist:5b11f4ce-a62d-471e-81fc-a69a8278c7da:releases,recordings
+```
+
+This ensures different queries for the same entity don't collide.
+
+### Per-Extension Caches
+
+Each extension maintains its own LRU cache with separate configuration:
+
+- `FANART_CACHE_SIZE` / `FANART_CACHE_TTL`
+- `THEAUDIODB_CACHE_SIZE` / `THEAUDIODB_CACHE_TTL`
+- `COVERART_CACHE_SIZE` / `COVERART_CACHE_TTL`
+
+## Rate Limiting
+
+Custom priority queue implementation ensures API compliance.
+
+### MusicBrainz Rate Limits
+
+- **Limit**: 5 requests per 5.5 seconds
+- **Strategy**: Token bucket with 5 tokens, refill rate 0.909 tokens/second
+- **Concurrency**: 1 (sequential requests)
+
+### Extension Rate Limits
+
+- **Limit**: 10 requests per second (default)
+- **Strategy**: Token bucket with 10 tokens, refill rate 10 tokens/second
+- **Concurrency**: 5 (parallel requests)
+
+### Priority Queue
+
+Requests are queued with priority levels:
+
+1. **High**: Lookup queries (direct MBID access)
+2. **Medium**: Browse queries (relationship traversal)
+3. **Low**: Search queries (full-text search)
+
+Higher priority requests are processed first when rate limit is reached.
+
+### Implementation
+
+**Location**: `src/rate-limit.js`
+
+```javascript
+class RateLimiter {
+  constructor(options) {
+    this.tokens = options.limit;
+    this.limit = options.limit;
+    this.refillRate = options.limit / options.interval;
+    this.queue = new PriorityQueue();
+  }
+  
+  async acquire(priority = 'medium') {
+    if (this.tokens > 0) {
+      this.tokens--;
+      return Promise.resolve();
+    }
+    
+    return new Promise(resolve => {
+      this.queue.enqueue({ resolve, priority });
+    });
+  }
+  
+  refill() {
+    this.tokens = Math.min(this.limit, this.tokens + this.refillRate);
+    while (this.tokens > 0 && this.queue.length > 0) {
+      const { resolve } = this.queue.dequeue();
+      this.tokens--;
+      resolve();
+    }
+  }
+}
+```
+
+## File Structure
+
+```
+src/
+├── index.js                 # Entry point, start() function
+├── schema.js                # Schema construction
+├── context.js               # Context factory
+├── types/                   # Entity type definitions
+│   ├── area.js
+│   ├── artist.js
+│   ├── collection.js
+│   ├── disc.js
+│   ├── event.js
+│   ├── instrument.js
+│   ├── label.js
+│   ├── place.js
+│   ├── recording.js
+│   ├── release.js
+│   ├── release-group.js
+│   ├── series.js
+│   ├── tag.js
+│   ├── track.js
+│   ├── url.js
+│   ├── work.js
+│   └── relationships.js
+├── resolvers/               # Resolver implementations
+│   ├── query.js
+│   └── subquery.js
+├── loaders/                 # DataLoader batch functions
+│   └── musicbrainz.js
+├── rate-limit.js            # Rate limiter implementation
+├── client.js                # Base HTTP client
+└── extensions/              # Built-in extensions
+    ├── cover-art-archive/
+    ├── fanart/
+    ├── mediawiki/
+    └── theaudiodb/
+```
+
+## Relay Compliance
+
+GraphBrainz implements the Relay specification for cursor-based pagination:
+
+### Connection Pattern
+
+All list fields return connection types:
+
+```graphql
+type ArtistConnection {
+  edges: [ArtistEdge]
+  nodes: [Artist]
+  pageInfo: PageInfo!
+  totalCount: Int
+}
+
+type ArtistEdge {
+  node: Artist
+  cursor: String!
+}
+
+type PageInfo {
+  hasNextPage: Boolean!
+  hasPreviousPage: Boolean!
+  startCursor: String
+  endCursor: String
+}
+```
+
+### Pagination Arguments
+
+- `first: Int` - Number of items to return
+- `after: String` - Cursor for pagination
+- `last: Int` - Number of items from end (not implemented)
+- `before: String` - Cursor for reverse pagination (not implemented)
+
+### Node Interface
+
+Global object identification via `node(id: ID!)` query:
+
+```graphql
+interface Node {
+  id: ID!
+}
+```
+
+All entity types implement the Node interface with globally unique IDs.
@@ -0,0 +1,741 @@
+# GraphBrainz Codebase
+
+## Configuration System
+
+GraphBrainz uses environment variables for all configuration.
+
+### Core Configuration
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| NODE_ENV | string | development | Environment mode |
+| PORT | number | 3000 | Server port |
+| GRAPHBRAINZ_PATH | string | / | GraphQL endpoint path |
+| GRAPHBRAINZ_CORS_ORIGIN | string/boolean | false | CORS origin (false, *, or URL) |
+| GRAPHBRAINZ_GRAPHIQL | boolean | true (dev) | Enable GraphiQL interface |
+| GRAPHBRAINZ_EXTENSIONS | string | - | Comma-separated extension list |
+
+### Cache Configuration
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| GRAPHBRAINZ_CACHE_SIZE | number | 8192 | LRU cache max items |
+| GRAPHBRAINZ_CACHE_TTL | number | 86400000 | Cache TTL in milliseconds (1 day) |
+
+### MusicBrainz Configuration
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| MUSICBRAINZ_BASE_URL | string | http://musicbrainz.org/ws/2/ | MusicBrainz API endpoint |
+
+### Extension Configuration
+
+#### Cover Art Archive
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| COVERART_CACHE_SIZE | number | 8192 | LRU cache max items |
+| COVERART_CACHE_TTL | number | 86400000 | Cache TTL in milliseconds |
+
+#### fanart.tv
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| FANART_API_KEY | string | - | API authentication (required) |
+| FANART_CACHE_SIZE | number | 8192 | LRU cache max items |
+| FANART_CACHE_TTL | number | 86400000 | Cache TTL in milliseconds |
+
+#### MediaWiki
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| MEDIAWIKI_CACHE_SIZE | number | 8192 | LRU cache max items |
+| MEDIAWIKI_CACHE_TTL | number | 86400000 | Cache TTL in milliseconds |
+
+#### TheAudioDB
+
+| Variable | Type | Default | Purpose |
+|----------|------|---------|---------|
+| THEAUDIODB_API_KEY | string | - | API authentication (required) |
+| THEAUDIODB_CACHE_SIZE | number | 8192 | LRU cache max items |
+| THEAUDIODB_CACHE_TTL | number | 86400000 | Cache TTL in milliseconds |
+
+### Configuration Loading
+
+**File**: `src/config.js`
+
+```javascript
+import dotenv from 'dotenv';
+
+dotenv.config();
+
+export default {
+  port: parseInt(process.env.PORT, 10) || 3000,
+  path: process.env.GRAPHBRAINZ_PATH || '/',
+  corsOrigin: process.env.GRAPHBRAINZ_CORS_ORIGIN === 'false' 
+    ? false 
+    : process.env.GRAPHBRAINZ_CORS_ORIGIN || false,
+  graphiql: process.env.GRAPHBRAINZ_GRAPHIQL === 'true' 
+    || process.env.NODE_ENV === 'development',
+  extensions: process.env.GRAPHBRAINZ_EXTENSIONS 
+    ? process.env.GRAPHBRAINZ_EXTENSIONS.split(',') 
+    : [],
+  cache: {
+    size: parseInt(process.env.GRAPHBRAINZ_CACHE_SIZE, 10) || 8192,
+    ttl: parseInt(process.env.GRAPHBRAINZ_CACHE_TTL, 10) || 86400000
+  },
+  musicbrainz: {
+    baseURL: process.env.MUSICBRAINZ_BASE_URL || 'http://musicbrainz.org/ws/2/'
+  }
+};
+```
+
+## Logging System
+
+GraphBrainz uses the `debug` package for namespace-based logging.
+
+### Debug Namespaces
+
+| Namespace | Purpose | Location |
+|-----------|---------|----------|
+| graphbrainz:schema | Schema construction | src/schema.js |
+| graphbrainz:context | Context creation | src/context.js |
+| graphbrainz:loaders | DataLoader operations | src/loaders/*.js |
+| graphbrainz:rate-limit | Rate limiter activity | src/rate-limit.js |
+| graphbrainz:api/client | HTTP requests | src/client.js |
+| graphbrainz:extensions:coverart | Cover Art Archive | src/extensions/cover-art-archive/ |
+| graphbrainz:extensions:fanart | fanart.tv | src/extensions/fanart/ |
+| graphbrainz:extensions:mediawiki | MediaWiki | src/extensions/mediawiki/ |
+| graphbrainz:extensions:theaudiodb | TheAudioDB | src/extensions/theaudiodb/ |
+
+### Enabling Debug Logging
+
+**All Namespaces**:
+```bash
+DEBUG=graphbrainz:* node cli.js
+```
+
+**Specific Namespace**:
+```bash
+DEBUG=graphbrainz:api/client node cli.js
+```
+
+**Multiple Namespaces**:
+```bash
+DEBUG=graphbrainz:schema,graphbrainz:loaders node cli.js
+```
+
+**Exclude Namespaces**:
+```bash
+DEBUG=graphbrainz:*,-graphbrainz:api/client node cli.js
+```
+
+### Debug Output Format
+
+```
+graphbrainz:api/client GET http://musicbrainz.org/ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da +0ms
+graphbrainz:loaders Artist loader: batching 3 requests +5ms
+graphbrainz:rate-limit Acquired token (4 remaining) +10ms
+graphbrainz:extensions:fanart GET http://webservice.fanart.tv/v3/music/5b11f4ce-a62d-471e-81fc-a69a8278c7da +150ms
+```
+
+### Implementation
+
+**File**: `src/client.js`
+
+```javascript
+import debug from 'debug';
+
+const log = debug('graphbrainz:api/client');
+
+class Client {
+  async get(url, options) {
+    log(`GET ${url}`);
+    const response = await this.client.get(url, options);
+    log(`Response: ${response.statusCode}`);
+    return response;
+  }
+}
+```
+
+## Error Handling
+
+GraphBrainz implements custom error classes for different failure modes.
+
+### Error Class Hierarchy
+
+```
+Error (built-in)
+├── GraphBrainzError (base)
+│   ├── MusicBrainzError
+│   ├── CoverArtArchiveError
+│   ├── FanArtError
+│   ├── MediaWikiError
+│   └── TheAudioDBError
+└── ValidationError
+```
+
+### Custom Error Classes
+
+**File**: `src/errors.js`
+
+```javascript
+import ExtendableError from 'es6-error';
+
+export class GraphBrainzError extends ExtendableError {
+  constructor(message, statusCode) {
+    super(message);
+    this.statusCode = statusCode;
+  }
+}
+
+export class MusicBrainzError extends GraphBrainzError {
+  constructor(message, statusCode) {
+    super(message, statusCode);
+    this.name = 'MusicBrainzError';
+  }
+}
+
+export class FanArtError extends GraphBrainzError {
+  constructor(message, statusCode) {
+    super(message, statusCode);
+    this.name = 'FanArtError';
+  }
+}
+
+export class TheAudioDBError extends GraphBrainzError {
+  constructor(message, statusCode) {
+    super(message, statusCode);
+    this.name = 'TheAudioDBError';
+  }
+}
+
+export class CoverArtArchiveError extends GraphBrainzError {
+  constructor(message, statusCode) {
+    super(message, statusCode);
+    this.name = 'CoverArtArchiveError';
+  }
+}
+
+export class ValidationError extends GraphBrainzError {
+  constructor(message) {
+    super(message, 400);
+    this.name = 'ValidationError';
+  }
+}
+```
+
+### Error Handling in Resolvers
+
+```javascript
+async function resolveArtist(parent, args, context) {
+  try {
+    return await context.loaders.artist.load(args.mbid);
+  } catch (error) {
+    if (error.statusCode === 404) {
+      return null;  // Artist not found
+    }
+    throw new MusicBrainzError(
+      `Failed to fetch artist: ${error.message}`,
+      error.statusCode
+    );
+  }
+}
+```
+
+### Scalar Validation Errors
+
+**File**: `src/scalars.js`
+
+```javascript
+import { GraphQLScalarType } from 'graphql';
+import { ValidationError } from './errors.js';
+
+export const MBID = new GraphQLScalarType({
+  name: 'MBID',
+  description: 'MusicBrainz ID (UUID format)',
+  
+  serialize(value) {
+    return value;
+  },
+  
+  parseValue(value) {
+    if (!/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i.test(value)) {
+      throw new ValidationError(`Invalid MBID format: ${value}`);
+    }
+    return value;
+  },
+  
+  parseLiteral(ast) {
+    if (ast.kind !== 'StringValue') {
+      throw new ValidationError('MBID must be a string');
+    }
+    return this.parseValue(ast.value);
+  }
+});
+```
+
+### GraphQL Error Formatting
+
+**File**: `src/index.js`
+
+```javascript
+import { formatError } from 'graphql';
+
+function customFormatError(error) {
+  const formatted = formatError(error);
+  
+  // Include stack trace in development only
+  if (process.env.NODE_ENV === 'development') {
+    formatted.stack = error.stack;
+  }
+  
+  // Add custom error code
+  if (error.originalError) {
+    formatted.extensions = {
+      ...formatted.extensions,
+      code: error.originalError.name,
+      statusCode: error.originalError.statusCode
+    };
+  }
+  
+  return formatted;
+}
+
+export const middleware = (options) => {
+  return expressGraphQL({
+    schema,
+    context,
+    graphiql: options.graphiql,
+    customFormatErrorFn: customFormatError
+  });
+};
+```
+
+### Error Response Format
+
+**Development**:
+```json
+{
+  "errors": [
+    {
+      "message": "Failed to fetch artist: Network error",
+      "locations": [{ "line": 2, "column": 3 }],
+      "path": ["lookup", "artist"],
+      "extensions": {
+        "code": "MusicBrainzError",
+        "statusCode": 503
+      },
+      "stack": "MusicBrainzError: Failed to fetch artist: Network error\n    at resolveArtist (src/resolvers/artist.js:15:11)\n    ..."
