refactor(gql): migrate to IR-based code generation architecture (#73)

## Summary

- Replace 4 individual language generator scripts with unified IR-based
plugin system
- Single GraphQL schema parsing instead of 5 separate parsers
- Generated output is 100% identical to previous scripts

## Architecture

```
GraphQL Schema (src/*.graphql)
         ↓
    [1] Parser (codegen/core/parser.ts)
         ↓
    [2] Transformer → IR (codegen/core/transformer.ts)
         ↓
    [3] Language Plugins (codegen/plugins/*.ts)
         ↓
    Generated Files (src/generated/*)
```

## Changes

### New Plugin System (`codegen/plugins/`)
| Plugin | Features |
|--------|----------|
| **swift.ts** | Codable protocol, ErrorCode custom init, platform
defaults |
| **kotlin.ts** | Sealed interface, fromJson/toJson, nullable patterns |
| **dart.ts** | Sealed class, factory constructors, extends/implements |
| **gdscript.ts** | _init() pattern, from_json/to_json, Variant type |

### Deleted Scripts (3,687 lines removed)
- `generate-swift-types.mjs` (831 lines)
- `generate-kotlin-types.mjs` (939 lines)
- `generate-dart-types.mjs` (1,105 lines)
- `generate-gdscript-types.mjs` (812 lines)

### Documentation Updates
- `CONTRIBUTING.md` - Added IR architecture documentation
- `CLAUDE.md` - Added code generation system section
- `packages/gql/CONVENTION.md` - Added code generation architecture
section
- `knowledge/internal/04-platform-packages.md` - Comprehensive GQL
section

## Test plan

- [x] `bun run generate` completes successfully
- [x] Generated Swift types match previous output (byte-identical)
- [x] Generated Kotlin types match previous output (byte-identical)
- [x] Generated Dart types match previous output (byte-identical)
- [x] Generated GDScript types match previous output (byte-identical)
- [x] Types synced to `packages/apple` and `packages/google`

🤖 Generated with [Claude Code](https://claude.ai/code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Centralized IR-based GraphQL code generation with language plugins
producing Swift, Kotlin, Dart, and GDScript outputs and a CLI to
generate per-language artifacts.

* **Documentation**
* Extensive guides added: codegen architecture, IR types, plugin model,
templates, and updated regeneration instructions.

* **Chores**
* Replaced legacy per-language generator scripts with the new
centralized generator; added template tooling dependency and updated
generate scripts.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: hyochan

.claude/commands/review-pr.md

@@ -31,11 +31,30 @@ When reviewing, check these project-specific rules:
 
 See [CLAUDE.md](../../CLAUDE.md) and [knowledge/internal/](../../knowledge/internal/) for full conventions.
 
-## Reply Format Rules
+## Reply Format Rules (CRITICAL)
 
 When replying to PR comments:
 
-- **Commit hash references**: Write commit hashes as plain text, NOT in code blocks
-  - CORRECT: `Fixed in f3b5fec.`
-  - WRONG: `Fixed in \`f3b5fec\`.`
-  - This ensures GitHub auto-links the commit hash to the actual commit
+### Commit Hash Formatting
+
+**NEVER wrap commit hashes in backticks or code blocks.** GitHub only auto-links plain text commit hashes.
+
+| Format | Example | Result |
+|--------|---------|--------|
+| ✅ CORRECT | `Fixed in f3b5fec.` | Clickable link to commit |
+| ❌ WRONG | `Fixed in \`f3b5fec\`.` | Plain text, no link |
+
+**Examples of correct replies:**
+
+```text
+Fixed in f3b5fec.
+
+**Changes:**
+- Updated header to use bun run generate
+```
+
+```text
+Fixed in abc1234 along with other review items.
+```
+
+**Do NOT use backticks around the commit hash** - this breaks GitHub's auto-linking feature.

.claude/commands/sync-godot-iap.md

@@ -76,9 +76,10 @@ Synchronize OpenIAP changes to the [godot-iap](https://github.com/hyochan/godot-
 
 ## Type Generation Source
 
-**OpenIAP has a built-in GDScript type generator:**
+**OpenIAP has a built-in GDScript type generator (IR-based):**
 
-- **Generator:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/scripts/generate-gdscript-types.mjs`
+- **Generator:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/codegen/plugins/gdscript.ts`
+- **Entry Point:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/codegen/index.ts`
 - **Output:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/src/generated/types.gd`
 
 ---
@@ -713,6 +714,7 @@ Now update `docs/docs/` with new API documentation for the new version.
 