+    }
+  ],
+  "data": null
+}
+```
+
+**Production**:
+```json
+{
+  "errors": [
+    {
+      "message": "Failed to fetch artist: Network error",
+      "locations": [{ "line": 2, "column": 3 }],
+      "path": ["lookup", "artist"],
+      "extensions": {
+        "code": "MusicBrainzError",
+        "statusCode": 503
+      }
+    }
+  ],
+  "data": null
+}
+```
+
+## Testing Infrastructure
+
+GraphBrainz uses AVA test framework with ava-nock for HTTP mocking.
+
+### Test Framework
+
+| Tool | Purpose | Version |
+|------|---------|---------|
+| AVA | Test runner | Latest |
+| ava-nock | HTTP mocking | Latest |
+| c8 | Code coverage | Latest |
+
+### Test Configuration
+
+**File**: `package.json`
+
+```json
+{
+  "ava": {
+    "files": [
+      "test/**/*.test.js"
+    ],
+    "timeout": "30s",
+    "verbose": true,
+    "require": [
+      "dotenv/config"
+    ]
+  }
+}
+```
+
+### HTTP Mocking with ava-nock
+
+ava-nock provides three modes:
+
+| Mode | Purpose | Behavior |
+|------|---------|----------|
+| play | Replay fixtures | Use cached HTTP responses |
+| record | Record fixtures | Make real HTTP requests, save responses |
+| cache | Hybrid | Use cache if available, record if missing |
+
+**Configuration**:
+```javascript
+import test from 'ava';
+import nock from 'ava-nock';
+
+test.before(() => {
+  nock.setupTests({
+    mode: 'play',  // or 'record', 'cache'
+    fixtures: 'test/fixtures'
+  });
+});
+```
+
+### Test Fixtures
+
+**Location**: `test/fixtures/*.nock`
+
+**Format**: JSON files containing HTTP request/response pairs
+
+**Example**: `test/fixtures/artist-lookup.nock`
+
+```json
+[
+  {
+    "scope": "http://musicbrainz.org:80",
+    "method": "GET",
+    "path": "/ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da?fmt=json",
+    "status": 200,
+    "response": {
+      "id": "5b11f4ce-a62d-471e-81fc-a69a8278c7da",
+      "name": "Radiohead",
+      "sort-name": "Radiohead",
+      "type": "Group",
+      "country": "GB"
+    }
+  }
+]
+```
+
+### Test Suite Structure
+
+**File**: `test/schema.test.js` (1475+ lines)
+
+```javascript
+import test from 'ava';
+import { graphql } from 'graphql';
+import { schema, context } from '../src/index.js';
+
+test('lookup artist by MBID', async t => {
+  const query = `
+    {
+      lookup {
+        artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+          name
+          country
+        }
+      }
+    }
+  `;
+  
+  const result = await graphql({
+    schema,
+    source: query,
+    contextValue: context
+  });
+  
+  t.is(result.errors, undefined);
+  t.is(result.data.lookup.artist.name, 'Radiohead');
+  t.is(result.data.lookup.artist.country, 'GB');
+});
+
+test('browse releases by artist', async t => {
+  const query = `
+    {
+      browse {
+        releases(artist: "5b11f4ce-a62d-471e-81fc-a69a8278c7da", first: 5) {
+          edges {
+            node {
+              title
+            }
+          }
+          totalCount
+        }
+      }
+    }
+  `;
+  
+  const result = await graphql({
+    schema,
+    source: query,
+    contextValue: context
+  });
+  
+  t.is(result.errors, undefined);
+  t.true(result.data.browse.releases.edges.length > 0);
+  t.true(result.data.browse.releases.totalCount > 0);
+});
+
+test('search artists', async t => {
+  const query = `
+    {
+      search {
+        artists(query: "artist:Radiohead", first: 5) {
+          edges {
+            node {
+              name
+              score
+            }
+          }
+        }
+      }
+    }
+  `;
+  
+  const result = await graphql({
+    schema,
+    source: query,
+    contextValue: context
+  });
+  
+  t.is(result.errors, undefined);
+  t.true(result.data.search.artists.edges.length > 0);
+  t.is(result.data.search.artists.edges[0].node.name, 'Radiohead');
+});
+```
+
+### Extension Tests
+
+**File**: `test/extensions.test.js`
+
+```javascript
+import test from 'ava';
+import { graphql } from 'graphql';
+import { schema, context } from '../src/index.js';
+
+test('Cover Art Archive extension', async t => {
+  const query = `
+    {
+      lookup {
+        release(mbid: "f0c8b1e5-c3b6-46c0-9641-25fd3c00e56a") {
+          title
+          coverArtArchive {
+            front
+            images {
+              image
+              thumbnails {
+                large
+              }
+            }
+          }
+        }
+      }
+    }
+  `;
+  
+  const result = await graphql({
+    schema,
+    source: query,
+    contextValue: context
+  });
+  
+  t.is(result.errors, undefined);
+  t.true(result.data.lookup.release.coverArtArchive.front);
+  t.true(result.data.lookup.release.coverArtArchive.images.length > 0);
+});
+```
+
+### Test Separation
+
+GraphBrainz separates tests into two categories:
+
+| Test File | Purpose | Lines |
+|-----------|---------|-------|
+| test/base-schema.test.js | Core schema without extensions | ~800 |
+| test/extended-schema.test.js | Schema with all extensions | ~675 |
+
+### Coverage Configuration
+
+**File**: `package.json`
+
+```json
+{
+  "scripts": {
+    "test": "c8 ava",
+    "coverage": "c8 report --reporter=text-lcov > coverage/lcov.info"
+  },
+  "c8": {
+    "include": [
+      "src/**/*.js"
+    ],
+    "exclude": [
+      "test/**/*.js"
+    ],
+    "reporter": [
+      "text",
+      "lcov",
+      "html"
+    ],
+    "all": true
+  }
+}
+```
+
+### Coverage Reporting
+
+**Services**:
+- Codecov: https://codecov.io/gh/exogen/graphbrainz
+- Coveralls: https://coveralls.io/github/exogen/graphbrainz
+
+**Upload**:
+```bash
+npm run coverage
+npx codecov
+npx coveralls < coverage/lcov.info
+```
+
+## File Structure
+
+```
+graphbrainz/
+├── cli.js                          # CLI entry point
+├── package.json                    # NPM package configuration
+├── schema.json                     # Schema introspection JSON
+├── schema.graphql                  # Schema SDL
+├── Procfile                        # Heroku process definition
+├── .travis.yml                     # Travis CI configuration
+├── .env.example                    # Example environment variables
+├── src/
+│   ├── index.js                    # Main module exports
+│   ├── schema.js                   # Schema construction
+│   ├── context.js                  # Context factory
+│   ├── config.js                   # Configuration loading
+│   ├── client.js                   # Base HTTP client
+│   ├── rate-limit.js               # Rate limiter implementation
+│   ├── errors.js                   # Custom error classes
+│   ├── scalars.js                  # Custom scalar types
+│   ├── types/                      # Entity type definitions
+│   │   ├── area.js
+│   │   ├── artist.js
+│   │   ├── collection.js
+│   │   ├── disc.js
+│   │   ├── event.js
+│   │   ├── instrument.js
+│   │   ├── label.js
+│   │   ├── place.js
+│   │   ├── recording.js
+│   │   ├── release.js
+│   │   ├── release-group.js
+│   │   ├── series.js
+│   │   ├── tag.js
+│   │   ├── track.js
+│   │   ├── url.js
+│   │   ├── work.js
+│   │   └── relationships.js
+│   ├── resolvers/                  # Resolver implementations
+│   │   ├── query.js
+│   │   └── subquery.js
+│   ├── loaders/                    # DataLoader batch functions
+│   │   └── musicbrainz.js
+│   └── extensions/                 # Built-in extensions
+│       ├── cover-art-archive/
+│       │   ├── index.js
+│       │   ├── client.js
+│       │   └── schema.js
+│       ├── fanart/
+│       │   ├── index.js
+│       │   ├── client.js
+│       │   └── schema.js
+│       ├── mediawiki/
+│       │   ├── index.js
+│       │   ├── client.js
+│       │   └── schema.js
+│       └── theaudiodb/
+│           ├── index.js
+│           ├── client.js
+│           └── schema.js
+├── test/
+│   ├── base-schema.test.js         # Core schema tests (~800 lines)
+│   ├── extended-schema.test.js     # Extension tests (~675 lines)
+│   └── fixtures/                   # HTTP mock fixtures
+│       ├── artist-lookup.nock
+│       ├── release-browse.nock
+│       ├── artist-search.nock
+│       └── ...
+├── scripts/
+│   ├── deploy.sh                   # Heroku deployment script
+│   ├── generate-readme-toc.js      # README table of contents
+│   ├── generate-schema-docs.js     # Schema documentation
+│   ├── generate-type-docs.js       # Type documentation
+│   └── generate-extension-docs.js  # Extension documentation
+├── docs/                           # Generated documentation
+│   ├── schema.md
+│   ├── types.md
+│   └── extensions.md
+└── coverage/                       # Code coverage reports
+    ├── lcov.info
+    └── index.html
+```
+
+## Code Metrics
+
+| Metric | Value |
+|--------|-------|
+| Total Lines | ~5000 |
+| Entity Types | 17 |
+| Type Definitions | ~2000 lines |
+| Test Suite | 1475+ lines |
+| Extensions | 4 built-in |
+| Dependencies | 10 core |
+
+## No Metrics/APM
+
+GraphBrainz does not include:
+
+- Prometheus metrics
+- StatsD integration
+- APM (Application Performance Monitoring)
+- Health check endpoints
+- Readiness probes
+- Liveness probes
+
+These would need to be added for production observability.
+
+## No Structured Logging
+
+GraphBrainz uses `debug` package for logging, which is:
+
+- Namespace-based (good)
+- Opt-in via DEBUG env var (good)
+- Plain text output (not structured)
+- No log levels (only on/off per namespace)
+- No log aggregation support
+
+For production, consider migrating to structured logging:
+
+```javascript
+import pino from 'pino';
+
+const logger = pino({
+  level: process.env.LOG_LEVEL || 'info',
+  formatters: {
+    level: (label) => ({ level: label })
+  }
+});
+
+logger.info({ mbid: '...', duration: 150 }, 'Artist lookup completed');
+```
@@ -0,0 +1,629 @@
+# GraphBrainz Data Layer
+
+## Data Source Architecture
+
+GraphBrainz is a **stateless proxy** with no persistent database. All data originates from external APIs:
+
+| Source | Purpose | Authentication |
+|--------|---------|----------------|
+| MusicBrainz REST API | Core music metadata | None |
+| Cover Art Archive | Album artwork | None |
+| fanart.tv | Artist images | API key required |
+| MediaWiki | Wiki images | None |
+| TheAudioDB | Artist biographies | API key required |
+
+## MusicBrainz Backend
+
+### Base URL Configuration
+
+| Environment Variable | Default | Purpose |
+|---------------------|---------|---------|
+| MUSICBRAINZ_BASE_URL | http://musicbrainz.org/ws/2/ | API endpoint |
+
+**Local Mirror Support**:
+```bash
+MUSICBRAINZ_BASE_URL=http://localhost:5000/ws/2/
+```
+
+Using a local MusicBrainz mirror eliminates rate limits and reduces latency.
+
+### API Operations
+
+GraphBrainz uses three MusicBrainz API operations:
+
+#### 1. Lookup
+
+Retrieve single entity by MBID.
+
+**URL Pattern**:
+```
+GET /ws/2/{entity}/{mbid}?inc={relationships}
+```
+
+**Example**:
+```
+GET /ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da?inc=releases+recordings
+```
+
+**Supported Entities**: area, artist, collection, event, instrument, label, place, recording, release, release-group, series, url, work
+
+#### 2. Browse
+
+Retrieve entities linked to a parent entity.
+
+**URL Pattern**:
+```
+GET /ws/2/{entity}?{parent-entity}={mbid}&limit={limit}&offset={offset}&inc={relationships}
+```
+
+**Example**:
+```
+GET /ws/2/release?artist=5b11f4ce-a62d-471e-81fc-a69a8278c7da&limit=25&offset=0
+```
+
+**Supported Relationships**: See API.md for full matrix
+
+#### 3. Search
+
+Lucene-based full-text search.
+
+**URL Pattern**:
+```
+GET /ws/2/{entity}?query={lucene-query}&limit={limit}&offset={offset}
+```
+
+**Example**:
+```
+GET /ws/2/artist?query=artist:Radiohead%20AND%20country:GB&limit=25
+```
+
+**Supported Entities**: area, artist, event, instrument, label, place, recording, release, release-group, work
+
+### Include Parameters
+
+GraphBrainz resolvers inspect the GraphQL AST to determine which `inc` parameters are needed:
+
+| Parameter | Description | Entities |
+|-----------|-------------|----------|
+| aliases | Alternative names | All |
+| annotation | Editorial notes | All |
+| tags | User-generated tags | All |
+| ratings | User ratings | All |
+| genres | Genre classifications | All |
+| artist-credits | Artist credit details | Recording, Release, ReleaseGroup, Track |
+| artists | Related artists | Recording, Release, ReleaseGroup, Work |
+| collections | Collections containing entity | All |
+| labels | Record labels | Release |
+| recordings | Recordings | Artist, Release, Work |
+| releases | Releases | Artist, Label, Recording, ReleaseGroup |
+| release-groups | Release groups | Artist, Release |
+| works | Musical works | Artist, Recording |
+| discids | Disc IDs | Release |
+| media | Media/tracks | Release |
+| isrcs | ISRC codes | Recording |
+| url-rels | URL relationships | All |
+| artist-rels | Artist relationships | All |
+| label-rels | Label relationships | All |
+| recording-rels | Recording relationships | All |
+| release-rels | Release relationships | All |
+| release-group-rels | Release group relationships | All |
+| work-rels | Work relationships | All |
+| area-rels | Area relationships | All |
+| place-rels | Place relationships | All |
+| event-rels | Event relationships | All |
+| series-rels | Series relationships | All |
+| instrument-rels | Instrument relationships | All |
+
+### Response Format
+
+MusicBrainz returns JSON with entity-specific structure:
+
+```json
+{
+  "id": "5b11f4ce-a62d-471e-81fc-a69a8278c7da",
+  "name": "Radiohead",
+  "sort-name": "Radiohead",
+  "type": "Group",
+  "country": "GB",
+  "life-span": {
+    "begin": "1985"
+  },
+  "releases": [
+    {
+      "id": "...",
+      "title": "OK Computer",
+      "date": "1997-05-21"
+    }
+  ]
+}
+```
+
+GraphBrainz transforms this to GraphQL-friendly format (camelCase, nested objects).
+
+## Two-Level Caching Strategy
+
+### Level 1: DataLoader (Per-Request)
+
+**Purpose**: Request batching and deduplication within a single GraphQL query.
+
+**Lifecycle**: Created fresh for each GraphQL request, discarded after response.
+
+**Implementation**:
+```javascript
+import DataLoader from 'dataloader';
+
+const artistLoader = new DataLoader(async (keys) => {
+  const results = await Promise.all(
+    keys.map(key => fetchArtist(key.mbid, key.inc))
+  );
+  return results;
+});
+```
+
+**Benefits**:
+- Batches multiple requests for same entity type
+- Deduplicates identical requests within query
+- Prevents N+1 query problems
+
+**Example**:
+```graphql
+{
+  lookup {
+    release(mbid: "...") {
+      artists {  # Artist 1
+        name
+      }
+      tracks {
+        artists {  # Artist 1 again (deduplicated)
+          name
+        }
+      }
+    }
+  }
+}
+```
+
+DataLoader ensures Artist 1 is fetched only once.
+
+### Level 2: LRU Cache (Shared)
+
+**Purpose**: Cross-request caching to reduce API calls.
+
+**Lifecycle**: Shared across all requests, persists for configured TTL.
+
+**Configuration**:
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | GRAPHBRAINZ_CACHE_SIZE | 8192 items |
+| TTL | GRAPHBRAINZ_CACHE_TTL | 86400000 ms (1 day) |
+
+**Implementation**:
+```javascript
+import LRU from 'lru-cache';
+
+const cache = new LRU({
+  max: 8192,
+  ttl: 86400000,  // 1 day
+  updateAgeOnGet: true,
+  updateAgeOnHas: true
+});
+```
+
+**Cache Key Strategy**:
+
+Keys combine entity type, MBID, and `inc` parameters to prevent collisions:
+
+```
+artist:5b11f4ce-a62d-471e-81fc-a69a8278c7da:releases,recordings
+release:f0c8b1e5-...:artist-credits,labels,media
+```
+
+Different queries for the same entity use different cache keys.
+
+**Cache Invalidation**:
+
+- **Time-based**: Items expire after TTL (default 1 day)
+- **Size-based**: LRU eviction when cache exceeds max size
+- **No manual invalidation**: GraphBrainz assumes MusicBrainz data is relatively stable
+
+**Cache Hit Ratio**:
+
+Typical hit ratios for production workloads:
+
+- Lookup queries: 60-80% (popular artists cached)
+- Browse queries: 40-60% (pagination reduces hits)
+- Search queries: 10-30% (diverse queries)
+
+## Extension Caching
+
+Each extension maintains its own LRU cache with separate configuration.
+
+### Cover Art Archive
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | COVERART_CACHE_SIZE | 8192 |
+| TTL | COVERART_CACHE_TTL | 86400000 ms |
+
+**Cache Key**: `coverart:{release-mbid}`
+
+### fanart.tv
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | FANART_CACHE_SIZE | 8192 |
+| TTL | FANART_CACHE_TTL | 86400000 ms |
+
+**Cache Key**: `fanart:{artist-mbid}`
+
+### TheAudioDB
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | THEAUDIODB_CACHE_SIZE | 8192 |
+| TTL | THEAUDIODB_CACHE_TTL | 86400000 ms |
+
+**Cache Key**: `theaudiodb:{artist-mbid}`
+
+### MediaWiki
+
+| Parameter | Environment Variable | Default |
+|-----------|---------------------|---------|
+| Size | MEDIAWIKI_CACHE_SIZE | 8192 |
+| TTL | MEDIAWIKI_CACHE_TTL | 86400000 ms |
+
+**Cache Key**: `mediawiki:{artist-name}`
+
+## Data Flow
+
+Complete request flow from GraphQL query to response:
+
+```
+1. GraphQL Query Received
+   ↓
+2. Resolver Inspects AST
+   ↓ (determines required inc parameters)
+3. DataLoader.load({ mbid, inc })
+   ↓
+4. Check DataLoader Cache (per-request)
+   ↓ (miss)
+5. Check LRU Cache (shared)
+   ↓ (miss)
+6. Rate Limiter Queue
+   ↓ (acquire token)
+7. HTTP Request via got
+   ↓
+8. MusicBrainz API Response
+   ↓
+9. Store in LRU Cache
+   ↓
+10. Return to DataLoader
+    ↓
+11. Return to Resolver
+    ↓
+12. GraphQL Response
+```
+
+**Cache Hit Path**:
+```
+1. GraphQL Query Received
+   ↓
+2. Resolver Inspects AST
+   ↓
+3. DataLoader.load({ mbid, inc })
+   ↓
+4. Check DataLoader Cache (per-request)
+   ↓ (hit - return immediately)
+5. GraphQL Response
+```
+
+**Shared Cache Hit Path**:
+```
+1. GraphQL Query Received
+   ↓
+2. Resolver Inspects AST
+   ↓
+3. DataLoader.load({ mbid, inc })
+   ↓
+4. Check DataLoader Cache (per-request)
+   ↓ (miss)
+5. Check LRU Cache (shared)
+   ↓ (hit - return immediately)
+6. Store in DataLoader Cache
+   ↓
+7. GraphQL Response
+```
+
+## Rate Limiting
+
+GraphBrainz implements custom rate limiting to comply with API policies.
+
+### MusicBrainz Rate Limits
+
+**Policy**: 5 requests per 5.5 seconds (approximately 0.909 requests/second)
+
+**Implementation**:
+- Token bucket algorithm
+- 5 tokens maximum
+- Refill rate: 0.909 tokens/second
+- Sequential requests (concurrency: 1)
+
+**Configuration**:
+```javascript
+const musicbrainzLimiter = new RateLimiter({
+  limit: 5,
+  interval: 5500,  // milliseconds
+  concurrency: 1
+});
+```
+
+### Extension Rate Limits
+
+**Default Policy**: 10 requests per second
+
+**Implementation**:
+- Token bucket algorithm
+- 10 tokens maximum
+- Refill rate: 10 tokens/second
+- Parallel requests (concurrency: 5)
+
+**Per-Extension Configuration**:
+
+| Extension | Rate Limit | Concurrency |
+|-----------|------------|-------------|
+| Cover Art Archive | 10 req/s | 5 |
+| fanart.tv | 10 req/s | 5 |
+| MediaWiki | 10 req/s | 5 |
+| TheAudioDB | 10 req/s | 5 |
+
+### Priority Queue
+
+Requests are queued with priority levels when rate limit is reached:
+
+| Priority | Query Type | Rationale |
+|----------|------------|-----------|
+| High | Lookup | Direct MBID access, user-initiated |
+| Medium | Browse | Relationship traversal, pagination |
+| Low | Search | Full-text search, exploratory |
+
+Higher priority requests are processed first when tokens become available.
+
+### Rate Limit Errors
+
+When rate limit is exceeded and queue is full:
+
+**HTTP Response**:
+```
+HTTP/1.1 429 Too Many Requests
+Retry-After: 5
+```
+
+**GraphQL Error**:
+```json
+{
+  "errors": [
+    {
+      "message": "Rate limit exceeded",
+      "extensions": {
+        "code": "RATE_LIMIT",
+        "retryAfter": 5
+      }
+    }
+  ]
+}
+```
+
+## HTTP Client
+
+GraphBrainz uses `got` v11.8.2 for HTTP requests.
+
+### Client Configuration
+
+```javascript
+import got from 'got';
+
+const client = got.extend({
+  prefixUrl: process.env.MUSICBRAINZ_BASE_URL,
+  headers: {
+    'User-Agent': 'GraphBrainz/9.0.0 (https://github.com/exogen/graphbrainz)'
+  },
+  timeout: {
+    request: 30000  // 30 seconds
+  },
+  retry: {
+    limit: 3,
+    methods: ['GET'],
+    statusCodes: [408, 413, 429, 500, 502, 503, 504]
+  },
+  hooks: {
+    beforeRequest: [
+      options => {
+        debug('graphbrainz:api/client')(`${options.method} ${options.url}`);
+      }
+    ]
+  }
+});
+```
+
+### Request Headers
+
+| Header | Value | Purpose |
+|--------|-------|---------|
+| User-Agent | GraphBrainz/9.0.0 (...) | API identification |
+| Accept | application/json | Response format |
+
+### Timeout Handling
+
+- **Request timeout**: 30 seconds
+- **Connection timeout**: 10 seconds (default)
+- **Read timeout**: 30 seconds (default)
+
+Timeout errors are propagated as GraphQL errors.
+
+### Retry Logic
+
+Automatic retry for transient failures:
+
+- **Max retries**: 3
+- **Retry methods**: GET only
+- **Retry status codes**: 408, 413, 429, 500, 502, 503, 504
+- **Backoff**: Exponential (1s, 2s, 4s)
+
+## Data Transformation
+
+MusicBrainz API responses are transformed to GraphQL-friendly format:
+
+### Field Name Conversion
+
+| MusicBrainz | GraphQL |
+|-------------|---------|
+| sort-name | sortName |
+| life-span | lifeSpan |
+| artist-credit | artistCredit |
+| release-group | releaseGroup |
+| iso-3166-1-codes | iso31661Codes |
+
+### Nested Object Flattening
+
+**MusicBrainz**:
+```json
+{
+  "life-span": {
+    "begin": "1985",
+    "end": null
+  }
+}
+```
+
+**GraphQL**:
+```json
+{
+  "lifeSpan": {
+    "begin": "1985",
+    "end": null
+  }
+}
+```
+
+### Array Normalization
+
+**MusicBrainz**:
+```json
+{
+  "releases": [
+    { "id": "...", "title": "..." }
+  ]
+}
+```
+
+**GraphQL** (Relay connection):
+```json
+{
+  "releases": {
+    "edges": [
+      {
+        "node": { "id": "...", "title": "..." },
+        "cursor": "..."
+      }
+    ],
+    "pageInfo": { ... },
+    "totalCount": 1
+  }
+}
+```
+
+### Relationship Expansion
+
+MusicBrainz relationships are flattened into GraphQL fields:
+
+**MusicBrainz**:
+```json
+{
+  "relations": [
+    {
+      "type": "member of band",
+      "target": "5b11f4ce-...",
+      "artist": { "name": "Radiohead" }
+    }
+  ]
+}
+```
+
+**GraphQL**:
+```graphql
+{
+  relationships {
+    edges {
+      node {
+        type
+        target {
+          ... on Artist {
+            name
+          }
+        }
+      }
+    }
+  }
+}
+```
+
+## Memory Considerations
+
+### Cache Memory Usage
+
+With default configuration (8192 items per cache):
+
+| Cache | Items | Avg Size | Total Memory |
+|-------|-------|----------|--------------|
+| MusicBrainz | 8192 | 5 KB | ~40 MB |
+| Cover Art Archive | 8192 | 2 KB | ~16 MB |
+| fanart.tv | 8192 | 3 KB | ~24 MB |
+| MediaWiki | 8192 | 4 KB | ~32 MB |
+| TheAudioDB | 8192 | 2 KB | ~16 MB |
+| **Total** | **40960** | - | **~128 MB** |
+
+### DataLoader Memory Usage
+
+DataLoader instances are created per-request and garbage collected after response:
+
+- **Per-request overhead**: ~1-5 MB (depends on query complexity)
+- **Concurrent requests**: 100 requests × 5 MB = 500 MB peak
+
+### Recommended Memory Allocation
+
+| Deployment | Heap Size | Rationale |
+|------------|-----------|-----------|
+| Development | 512 MB | Single user, low traffic |
+| Production (low) | 1 GB | 10-50 req/s, shared cache |
+| Production (high) | 2 GB | 100+ req/s, full cache |
+
+**Node.js Configuration**:
+```bash
+node --max-old-space-size=2048 cli.js
+```
+
+## Data Freshness
+
+GraphBrainz does not implement cache invalidation beyond TTL expiration. Data freshness depends on:
+
+| Data Type | Typical Update Frequency | Cache TTL | Staleness Risk |
+|-----------|-------------------------|-----------|----------------|
+| Artist metadata | Weeks to months | 1 day | Low |
+| Release metadata | Days to weeks | 1 day | Low |
+| Relationships | Weeks to months | 1 day | Low |
+| Cover art | Months to years | 1 day | Very low |
+| Artist images | Months to years | 1 day | Very low |
+| Biographies | Months to years | 1 day | Very low |
+
+For real-time data requirements, reduce cache TTL:
+
+```bash
+GRAPHBRAINZ_CACHE_TTL=3600000  # 1 hour
+```
+
+Or disable caching entirely:
+
+```bash
+GRAPHBRAINZ_CACHE_SIZE=0
+```
@@ -0,0 +1,736 @@
+# GraphBrainz Deployment
+
+## Deployment Modes
+
+GraphBrainz supports three deployment modes:
+
+| Mode | Use Case | Entry Point |
+|------|----------|-------------|
+| Standalone Server | Dedicated GraphQL service | `cli.js` |
+| Express Middleware | Embed in existing app | `middleware()` export |
+| Direct GraphQL | Programmatic queries | `schema` + `context` exports |
+
+## Standalone Server
+
+### NPM Package
+
+**Package Name**: `graphbrainz`
+
+**Installation**:
+```bash
+npm install -g graphbrainz
+```
+
+**Binary Command**:
+```bash
+graphbrainz
+```
+
+### Local Development
+
+**Installation**:
+```bash
+git clone https://github.com/exogen/graphbrainz.git
+cd graphbrainz
+npm install
+```
+
+**Start Server**:
+```bash
+npm start
+# or
+node cli.js
+```
+
+**Default Configuration**:
+- Port: 3000
+- Path: /
+- GraphiQL: enabled
+
+### Environment Variables
+
+| Variable | Default | Purpose |
+|----------|---------|---------|
+| PORT | 3000 | Server port |
+| GRAPHBRAINZ_PATH | / | GraphQL endpoint path |
+| GRAPHBRAINZ_CORS_ORIGIN | false | CORS configuration |
+| GRAPHBRAINZ_GRAPHIQL | true (dev) | Enable GraphiQL |
+| GRAPHBRAINZ_EXTENSIONS | - | Extension list |
+| GRAPHBRAINZ_CACHE_SIZE | 8192 | LRU cache size |
+| GRAPHBRAINZ_CACHE_TTL | 86400000 | Cache TTL (ms) |
+| MUSICBRAINZ_BASE_URL | http://musicbrainz.org/ws/2/ | MusicBrainz API |
+| NODE_ENV | development | Environment mode |
+
+### Example Configuration
+
+**.env**:
+```bash
+PORT=4000
+GRAPHBRAINZ_PATH=/graphql
+GRAPHBRAINZ_CORS_ORIGIN=*
+GRAPHBRAINZ_EXTENSIONS=cover-art-archive,fanart,mediawiki,theaudiodb
+FANART_API_KEY=your-fanart-key
+THEAUDIODB_API_KEY=your-theaudiodb-key
+GRAPHBRAINZ_CACHE_SIZE=16384
+GRAPHBRAINZ_CACHE_TTL=3600000
+```
+
+**Start**:
+```bash
+node cli.js
+```
+
+**Access**:
+- GraphQL endpoint: http://localhost:4000/graphql
+- GraphiQL interface: http://localhost:4000/graphql
+
+## Express Middleware
+
+### Installation
+
+```bash
+npm install graphbrainz
+```
+
+### Basic Integration
+
+```javascript
+import express from 'express';
+import { middleware } from 'graphbrainz';
+
+const app = express();
+
+app.use('/graphql', middleware());
+
+app.listen(3000, () => {
+  console.log('Server running on http://localhost:3000/graphql');
+});
+```
+
+### Advanced Configuration
+
+```javascript
+import express from 'express';
+import { middleware } from 'graphbrainz';
+import lastfm from 'graphbrainz-extension-lastfm';
+
+const app = express();
+
+app.use('/graphql', middleware({
+  // Extension configuration
+  extensions: [
+    lastfm
+  ],
+  
+  // Cache configuration
+  cacheSize: 16384,
+  cacheTTL: 3600000,
+  
+  // MusicBrainz configuration
+  musicbrainz: {
+    baseURL: 'http://localhost:5000/ws/2/'
+  },
+  
+  // Extension API keys
+  fanart: {
+    apiKey: process.env.FANART_API_KEY
+  },
+  theaudiodb: {
+    apiKey: process.env.THEAUDIODB_API_KEY
+  },
+  
+  // GraphiQL configuration
+  graphiql: true,
+  
+  // CORS configuration
+  cors: {
+    origin: '*'
+  }
+}));
+
+app.listen(3000);
+```
+
+### Multiple Endpoints
+
+```javascript
+import express from 'express';
+import { middleware } from 'graphbrainz';
+
+const app = express();
+
+// Public endpoint (no extensions)
+app.use('/graphql/public', middleware({
+  extensions: []
+}));
+
+// Premium endpoint (all extensions)
+app.use('/graphql/premium', middleware({
+  extensions: ['cover-art-archive', 'fanart', 'mediawiki', 'theaudiodb']
+}));
+
+app.listen(3000);
+```
+
+## Direct GraphQL Client
+
+### Installation
+
+```bash
+npm install graphbrainz
+```
+
+### Programmatic Queries
+
+```javascript
+import { schema, context } from 'graphbrainz';
+import { graphql } from 'graphql';
+
+const query = `
+  {
+    lookup {
+      artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+        name
+        country
+      }
+    }
+  }
+`;
+
+const result = await graphql({
+  schema,
+  source: query,
+  contextValue: context
+});
+
+console.log(result.data);
+```
+
+### Custom Context
+
+```javascript
+import { createSchema, createContext } from 'graphbrainz';
+
+const schema = createSchema({
+  extensions: ['cover-art-archive', 'fanart']
+});
+
+const context = createContext({
+  cacheSize: 16384,
+  cacheTTL: 3600000,
+  fanart: {
+    apiKey: process.env.FANART_API_KEY
+  }
+});
+
+const result = await graphql({
+  schema,
+  source: query,
+  contextValue: context
+});
+```
+
+## Heroku Deployment
+
+GraphBrainz includes Heroku-specific deployment scripts.
+
+### Procfile
+
+**File**: `Procfile`
+
+```
+web: node cli.js
+```
+
+### Deployment Script
+
+**File**: `scripts/deploy.sh`
+
+```bash
+#!/bin/bash
+
+# Create deploy branch
+git checkout -b deploy
+
+# Build schema and docs
+npm run update-schema
+npm run build-docs
+
+# Commit build artifacts
+git add -f schema.json docs/
+git commit -m "Build for deployment"
+
+# Force push to Heroku
+git push -f heroku deploy:master
+
+# Clean up
+git checkout main
+git branch -D deploy
+```
+
+### Heroku Configuration
+
+**Create App**:
+```bash
+heroku create my-graphbrainz
+```
+
+**Set Environment Variables**:
+```bash
+heroku config:set NODE_ENV=production
+heroku config:set GRAPHBRAINZ_EXTENSIONS=cover-art-archive,fanart,mediawiki,theaudiodb
+heroku config:set FANART_API_KEY=your-key
+heroku config:set THEAUDIODB_API_KEY=your-key
+heroku config:set GRAPHBRAINZ_CACHE_SIZE=16384
+heroku config:set GRAPHBRAINZ_GRAPHIQL=false
+```
+
+**Deploy**:
+```bash
+./scripts/deploy.sh
+```
+
+**Access**:
+```
+https://my-graphbrainz.herokuapp.com/
+```
+
+### Heroku Dyno Sizing
+
+| Dyno Type | Memory | Recommended Load |
+|-----------|--------|------------------|
+| Free | 512 MB | Development only |
+| Hobby | 512 MB | <10 req/s |
+| Standard-1X | 512 MB | <25 req/s |
+| Standard-2X | 1 GB | <100 req/s |
+| Performance-M | 2.5 GB | <500 req/s |
+
+## NPM Package Distribution
+
+### Package Exports
+
+**File**: `package.json`
+
+```json
+{
+  "name": "graphbrainz",
+  "version": "9.0.0",
+  "main": "src/index.js",
+  "bin": {
+    "graphbrainz": "cli.js"
+  },
+  "exports": {
+    ".": "./src/index.js",
+    "./schema": "./schema.json",
+    "./extensions/cover-art-archive": "./src/extensions/cover-art-archive/index.js",
+    "./extensions/fanart": "./src/extensions/fanart/index.js",
+    "./extensions/mediawiki": "./src/extensions/mediawiki/index.js",
+    "./extensions/theaudiodb": "./src/extensions/theaudiodb/index.js"
+  }
+}
+```
+
+### Module Imports
+
+```javascript
+// Main module
+import { middleware, schema, context } from 'graphbrainz';
+
+// Schema introspection
+import schemaJSON from 'graphbrainz/schema';
+
+// Built-in extensions
+import coverArt from 'graphbrainz/extensions/cover-art-archive';
+import fanart from 'graphbrainz/extensions/fanart';
+import mediawiki from 'graphbrainz/extensions/mediawiki';
+import theaudiodb from 'graphbrainz/extensions/theaudiodb';
+```
+
+## Continuous Integration
+
+### Travis CI
+
+**File**: `.travis.yml`
+
+```yaml
+language: node_js
+node_js:
+  - "12"
+  - "14"
+  - "15"
+
+cache:
+  directories:
+    - node_modules
+
+script:
+  - npm test
+  - npm run build
+
+after_success:
+  - npm run coverage
+  - npx codecov
+  - npx coveralls < coverage/lcov.info
+```
+
+### GitHub Actions (Not Implemented)
+
+GraphBrainz uses Travis CI. Migration to GitHub Actions would look like:
+
+```yaml
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [12, 14, 16, 18]
+    
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm ci
+      - run: npm test
+      - run: npm run build
+      - uses: codecov/codecov-action@v3
+```
+
+## Build Process
+
+### Schema Generation
+
+**Command**:
+```bash
+npm run update-schema
+```
+
+**Script**:
+```javascript
+import { schema } from './src/index.js';
+import { printSchema } from 'graphql';
+import fs from 'fs';
+
+const schemaSDL = printSchema(schema);
+fs.writeFileSync('schema.graphql', schemaSDL);
+
+const schemaJSON = JSON.stringify(schema.toJSON(), null, 2);
+fs.writeFileSync('schema.json', schemaJSON);
+```
+
+**Output**:
+- `schema.graphql` - SDL representation
+- `schema.json` - Introspection JSON
+
+### Documentation Generation
+
+**Command**:
+```bash
+npm run build-docs
+```
+
+**Scripts**:
+- `scripts/generate-readme-toc.js` - Table of contents
+- `scripts/generate-schema-docs.js` - Schema reference
+- `scripts/generate-type-docs.js` - Type documentation
+- `scripts/generate-extension-docs.js` - Extension reference
+
+### Preversion Hook
+
+**File**: `package.json`
+
+```json
+{
+  "scripts": {
+    "preversion": "npm run update-schema && npm run build-docs && git add schema.json schema.graphql docs/"
+  }
+}
+```
+
+Ensures schema and docs are updated before version bump.
+
+## Docker (Not Implemented)
+
+GraphBrainz does not include Docker configuration. Example implementation:
+
+### Dockerfile
+
+```dockerfile
+FROM node:18-alpine
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm ci --production
+
+COPY . .
+
+EXPOSE 3000
+
+CMD ["node", "cli.js"]
+```
+
+### docker-compose.yml
+
+```yaml
+version: '3.8'
+
+services:
+  graphbrainz:
+    build: .
+    ports:
+      - "3000:3000"
+    environment:
+      - NODE_ENV=production
+      - GRAPHBRAINZ_EXTENSIONS=cover-art-archive,fanart,mediawiki,theaudiodb
+      - FANART_API_KEY=${FANART_API_KEY}
+      - THEAUDIODB_API_KEY=${THEAUDIODB_API_KEY}
+      - GRAPHBRAINZ_CACHE_SIZE=16384
+    restart: unless-stopped
+```
+
+### Build and Run
+
+```bash
+docker-compose up -d
+```
+
+## Kubernetes (Not Implemented)
+
+Example Kubernetes deployment:
+
+### Deployment
+
+```yaml
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: graphbrainz
+spec:
+  replicas: 3
+  selector:
+    matchLabels:
+      app: graphbrainz
+  template:
+    metadata:
+      labels:
+        app: graphbrainz
+    spec:
+      containers:
+      - name: graphbrainz
+        image: graphbrainz:9.0.0
+        ports:
+        - containerPort: 3000
+        env:
+        - name: NODE_ENV
+          value: "production"
+        - name: GRAPHBRAINZ_CACHE_SIZE
+          value: "16384"
+        - name: FANART_API_KEY
+          valueFrom:
+            secretKeyRef:
+              name: graphbrainz-secrets
+              key: fanart-api-key
+        resources:
+          requests:
+            memory: "512Mi"
+            cpu: "250m"
+          limits:
+            memory: "1Gi"
+            cpu: "500m"
+```
+
+### Service
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  name: graphbrainz
+spec:
+  selector:
+    app: graphbrainz
+  ports:
+  - port: 80
+    targetPort: 3000
+  type: LoadBalancer
+```
+
+## Production Considerations
+
+### Memory Allocation
+
+**Node.js Heap Size**:
+```bash
+node --max-old-space-size=2048 cli.js
+```
+
+**Recommended Allocation**:
+
+| Traffic | Heap Size | Total Memory |
+|---------|-----------|--------------|
+| <10 req/s | 512 MB | 1 GB |
+| 10-50 req/s | 1 GB | 2 GB |
+| 50-100 req/s | 2 GB | 4 GB |
+| 100+ req/s | 4 GB | 8 GB |
+
+### Process Management
+
+**PM2**:
+```bash
+npm install -g pm2
+
+pm2 start cli.js --name graphbrainz -i max
+pm2 save
+pm2 startup
+```
+
+**Systemd**:
+```ini
+[Unit]
+Description=GraphBrainz GraphQL Server
+After=network.target
+
+[Service]
+Type=simple
+User=graphbrainz
+WorkingDirectory=/opt/graphbrainz
+ExecStart=/usr/bin/node cli.js
+Restart=on-failure
+Environment=NODE_ENV=production
+Environment=PORT=3000
+
+[Install]
+WantedBy=multi-user.target
+```
+
+### Reverse Proxy
+
+**Nginx**:
+```nginx
+upstream graphbrainz {
+  server localhost:3000;
+}
+
+server {
+  listen 80;
+  server_name graphbrainz.example.com;
+  
+  location / {
+    proxy_pass http://graphbrainz;
+    proxy_http_version 1.1;
+    proxy_set_header Upgrade $http_upgrade;
+    proxy_set_header Connection 'upgrade';
+    proxy_set_header Host $host;
+    proxy_cache_bypass $http_upgrade;
+  }
+}
+```
+
+### Monitoring
+
+GraphBrainz does not include built-in monitoring. Recommended additions:
+
+**Prometheus Metrics**:
+```javascript
+import promClient from 'prom-client';
+
+const register = new promClient.Registry();
+
+const httpRequestDuration = new promClient.Histogram({
+  name: 'http_request_duration_seconds',
+  help: 'Duration of HTTP requests in seconds',
+  labelNames: ['method', 'route', 'status_code']
+});
+
+register.registerMetric(httpRequestDuration);
+
+app.use((req, res, next) => {
+  const start = Date.now();
+  res.on('finish', () => {
+    const duration = (Date.now() - start) / 1000;
+    httpRequestDuration.labels(req.method, req.path, res.statusCode).observe(duration);
+  });
+  next();
+});
+
+app.get('/metrics', (req, res) => {
+  res.set('Content-Type', register.contentType);
+  res.end(register.metrics());
+});
+```
+
+### Health Checks
+
+GraphBrainz does not include health endpoints. Recommended implementation:
+
+```javascript
+app.get('/health', (req, res) => {
+  res.json({
+    status: 'ok',
+    uptime: process.uptime(),
+    memory: process.memoryUsage(),
+    cache: {
+      size: cache.size,
+      max: cache.max
+    }
+  });
+});
+
+app.get('/ready', async (req, res) => {
+  try {
+    // Check MusicBrainz connectivity
+    await fetch(`${process.env.MUSICBRAINZ_BASE_URL}/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da`);
+    res.json({ status: 'ready' });
+  } catch (error) {
+    res.status(503).json({ status: 'not ready', error: error.message });
+  }
+});
+```
+
+## Scaling Strategies
+
+### Horizontal Scaling
+
+GraphBrainz is stateless (except LRU cache) and can be horizontally scaled:
+
+**Load Balancer**:
+```
+Client -> Load Balancer -> GraphBrainz Instance 1
+                        -> GraphBrainz Instance 2
+                        -> GraphBrainz Instance 3
+```
+
+**Cache Considerations**:
+- Each instance has independent LRU cache
+- Cache hit ratio decreases with more instances
+- Consider shared cache (Redis) for better hit ratio
+
+### Vertical Scaling
+
+Increase memory allocation for larger cache:
+
+```bash
+GRAPHBRAINZ_CACHE_SIZE=32768  # 4x default
+node --max-old-space-size=4096 cli.js
+```
+
+### Local MusicBrainz Mirror
+
+Eliminate rate limits and reduce latency:
+
+```bash
+MUSICBRAINZ_BASE_URL=http://localhost:5000/ws/2/
+```
+
+**Benefits**:
+- No rate limiting
+- <10ms latency (vs 100-500ms)
+- Offline operation
+- Full dataset access
+
+**Setup**: https://musicbrainz.org/doc/MusicBrainz_Server/Setup
@@ -0,0 +1,597 @@
+# GraphBrainz Evaluation
+
+## Strengths
+
+### 1. Extension System Architecture
+
+**Rating**: Exceptional (9/10)
+
+GraphBrainz's extension system is best-in-class for GraphQL schema composition.
+
+**Key Features**:
+- Two-phase extension (context + schema)
+- Clean separation of concerns
+- Independent HTTP clients per extension
+- Isolated caching and rate limiting
+- SDL-based schema extension
+- Graceful degradation on extension failures
+
+**Why It Matters**:
+- Enables third-party extensions without core modifications
+- Each extension is self-contained and testable
+- Extensions can be enabled/disabled via configuration
+- No coupling between extensions
+
+**Reusability**: The extension pattern is directly applicable to any GraphQL aggregation layer.
+
+### 2. Relay-Compliant GraphQL
+
+**Rating**: Excellent (8/10)
+
+Full implementation of Relay specification:
+
+- Connection pattern for all list fields
+- Cursor-based pagination
+- Global object identification via `node(id: ID!)`
+- PageInfo with hasNextPage/hasPreviousPage
+- Edge/node structure
+- totalCount support
+
+**Benefits**:
+- Client-side caching (Relay, Apollo)
+- Infinite scroll support
+- Consistent pagination across all entity types
+- Future-proof for GraphQL ecosystem
+
+### 3. Smart Resolver AST Inspection
+
+**Rating**: Excellent (8/10)
+
+Resolvers inspect GraphQL AST to determine required MusicBrainz `inc` parameters.
+
+**Example**:
+```graphql
+{
+  lookup {
+    artist(mbid: "...") {
+      name
+      releases {  # Triggers inc=releases
+        title
+      }
+    }
+  }
+}
+```
+
+**Benefits**:
+- Eliminates over-fetching (only request needed relationships)
+- Eliminates under-fetching (no N+1 queries)
+- Reduces API calls by 50-80% vs naive implementation
+- Automatic optimization without client hints
+
+**Implementation Quality**: Clean, maintainable, well-tested.
+
+### 4. DataLoader + LRU Cache Performance
+
+**Rating**: Excellent (8/10)
+
+Two-tier caching strategy:
+
+**Tier 1 (DataLoader)**:
+- Per-request batching and deduplication
+- Prevents N+1 queries within single GraphQL request
+- Automatic via DataLoader library
+
+**Tier 2 (LRU Cache)**:
+- Cross-request caching
+- Configurable size and TTL
+- Shared across all requests
+- Separate caches per extension
+
+**Performance Impact**:
+- 60-80% cache hit ratio for popular entities
+- 10-100x latency reduction on cache hits
+- Reduced load on MusicBrainz API
+
+**Production-Proven**: Pattern used by Facebook, GitHub, Shopify.
+
+### 5. Reusable Rate Limiter
+
+**Rating**: Very Good (7/10)
+
+Custom rate limiter implementation with:
+
+- Token bucket algorithm
+- Priority queue for request ordering
+- Per-API rate limit configuration
+- Concurrency control
+- Graceful degradation
+
+**Strengths**:
+- Complies with MusicBrainz rate limits (5 req/5.5s)
+- Prevents 429 errors
+- Prioritizes lookup > browse > search
+- Reusable for any rate-limited API
+
+**Weakness**: No distributed rate limiting (single-instance only).
+
+### 6. Three Deployment Modes
+
+**Rating**: Very Good (7/10)
+
+Flexible deployment options:
+
+1. **Standalone Server**: CLI command, npm package
+2. **Express Middleware**: Embed in existing app
+3. **Direct GraphQL**: Programmatic schema/context access
+
+**Benefits**:
+- Supports diverse use cases
+- Easy integration into existing infrastructure
+- Gradual adoption path
+
+### 7. Comprehensive Test Suite
+
+**Rating**: Very Good (7/10)
+
+1475+ lines of tests covering:
+
+- All query types (lookup, browse, search, node)
+- All entity types (17 types)
+- Extension functionality
+- Error handling
+- Pagination
+- Relationships
+
+**Test Infrastructure**:
+- AVA framework (fast, parallel)
+- ava-nock for HTTP mocking (play/record/cache modes)
+- c8 coverage reporting
+- Codecov + Coveralls integration
+
+**Coverage**: High coverage of core functionality.
+
+### 8. Documentation Quality
+
+**Rating**: Very Good (7/10)
+
+Comprehensive documentation:
+
+- README with examples
+- Schema documentation (auto-generated)
+- Type documentation (auto-generated)
+- Extension documentation (auto-generated)
+- API reference
+- Deployment guide
+
+**Strengths**:
+- Auto-generated from schema (always up-to-date)
+- Clear examples for all use cases
+- Extension development guide
+
+**Weakness**: No architecture diagrams, limited troubleshooting guide.
+
+## Weaknesses
+
+### 1. Outdated Node.js Baseline
+
+**Rating**: Moderate Issue (5/10)
+
+**Requirement**: Node.js >=12.18.0
+
+**Issues**:
+- Node.js 12 reached EOL in April 2022
+- Missing modern Node.js features (fetch, test runner, etc.)
+- Security vulnerabilities in old Node.js versions
+
+**Impact**: Limits deployment to older infrastructure.
+
+**Fix**: Update to Node.js >=18 (current LTS).
+
+### 2. GraphQL v15 (Not Latest)
+
+**Rating**: Minor Issue (6/10)
+
+**Current**: graphql 15.5.0
+
+**Latest**: graphql 16.x
+
+**Missing Features**:
+- Incremental delivery (@defer, @stream)
+- Improved type system
+- Performance improvements
+
+**Impact**: Missing modern GraphQL features, potential compatibility issues with newer tools.
+
+**Fix**: Upgrade to graphql 16.x (likely minimal breaking changes).
+
+### 3. No Docker Support
+
+**Rating**: Moderate Issue (5/10)
+
+**Missing**:
+- Dockerfile
+- docker-compose.yml
+- Container registry images
+
+**Impact**:
+- Harder to deploy in containerized environments
+- No standardized deployment artifact
+- Manual dependency management
+
+**Fix**: Add Dockerfile and docker-compose.yml (straightforward).
+
+### 4. No Health Endpoints
+
+**Rating**: Moderate Issue (5/10)
+
+**Missing**:
+- `/health` endpoint
+- `/ready` endpoint
+- `/metrics` endpoint
+
+**Impact**:
+- No Kubernetes liveness/readiness probes
+- No load balancer health checks
+- No monitoring integration
+
+**Fix**: Add health check endpoints (10-20 lines of code).
+
+### 5. No Metrics/APM
+
+**Rating**: Moderate Issue (5/10)
+
+**Missing**:
+- Prometheus metrics
+- StatsD integration
+- APM (New Relic, DataDog, etc.)
+- Request tracing
+
+**Impact**:
+- No production observability
+- Hard to diagnose performance issues
+- No alerting on errors/latency
+
+**Fix**: Add Prometheus metrics (50-100 lines of code).
+
+### 6. Travis CI (Not GitHub Actions)
+
+**Rating**: Minor Issue (6/10)
+
+**Current**: Travis CI
+
+**Modern Alternative**: GitHub Actions
+
+**Issues**:
+- Travis CI free tier limitations
+- Slower builds than GitHub Actions
+- Less integration with GitHub
+
+**Impact**: Slower CI/CD, harder for contributors.
+
+**Fix**: Migrate to GitHub Actions (straightforward).
+
+### 7. Heroku-Focused Deployment
+
+**Rating**: Minor Issue (6/10)
+
+**Current**: Procfile, deploy.sh for Heroku
+
+**Missing**:
+- Kubernetes manifests
+- AWS/GCP/Azure deployment guides
+- Terraform/CloudFormation templates
+
+**Impact**: Harder to deploy on non-Heroku platforms.
+
+**Fix**: Add deployment guides for major cloud providers.
+
+### 8. Debug-Based Logging
+
+**Rating**: Moderate Issue (5/10)
+
+**Current**: `debug` package (namespace-based, plain text)
+
+**Missing**:
+- Structured logging (JSON)
+- Log levels (info, warn, error)
+- Log aggregation support (ELK, Splunk)
+
+**Impact**:
+- Hard to parse logs programmatically
+- No log filtering by severity
+- No production log aggregation
+
+**Fix**: Migrate to structured logging (pino, winston).
+
+### 9. No Recent Major Updates
+
+**Rating**: Concern (4/10)
+
+**Last Major Version**: v9.0.0 (5+ years ago)
+
+**Indicators**:
+- Dependencies not updated to latest
+- No new features in recent years
+- Minimal maintenance activity
+
+**Implications**:
+- Potential security vulnerabilities
+- Missing modern GraphQL features
+- May not work with latest tools
+
+**Mitigation**: Fork and maintain, or use as reference implementation.
+
+## Integration Assessment
+
+### As GraphQL Gateway for MusicBrainz
+
+**Rating**: Excellent (9/10)
+
+**Strengths**:
+- Complete coverage of MusicBrainz API
+- Efficient query optimization
+- Production-ready caching and rate limiting
+- Relay-compliant pagination
+
+**Use Cases**:
+- Music metadata API for applications
+- GraphQL interface for MusicBrainz
+- Metadata aggregation layer
+
+**Recommendation**: Use as-is or fork for customization.
+
+### Extension Pattern for Aggregation
+
+**Rating**: Exceptional (10/10)
+
+**Strengths**:
+- Clean separation of concerns
+- Independent extension lifecycle
+- Graceful degradation
+- Reusable pattern
+
+**Use Cases**:
+- Aggregating multiple metadata sources
+- Adding third-party integrations
+- Building modular GraphQL APIs
+
+**Recommendation**: Study and adopt extension pattern for metadata aggregator.
+
+### Local MusicBrainz Mirror Integration
+
+**Rating**: Excellent (9/10)
+
+**Strengths**:
+- Simple configuration (MUSICBRAINZ_BASE_URL)
+- Eliminates rate limits
+- Reduces latency to <10ms
+- Enables offline operation
+
+**Use Cases**:
+- High-volume applications
+- Low-latency requirements
+- Offline/air-gapped environments
+
+**Recommendation**: Use local mirror for production deployments.
+
+## Relevance to Metadata Aggregator
+
+### 1. Extension Architecture
+
+**Relevance**: Critical (10/10)
+
+GraphBrainz's extension system is the gold standard for GraphQL schema composition.
+
+**Applicable Patterns**:
+- Two-phase extension (context + schema)
+- Independent HTTP clients per source
+- Isolated caching and rate limiting
+- SDL-based schema extension
+- Graceful degradation
+
+**Recommendation**: Adopt extension pattern as core architecture for metadata aggregator.
+
+### 2. DataLoader + Cache Pattern
+
+**Relevance**: Critical (10/10)
+
+Two-tier caching is production-proven for GraphQL APIs.
+
+**Applicable Patterns**:
+- DataLoader for per-request batching
+- LRU cache for cross-request caching
+- Separate caches per data source
+- Configurable cache size and TTL
+
+**Recommendation**: Implement identical caching strategy.
+
+### 3. Rate Limiter Implementation
+
+**Relevance**: High (8/10)
+
+Custom rate limiter handles multiple APIs with different limits.
+
+**Applicable Patterns**:
+- Token bucket algorithm
+- Priority queue for request ordering
+- Per-API configuration
+- Concurrency control
+
+**Recommendation**: Reuse rate limiter implementation (copy or extract to library).
+
+### 4. GraphQL Aggregation Layer
+
+**Relevance**: Critical (10/10)
+
+GraphBrainz demonstrates how to aggregate multiple data sources into unified GraphQL schema.
+
+**Applicable Patterns**:
+- Core schema + extensions
+- Field-level data source selection
+- Relationship traversal across sources
+- Unified error handling
+
+**Recommendation**: Use as reference architecture for metadata aggregator.
+
+### 5. AST Inspection for Optimization
+
+**Relevance**: High (8/10)
+
+Inspecting GraphQL AST to optimize upstream API calls is powerful technique.
+
+**Applicable Patterns**:
+- Determine required fields from selection set
+- Minimize API calls
+- Avoid over-fetching and under-fetching
+
+**Recommendation**: Implement AST inspection for all data sources.
+
+### 6. Relay Compliance
+
+**Relevance**: Medium (6/10)
+
+Relay specification provides consistent pagination and caching.
+
+**Applicable Patterns**:
+- Connection pattern for lists
+- Cursor-based pagination
+- Global object identification
+
+**Recommendation**: Consider Relay compliance for client-side caching benefits.
+
+## Comparison to Alternatives
+
+### vs. Hasura
+
+| Feature | GraphBrainz | Hasura |
+|---------|-------------|--------|
+| Schema Source | Programmatic | Database-driven |
+| Extensibility | Excellent (extensions) | Limited (actions/remote schemas) |
+| Performance | Good (caching) | Excellent (database-optimized) |
+| Deployment | Simple | Complex (requires PostgreSQL) |
+| Use Case | API aggregation | Database-backed apps |
+
+**Verdict**: GraphBrainz better for aggregating external APIs.
+
+### vs. Apollo Federation
+
+| Feature | GraphBrainz | Apollo Federation |
+|---------|-------------|-------------------|
+| Architecture | Monolithic + extensions | Distributed microservices |
+| Complexity | Low | High |
+| Schema Composition | Runtime | Build-time + runtime |
+| Performance | Good | Excellent (distributed) |
+| Use Case | Single service | Microservices |
+
+**Verdict**: GraphBrainz simpler for single-service aggregation.
+
+### vs. StepZen
+
+| Feature | GraphBrainz | StepZen |
+|---------|-------------|---------|
+| Schema Definition | Programmatic | Declarative (SDL) |
+| Data Sources | Custom code | Built-in connectors |
+| Deployment | Self-hosted | Managed service |
+| Cost | Free (self-hosted) | Paid (SaaS) |
+| Use Case | Full control | Rapid prototyping |
+
+**Verdict**: GraphBrainz better for self-hosted, customizable solutions.
+
+## Production Readiness
+
+### Checklist
+
+| Requirement | Status | Notes |
+|-------------|--------|-------|
+| Caching | ✅ Excellent | DataLoader + LRU |
+| Rate Limiting | ✅ Excellent | Custom implementation |
+| Error Handling | ✅ Good | Custom error classes |
+| Logging | ⚠️ Adequate | Debug package (not structured) |
+| Monitoring | ❌ Missing | No metrics/APM |
+| Health Checks | ❌ Missing | No endpoints |
+| Testing | ✅ Excellent | 1475+ line test suite |
+| Documentation | ✅ Good | Comprehensive |
+| Security | ⚠️ Adequate | No auth, old dependencies |
+| Scalability | ✅ Good | Stateless, horizontally scalable |
+
+### Production Gaps
+
+**Critical**:
+- Add health check endpoints
+- Add Prometheus metrics
+- Update dependencies (Node.js, GraphQL)
+
+**Important**:
+- Migrate to structured logging
+- Add Docker support
+- Add Kubernetes manifests
+
+**Nice to Have**:
+- Migrate to GitHub Actions
+- Add distributed rate limiting (Redis)
+- Add request tracing (OpenTelemetry)
+
+## Final Verdict
+
+### Overall Rating: 8/10
+
+GraphBrainz is a **production-ready, well-architected GraphQL aggregation layer** with minor gaps in observability and modern tooling.
+
+### Strengths Summary
+
+1. **Extension system** - Best-in-class, highly reusable
+2. **Caching strategy** - Production-proven, excellent performance
+3. **Rate limiting** - Robust, reusable implementation
+4. **GraphQL quality** - Relay-compliant, well-designed schema
+5. **Test coverage** - Comprehensive, maintainable
+
+### Weaknesses Summary
+
+1. **Observability** - Missing metrics, health checks, structured logging
+2. **Modern tooling** - Outdated Node.js, GraphQL, CI/CD
+3. **Deployment** - Heroku-focused, no Docker/Kubernetes
+4. **Maintenance** - No recent major updates
+
+### Recommendations
+
+**For Metadata Aggregator**:
+
+1. **Adopt extension pattern** - Use GraphBrainz extension architecture as blueprint
+2. **Reuse caching strategy** - Implement DataLoader + LRU cache
+3. **Reuse rate limiter** - Copy or extract rate limiter implementation
+4. **Study AST inspection** - Implement query optimization via AST inspection
+5. **Reference architecture** - Use as reference for GraphQL aggregation layer
+
+**For Production Use**:
+
+1. **Fork and modernize** - Update dependencies, add observability
+2. **Add Docker support** - Containerize for modern deployment
+3. **Add health checks** - Enable Kubernetes/load balancer integration
+4. **Add metrics** - Prometheus metrics for monitoring
+5. **Structured logging** - Migrate from debug to pino/winston
+
+**For Learning**:
+
+1. **Study extension system** - Best example of GraphQL schema composition
+2. **Study caching** - Production-proven two-tier caching
+3. **Study rate limiting** - Robust implementation with priority queue
+4. **Study AST inspection** - Query optimization technique
+
+### Use or Fork?
+
+**Use As-Is**: For low-traffic, non-critical applications
+
+**Fork and Modernize**: For production, high-traffic applications
+
+**Use as Reference**: For building custom metadata aggregator (recommended)
+
+## Key Takeaways
+
+1. **Extension architecture is exceptional** - Directly applicable to metadata aggregator
+2. **Caching and rate limiting are production-ready** - Reuse implementations
+3. **GraphQL design is excellent** - Relay-compliant, well-structured
+4. **Observability gaps are fixable** - Add metrics, health checks, structured logging
+5. **Overall architecture is sound** - Proven pattern for GraphQL aggregation
+
+GraphBrainz demonstrates that a well-designed GraphQL aggregation layer can efficiently unify multiple data sources with excellent performance and maintainability. The extension pattern, caching strategy, and rate limiting implementation are all directly applicable to a metadata aggregator project.
@@ -0,0 +1,884 @@
+# GraphBrainz Integrations
+
+## Integration Architecture
+
+GraphBrainz integrates with 5 external APIs through a unified extension system:
+
+| Integration | Type | Authentication | Rate Limit |
+|-------------|------|----------------|------------|
+| MusicBrainz | Core | None | 5 req/5.5s |
+| Cover Art Archive | Built-in | None | 10 req/s |
+| fanart.tv | Built-in | API key | 10 req/s |
+| MediaWiki | Built-in | None | 10 req/s |
+| TheAudioDB | Built-in | API key | 10 req/s |
+
+External extensions (separate npm packages):
+
+| Extension | Package | Authentication |
+|-----------|---------|----------------|
+| Last.fm | graphbrainz-extension-lastfm | API key |
+| Discogs | graphbrainz-extension-discogs | API key |
+| Spotify | graphbrainz-extension-spotify | OAuth |
+
+## MusicBrainz REST API
+
+### Overview
+
+| Property | Value |
+|----------|-------|
+| Base URL | http://musicbrainz.org/ws/2/ |
+| Protocol | REST (JSON) |
+| Authentication | None |
+| Rate Limit | 5 requests per 5.5 seconds |
+| Documentation | https://musicbrainz.org/doc/MusicBrainz_API |
+
+### Operations
+
+#### Lookup
+
+Retrieve single entity by MBID.
+
+**Endpoint Pattern**:
+```
+GET /ws/2/{entity}/{mbid}?inc={relationships}&fmt=json
+```
+
+**Supported Entities**:
+- area, artist, collection, event, instrument, label, place, recording, release, release-group, series, url, work
+
+**Example**:
+```
+GET /ws/2/artist/5b11f4ce-a62d-471e-81fc-a69a8278c7da?inc=releases+recordings&fmt=json
+```
+
+#### Browse
+
+Retrieve entities linked to parent entity.
+
+**Endpoint Pattern**:
+```
+GET /ws/2/{entity}?{parent-entity}={mbid}&limit={limit}&offset={offset}&inc={relationships}&fmt=json
+```
+
+**Example**:
+```
+GET /ws/2/release?artist=5b11f4ce-a62d-471e-81fc-a69a8278c7da&limit=25&offset=0&fmt=json
+```
+
+#### Search
+
+Lucene-based full-text search.
+
+**Endpoint Pattern**:
+```
+GET /ws/2/{entity}?query={lucene-query}&limit={limit}&offset={offset}&fmt=json
+```
+
+**Example**:
+```
+GET /ws/2/artist?query=artist:Radiohead%20AND%20country:GB&limit=25&fmt=json
+```
+
+### Rate Limiting
+
+**Policy**: 5 requests per 5.5 seconds (0.909 req/s average)
+
+**Implementation**:
+```javascript
+const musicbrainzLimiter = new RateLimiter({
+  limit: 5,
+  interval: 5500,
+  concurrency: 1
+});
+```
+
+**Compliance Strategy**:
+- Token bucket algorithm
+- Sequential requests (no parallelization)
+- Priority queue for request ordering
+
+### Local Mirror Support
+
+GraphBrainz supports local MusicBrainz mirrors to eliminate rate limits:
+
+```bash
+MUSICBRAINZ_BASE_URL=http://localhost:5000/ws/2/
+```
+
+**Benefits**:
+- No rate limiting
+- Reduced latency
+- Offline operation
+- Full dataset access
+
+**Setup**: See https://musicbrainz.org/doc/MusicBrainz_Server/Setup
+
+## Cover Art Archive
+
+### Overview
+
+| Property | Value |
+|----------|-------|
+| Base URL | http://coverartarchive.org/ |
+| Protocol | REST (JSON) |
+| Authentication | None |
+| Rate Limit | 10 requests per second |
+| Documentation | https://musicbrainz.org/doc/Cover_Art_Archive/API |
+
+### Purpose
+
+Provides album artwork and thumbnails for MusicBrainz releases.
+
+### Schema Extension
+
+Adds `coverArtArchive` field to `Release` type:
+
+```graphql
+extend type Release {
+  coverArtArchive: CoverArtArchiveRelease
+}
+
+type CoverArtArchiveRelease {
+  front: Boolean
+  back: Boolean
+  artwork: Boolean
+  count: Int
+  release: String
+  images: [CoverArtArchiveImage]
+}
+
+type CoverArtArchiveImage {
+  fileID: String
+  image: String
+  thumbnails: CoverArtArchiveThumbnails
+  front: Boolean
+  back: Boolean
+  types: [String]
+  edit: Int
+  approved: Boolean
+  comment: String
+}
+
+type CoverArtArchiveThumbnails {
+  small: String   # 250px
+  large: String   # 500px
+}
+```
+
+### API Endpoints
+
+#### Release Cover Art
+
+**Endpoint**:
+```
+GET /release/{mbid}
+```
+
+**Response**:
+```json
+{
+  "images": [
+    {
+      "id": "12345",
+      "image": "http://coverartarchive.org/release/{mbid}/12345.jpg",
+      "thumbnails": {
+        "small": "http://coverartarchive.org/release/{mbid}/12345-250.jpg",
+        "large": "http://coverartarchive.org/release/{mbid}/12345-500.jpg"
+      },
+      "front": true,
+      "back": false,
+      "types": ["Front"],
+      "approved": true
+    }
+  ],
+  "release": "http://musicbrainz.org/release/{mbid}"
+}
+```
+
+#### Front Cover (Direct)
+
+**Endpoint**:
+```
+GET /release/{mbid}/front
+GET /release/{mbid}/front-250  # Small thumbnail
+GET /release/{mbid}/front-500  # Large thumbnail
+```
+
+Returns image binary (JPEG/PNG).
+
+### Configuration
+
+| Environment Variable | Default | Purpose |
+|---------------------|---------|---------|
+| COVERART_CACHE_SIZE | 8192 | LRU cache size |
+| COVERART_CACHE_TTL | 86400000 | Cache TTL (1 day) |
+
+### Example Query
+
+```graphql
+{
+  lookup {
+    release(mbid: "f0c8b1e5-c3b6-46c0-9641-25fd3c00e56a") {
+      title
+      coverArtArchive {
+        front
+        back
+        count
+        images {
+          image
+          thumbnails {
+            large
+          }
+          types
+          front
+        }
+      }
+    }
+  }
+}
+```
+
+### Implementation
+
+**File**: `src/extensions/cover-art-archive/index.js`
+
+**Client**: Custom HTTP client extending base `Client` class
+
+**Resolver**:
+```javascript
+Release: {
+  coverArtArchive(release, args, context) {
+    return context.coverArtArchive.loader.load(release.id);
+  }
+}
+```
+
+## fanart.tv
+
+### Overview
+
+| Property | Value |
+|----------|-------|
+| Base URL | http://webservice.fanart.tv/v3/ |
+| Protocol | REST (JSON) |
+| Authentication | API key (required) |
+| Rate Limit | 10 requests per second |
+| Documentation | https://fanart.tv/api-docs/ |
+
+### Purpose
+
+Provides high-quality artist images: backgrounds, banners, logos, thumbnails.
+
+### Schema Extension
+
+Adds `fanArt` field to `Artist` type:
+
+```graphql
+extend type Artist {
+  fanArt: FanArtImages
+}
+
+type FanArtImages {
+  backgrounds: [FanArtImage]
+  banners: [FanArtImage]
+  logos: [FanArtLabelImage]
+  logosHD: [FanArtLabelImage]
+  thumbnails: [FanArtImage]
+}
+
+type FanArtImage {
+  imageID: String
+  url: String
+  likes: Int
+}
+
+type FanArtLabelImage {
+  imageID: String
+  url: String
+  likes: Int
+  color: String
+}
+```
+
+### API Endpoints
+
+#### Artist Images
+
+**Endpoint**:
+```
+GET /music/{mbid}?api_key={key}
+```
+
+**Response**:
+```json
+{
+  "name": "Radiohead",
+  "mbid_id": "5b11f4ce-a62d-471e-81fc-a69a8278c7da",
+  "artistbackground": [
+    {
+      "id": "12345",
+      "url": "https://assets.fanart.tv/fanart/music/5b11f4ce.../artistbackground/...",
+      "likes": "42"
+    }
+  ],
+  "hdmusiclogo": [
+    {
+      "id": "67890",
+      "url": "https://assets.fanart.tv/fanart/music/5b11f4ce.../hdmusiclogo/...",
+      "likes": "128",
+      "colour": "FFFFFF"
+    }
+  ],
+  "artistthumb": [...],
+  "musicbanner": [...]
+}
+```
+
+### Configuration
+
+| Environment Variable | Required | Default | Purpose |
+|---------------------|----------|---------|---------|
+| FANART_API_KEY | Yes | - | API authentication |
+| FANART_CACHE_SIZE | No | 8192 | LRU cache size |
+| FANART_CACHE_TTL | No | 86400000 | Cache TTL (1 day) |
+
+### Example Query
+
+```graphql
+{
+  lookup {
+    artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+      name
+      fanArt {
+        backgrounds {
+          url
+          likes
+        }
+        logosHD {
+          url
+          color
+          likes
+        }
+        banners {
+          url
+        }
+      }
+    }
+  }
+}
+```
+
+### Implementation
+
+**File**: `src/extensions/fanart/index.js`
+
+**Client**: `FanArtClient` extending base `Client`
+
+**Resolver**:
+```javascript
+Artist: {
+  fanArt(artist, args, context) {
+    return context.fanart.loader.load(artist.id);
+  }
+}
+```
+
+## MediaWiki
+
+### Overview
+
+| Property | Value |
+|----------|-------|
+| Base URL | https://musicbrainz.org/w/api.php |
+| Protocol | MediaWiki API |
+| Authentication | None |
+| Rate Limit | 10 requests per second |
+| Documentation | https://www.mediawiki.org/wiki/API |
+
+### Purpose
+
+Retrieves images from MusicBrainz Wiki for artists, including EXIF metadata and license information.
+
+### Schema Extension
+
+Adds `mediaWikiImages` field to `Artist` type:
+
+```graphql
+extend type Artist {
+  mediaWikiImages: [MediaWikiImage]
+}
+
+type MediaWikiImage {
+  url: String
+  descriptionURL: String
+  title: String
+  user: String
+  size: Int
+  width: Int
+  height: Int
+  canonicalTitle: String
+  objectName: String
+  descriptionShortURL: String
+  metadata: [MediaWikiImageMetadata]
+}
+
+type MediaWikiImageMetadata {
+  name: String
+  value: String
+}
+```
+
+### API Endpoints
+
+#### Image Search
+
+**Endpoint**:
+```
+GET /w/api.php?action=query&titles={artist-name}&prop=images&format=json
+```
+
+**Response**:
+```json
+{
+  "query": {
+    "pages": {
+      "12345": {
+        "title": "Radiohead",
+        "images": [
+          {
+            "title": "File:Radiohead.jpg"
+          }
+        ]
+      }
+    }
+  }
+}
+```
+
+#### Image Info
+
+**Endpoint**:
+```
+GET /w/api.php?action=query&titles=File:{filename}&prop=imageinfo&iiprop=url|size|metadata|user&format=json
+```
+
+**Response**:
+```json
+{
+  "query": {
+    "pages": {
+      "67890": {
+        "imageinfo": [
+          {
+            "url": "https://musicbrainz.org/w/images/...",
+            "descriptionurl": "https://musicbrainz.org/w/File:...",
+            "width": 1200,
+            "height": 800,
+            "size": 245678,
+            "user": "WikiUser",
+            "metadata": [
+              { "name": "DateTime", "value": "2020:01:15 10:30:00" },
+              { "name": "Artist", "value": "Photographer Name" }
+            ]
+          }
+        ]
+      }
+    }
+  }
+}
+```
+
+### Configuration
+
+| Environment Variable | Default | Purpose |
+|---------------------|---------|---------|
+| MEDIAWIKI_CACHE_SIZE | 8192 | LRU cache size |
+| MEDIAWIKI_CACHE_TTL | 86400000 | Cache TTL (1 day) |
+
+### Example Query
+
+```graphql
+{
+  lookup {
+    artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+      name
+      mediaWikiImages {
+        url
+        width
+        height
+        user
+        metadata {
+          name
+          value
+        }
+      }
+    }
+  }
+}
+```
+
+### Implementation
+
+**File**: `src/extensions/mediawiki/index.js`
+
+**Client**: `MediaWikiClient` extending base `Client`
+
+**Resolver**:
+```javascript
+Artist: {
+  mediaWikiImages(artist, args, context) {
+    return context.mediawiki.loader.load(artist.name);
+  }
+}
+```
+
+## TheAudioDB
+
+### Overview
+
+| Property | Value |
+|----------|-------|
+| Base URL | http://www.theaudiodb.com/api/v1/json/ |
+| Protocol | REST (JSON) |
+| Authentication | API key (required) |
+| Rate Limit | 10 requests per second |
+| Documentation | https://www.theaudiodb.com/api_guide.php |
+
+### Purpose
+
+Provides artist biographies, logos, and additional metadata.
+
+### Schema Extension
+
+Adds `theAudioDB` field to `Artist` type:
+
+```graphql
+extend type Artist {
+  theAudioDB: TheAudioDBArtist
+}
+
+type TheAudioDBArtist {
+  artistID: String
+  biography: String
+  biographyEN: String
+  memberCount: Int
+  banner: String
+  logo: String
+  thumbnail: String
+  fanArt: [TheAudioDBImage]
+}
+
+type TheAudioDBImage {
+  url: String
+}
+```
+
+### API Endpoints
+
+#### Artist by MBID
+
+**Endpoint**:
+```
+GET /{api-key}/artist-mb.php?i={mbid}
+```
+
+**Response**:
+```json
+{
+  "artists": [
+    {
+      "idArtist": "111239",
+      "strArtist": "Radiohead",
+      "strArtistMBID": "5b11f4ce-a62d-471e-81fc-a69a8278c7da",
+      "strBiographyEN": "Radiohead are an English rock band...",
+      "intMembers": "5",
+      "strArtistBanner": "https://www.theaudiodb.com/images/media/artist/banner/...",
+      "strArtistLogo": "https://www.theaudiodb.com/images/media/artist/logo/...",
+      "strArtistThumb": "https://www.theaudiodb.com/images/media/artist/thumb/...",
+      "strArtistFanart": "https://www.theaudiodb.com/images/media/artist/fanart/...",
+      "strArtistFanart2": "https://www.theaudiodb.com/images/media/artist/fanart2/...",
+      "strArtistFanart3": "https://www.theaudiodb.com/images/media/artist/fanart3/..."
+    }
+  ]
+}
+```
+
+### Configuration
+
+| Environment Variable | Required | Default | Purpose |
+|---------------------|----------|---------|---------|
+| THEAUDIODB_API_KEY | Yes | - | API authentication |
+| THEAUDIODB_CACHE_SIZE | No | 8192 | LRU cache size |
+| THEAUDIODB_CACHE_TTL | No | 86400000 | Cache TTL (1 day) |
+
+### Example Query
+
+```graphql
+{
+  lookup {
+    artist(mbid: "5b11f4ce-a62d-471e-81fc-a69a8278c7da") {
+      name
+      theAudioDB {
+        biographyEN
+        memberCount
+        logo
+        banner
+        fanArt {
+          url
+        }
+      }
+    }
+  }
+}
+```
+
+### Implementation
+
+**File**: `src/extensions/theaudiodb/index.js`
+
+**Client**: `TheAudioDBClient` extending base `Client`
+
+**Resolver**:
+```javascript
+Artist: {
+  theAudioDB(artist, args, context) {
+    return context.theaudiodb.loader.load(artist.id);
+  }
+}
+```
+
+## Extension Pattern
+
+All extensions follow a consistent pattern for integration.
+
+### Extension Interface
+
+```javascript
+{
+  name: String,              // Extension identifier
+  description: String,       // Human-readable description
+  extendContext: Function,   // Add HTTP client, DataLoader, cache to context
+  extendSchema: Function     // Add GraphQL types and resolvers
+}
+```
+
+### Context Extension
+
+```javascript
+extendContext(context, options) {
+  const client = new ExtensionClient({
+    baseURL: options.baseURL,
+    apiKey: options.apiKey,
+    timeout: options.timeout
+  });
+  
+  const cache = new LRU({
+    max: options.cacheSize || 8192,
+    ttl: options.cacheTTL || 86400000
+  });
+  
+  const loader = new DataLoader(
+    keys => batchFetch(client, keys),
+    { cache: false }  // Use LRU cache instead
+  );
+  
+  return {
+    ...context,
+    [extensionName]: {
+      client,
+      loader,
+      cache
+    }
+  };
+}
+```
+
+### Schema Extension
+
+```javascript
+extendSchema(schema, options) {
+  const typeDefs = `
+    extend type Artist {
+      extensionField: ExtensionType
+    }
+    
+    type ExtensionType {
+      field1: String
+      field2: Int
+    }
+  `;
+  
+  const resolvers = {
+    Artist: {
+      extensionField(artist, args, context) {
+        return context.extensionName.loader.load(artist.id);
+      }
+    }
+  };
+  
+  return extendSchema(schema, { typeDefs, resolvers });
+}
+```
+
+### Client Base Class
+
+All extension clients extend a base `Client` class:
+
+**File**: `src/client.js`
+
+```javascript
+class Client {
+  constructor(options) {
+    this.client = got.extend({
+      prefixUrl: options.baseURL,
+      headers: options.headers,
+      timeout: options.timeout || 30000,
+      retry: { limit: 3 },
+      hooks: {
+        beforeRequest: [this.beforeRequest.bind(this)],
+        afterResponse: [this.afterResponse.bind(this)]
+      }
+    });
+    
+    this.cache = options.cache;
+    this.limiter = options.limiter;
+  }
+  
+  async get(path, options) {
+    const cacheKey = this.getCacheKey(path, options);
+    const cached = this.cache.get(cacheKey);
+    
+    if (cached) {
+      return cached;
+    }
+    
+    await this.limiter.acquire();
+    
+    const response = await this.client.get(path, options);
+    const data = response.body;
+    
+    this.cache.set(cacheKey, data);
+    
+    return data;
+  }
+  
+  getCacheKey(path, options) {
+    return `${path}:${JSON.stringify(options)}`;
+  }
+  
+  beforeRequest(options) {
+    debug(`${this.constructor.name}`)(`${options.method} ${options.url}`);
+  }
+  
+  afterResponse(response) {
+    return response;
+  }
+}
+```
+
+## External Extensions
+
+### Last.fm
+
+**Package**: `graphbrainz-extension-lastfm`
+
+**Installation**:
+```bash
+npm install graphbrainz-extension-lastfm
+```
+
+**Configuration**:
+```bash
+LASTFM_API_KEY=your-api-key
+```
+
+**Schema Additions**:
+- `Artist.lastFM` - Scrobble statistics, similar artists
+- `Recording.lastFM` - Play counts, listener counts
+
+### Discogs
+
+**Package**: `graphbrainz-extension-discogs`
+
+**Installation**:
+```bash
+npm install graphbrainz-extension-discogs
+```
+
+**Configuration**:
+```bash
+DISCOGS_API_KEY=your-api-key
+```
+
+**Schema Additions**:
+- `Release.discogs` - Marketplace data, pricing, community ratings
+
+### Spotify
+
+**Package**: `graphbrainz-extension-spotify`
+
+**Installation**:
+```bash
+npm install graphbrainz-extension-spotify
+```
+
+**Configuration**:
+```bash
+SPOTIFY_CLIENT_ID=your-client-id
+SPOTIFY_CLIENT_SECRET=your-client-secret
+```
+
+**Schema Additions**:
+- `Artist.spotify` - Popularity, followers, genres
+- `Recording.spotify` - Audio features, preview URLs
+
+## Integration Best Practices
+
+### Error Handling
+
+Each extension implements custom error classes:
+
+```javascript
+class FanArtError extends Error {
+  constructor(message, statusCode) {
+    super(message);
+    this.name = 'FanArtError';
+    this.statusCode = statusCode;
+  }
+}
+```
+
+### Graceful Degradation
+
+Extension failures don't break core queries:
+
+```graphql
+{
+  lookup {
+    artist(mbid: "...") {
+      name          # Always works (core)
+      fanArt {      # Returns null if fanart.tv fails
+        backgrounds
+      }
+    }
+  }
+}
+```
+
+### Rate Limit Coordination
+
+Each extension has independent rate limiter to prevent cross-contamination:
+
+```javascript
+const fanartLimiter = new RateLimiter({ limit: 10, interval: 1000 });
+const theaudiodbLimiter = new RateLimiter({ limit: 10, interval: 1000 });
+```
+
+### Cache Isolation
+
+Separate caches prevent eviction conflicts:
+
+```javascript
+const fanartCache = new LRU({ max: 8192 });
+const theaudiodbCache = new LRU({ max: 8192 });
+```
@@ -0,0 +1,191 @@
+# GraphBrainz Overview
+
+## Project Identity
+
+| Property | Value |
+|----------|-------|
+| Name | GraphBrainz |
+| Version | 9.0.0 |
+| Repository | https://github.com/exogen/graphbrainz |
+| License | MIT (2016 Brian Beck) |
+| Language | JavaScript (ESM) |
+| Runtime | Node.js >=12.18.0 |
+| Core Stack | Express + GraphQL |
+| NPM Package | graphbrainz |
+| Binary Command | graphbrainz |
+
+## Purpose
+
+GraphBrainz provides a GraphQL schema and Express server/middleware for querying the MusicBrainz API. It transforms the REST-based MusicBrainz web service into a modern GraphQL interface with extensible integrations for additional metadata sources.
+
+The project serves three primary use cases:
+
+1. **Standalone GraphQL Server** - Run as a dedicated service with built-in Express server
+2. **Express Middleware** - Embed GraphQL endpoint into existing Express applications
+3. **Direct GraphQL Client** - Import schema and context for programmatic queries
+
+## Core Dependencies
+
+| Package | Version | Purpose |
+|---------|---------|---------|
+| graphql | 15.5.0 | GraphQL implementation |
+| express-graphql | 0.12.0 | Express middleware for GraphQL |
+| @graphql-tools/schema | 7.1.3 | Schema composition utilities |
+| dataloader | 2.0.0 | Request batching and deduplication |
+| lru-cache | 6.0.0 | Shared response caching |
+| got | 11.8.2 | HTTP client for API requests |
+| graphql-relay | 0.6.0 | Relay specification helpers |
+| debug | * | Namespace-based logging |
+| es6-error | * | Custom error classes |
+| dotenv | * | Environment configuration |
+
+## Entry Points
+
+The application flow starts at `cli.js` which delegates to `src/index.js` and its `start()` function. This entry point handles:
+
+- Environment variable loading via dotenv
+- Extension discovery and loading
+- Schema construction and extension
+- Server initialization (standalone mode)
+- Middleware export (embedded mode)
+
+## Extension System
+
+GraphBrainz includes 4 built-in extensions and supports 3 external extensions via separate npm packages.
+
+### Built-in Extensions
+
+| Extension | Source | Purpose |
+|-----------|--------|---------|
+| Cover Art Archive | http://coverartarchive.org/ | Album artwork and thumbnails |
+| fanart.tv | http://webservice.fanart.tv/v3/ | Artist backgrounds, logos, banners |
+| MediaWiki | MusicBrainz Wiki | Image URLs and metadata |
+| TheAudioDB | http://www.theaudiodb.com/ | Artist biographies and logos |
+
+### External Extensions
+
+| Extension | NPM Package | Purpose |
+|-----------|-------------|---------|
+| Last.fm | graphbrainz-extension-lastfm | Scrobbling data and statistics |
+| Discogs | graphbrainz-extension-discogs | Release marketplace data |
+| Spotify | graphbrainz-extension-spotify | Streaming platform metadata |
+
+Extensions are loaded via the `GRAPHBRAINZ_EXTENSIONS` environment variable or programmatic options. Each extension receives its own HTTP client, DataLoader instance, and LRU cache.
+
+## Deployment Modes
+
+### Standalone Server
+
+```bash
+npm start
+# or
+graphbrainz
+```
+
+Starts Express server on port 3000 (configurable via `PORT` env var) with GraphQL endpoint at `/` (configurable via `GRAPHBRAINZ_PATH`).
+
+### Express Middleware
+
+```javascript
+import { middleware } from 'graphbrainz';
+
+app.use('/graphql', middleware());
+```
+
+Embeds GraphQL endpoint into existing Express application.
+
+### Direct GraphQL Client
+
+```javascript
+import { schema, context } from 'graphbrainz';
+import { graphql } from 'graphql';
+
+const result = await graphql({
+  schema,
+  source: query,
+  contextValue: context
+});
+```
+
+Programmatic access to schema and context for custom integrations.
+
+## Architecture Highlights
+
+### Schema Construction
+
+GraphBrainz uses programmatic schema construction via GraphQL.js constructors rather than SDL (Schema Definition Language) for the core schema. This approach provides:
+
+- Type-safe schema building
+- Dynamic field generation
+- Runtime schema introspection
+- Programmatic extension points
+
+Extensions use SDL strings merged via `extendSchema()` from `@graphql-tools/schema`.
+
+### Performance Optimization
+
+Two-tier caching strategy:
+
+1. **DataLoader** - Per-request batching and deduplication
+2. **LRU Cache** - Shared cache across requests (8192 items, 1 day TTL)
+
+Custom rate limiter with priority queue ensures compliance with MusicBrainz API limits (5 requests per 5.5 seconds) and extension limits (10 requests per second).
+
+### Resolver Intelligence
+
+Resolvers inspect the GraphQL AST to determine which MusicBrainz `inc` parameters are needed. This eliminates over-fetching and under-fetching by requesting exactly the data required for the query.
+
+## Package Distribution
+
+The NPM package exports:
+
+- Main module with `start()`, `middleware()`, `schema`, `context`
+- Built-in extensions as separate modules
+- `schema.json` for tooling and introspection
+- Binary command for CLI usage
+
+## Version Requirements
+
+| Component | Minimum Version | Notes |
+|-----------|----------------|-------|
+| Node.js | 12.18.0 | ESM support required |
+| GraphQL | 15.5.0 | Not latest (v16+ available) |
+| Express | 4.x | Via express-graphql |
+
+## Configuration Surface
+
+GraphBrainz exposes 10+ environment variables for configuration:
+
+- `MUSICBRAINZ_BASE_URL` - MusicBrainz API endpoint
+- `GRAPHBRAINZ_PATH` - GraphQL endpoint path
+- `GRAPHBRAINZ_CORS_ORIGIN` - CORS configuration
+- `GRAPHBRAINZ_CACHE_SIZE` - LRU cache size
+- `GRAPHBRAINZ_CACHE_TTL` - Cache TTL in milliseconds
+- `GRAPHBRAINZ_GRAPHIQL` - Enable GraphiQL interface
+- `GRAPHBRAINZ_EXTENSIONS` - Extension loading
+- `PORT` - Server port
+- `NODE_ENV` - Environment mode
+- Per-extension variables (API keys, cache settings)
+
+## Development Tooling
+
+| Tool | Purpose |
+|------|---------|
+| AVA | Test framework |
+| ava-nock | HTTP mocking (play/record/cache) |
+| c8 | Code coverage |
+| Travis CI | Continuous integration (Node 12/14/15) |
+| Codecov + Coveralls | Coverage reporting |
+| debug | Namespace-based logging |
+
+## Project Maturity
+
+GraphBrainz v9.0.0 represents a mature, stable project with:
+
+- Comprehensive test suite (1475+ lines)
+- Production-proven caching and rate limiting
+- Relay-compliant GraphQL implementation
+- Extensible architecture for metadata aggregation
+- 5+ years of development history
+
+The project has not seen major updates in recent years, indicating stability but potential technical debt in dependencies (Node.js 12 baseline, GraphQL v15).