 ## References
 
-- **OpenIAP GDScript Generator:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/scripts/generate-gdscript-types.mjs`
+- **OpenIAP GDScript Generator:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/codegen/plugins/gdscript.ts`
+- **OpenIAP Codegen Entry:** `/Users/crossplatformkorea/Github/hyodotdev/openiap/packages/gql/codegen/index.ts`
 - **OpenIAP Docs:** https://openiap.dev/docs
 - **Godot IAP Docs:** Check README.md

CLAUDE.md

@@ -54,9 +54,30 @@ openiap/
 
 - `packages/apple/Sources/Models/Types.swift`
 - `packages/google/openiap/src/main/Types.kt`
+- `packages/gql/src/generated/*` - All generated type files
 - `openiap-versions.json` - Managed by CI/CD workflows only
 
-Regenerate types with: `./scripts/generate-types.sh`
+Regenerate types: `cd packages/gql && bun run generate`
+
+### GQL Code Generation System
+
+The type generation uses an **IR-based (Intermediate Representation)** architecture:
+
+```text
+GraphQL Schema → Parser → IR → Language Plugins → Generated Code
+                              ↓
+         codegen/core/     codegen/plugins/
+         ├── types.ts      ├── swift.ts
+         ├── parser.ts     ├── kotlin.ts
+         └── transformer.ts├── dart.ts
+                           └── gdscript.ts
+```
+
+**Language plugins handle:**
+- **Swift**: Codable protocol, ErrorCode custom initializer, platform defaults
+- **Kotlin**: sealed interface, fromJson/toJson with nullable patterns
+- **Dart**: sealed class, factory constructors, extends/implements
+- **GDScript**: _init() pattern, Variant type for unions
 
 ### Git Commit Format
 

CONTRIBUTING.md

@@ -42,7 +42,7 @@ bun install
 
 ### `@hyodotdev/openiap-gql`
 
-GraphQL schema and type generation for all platforms.
+GraphQL schema and **IR-based type generation** for all platforms.
 
 ```bash
 cd packages/gql
@@ -51,12 +51,20 @@ cd packages/gql
 bun run generate
 
 # Generate for specific platform
-bun run generate:ts      # TypeScript
-bun run generate:swift   # Swift
-bun run generate:kotlin  # Kotlin
-bun run generate:dart    # Dart
+bun run generate:ts       # TypeScript (graphql-codegen)
+bun run generate:swift    # Swift (IR-based plugin)
+bun run generate:kotlin   # Kotlin (IR-based plugin)
+bun run generate:dart     # Dart (IR-based plugin)
+bun run generate:gdscript # GDScript (IR-based plugin)
 ```
 
+**Architecture:**
+```text
+GraphQL Schema → Parser → IR (Intermediate Representation) → Language Plugins → Generated Code
+```
+
+See [Code Generation Architecture](#code-generation-architecture) for details.
+
 ### `@hyodotdev/openiap-docs`
 
 Documentation website at [openiap.dev](https://openiap.dev)
@@ -275,23 +283,83 @@ Each package has its own scripts. See individual `package.json` files for detail
 ```text
 GraphQL Schema (packages/gql/src/*.graphql)
            ↓
-    Type Generation (bun run generate)
+    [1] Parser (codegen/core/parser.ts)
+           ↓
+    [2] Transformer → IR (codegen/core/transformer.ts)
+           ↓
+    [3] Language Plugins (codegen/plugins/*.ts)
+           ↓
+    ├─→ TypeScript (src/generated/types.ts)    [graphql-codegen]
+    ├─→ Swift (src/generated/Types.swift)      [IR plugin]
+    ├─→ Kotlin (src/generated/Types.kt)        [IR plugin]
+    ├─→ Dart (src/generated/types.dart)        [IR plugin]
+    └─→ GDScript (src/generated/types.gd)      [IR plugin]
+           ↓
+    Auto Sync (bun run sync)
            ↓
-    ├─→ TypeScript (src/generated/types.ts)
-    ├─→ Swift (src/generated/Types.swift) ──┐
-    ├─→ Kotlin (src/generated/Types.kt) ──┐ │
-    └─→ Dart (src/generated/types.dart)   │ │
-                                          │ │
-                 Auto Sync ───────────────┘ │
-                                            │
-    ┌───────────────────────────────────────┘
-    ↓
     ├─→ packages/apple/Sources/Models/Types.swift
-    └─→ packages/google/.../openiap/Types.kt (+ post-processing)
+    └─→ packages/google/.../openiap/Types.kt
 ```
 
 **Key Feature:** One `generate` command updates all platforms automatically!
 
+## 🏗️ Code Generation Architecture
+
+The GQL package uses an **IR-based (Intermediate Representation) code generation system**:
+
+### Directory Structure
+
+```text
+packages/gql/codegen/
+├── index.ts              # Main entry point
+├── core/
+│   ├── types.ts          # IR type definitions (IREnum, IRObject, etc.)
+│   ├── parser.ts         # GraphQL schema parser
+│   ├── transformer.ts    # AST → IR transformer
+│   └── utils.ts          # Case conversion, keyword escaping
+└── plugins/
+    ├── base-plugin.ts    # Abstract base class
+    ├── swift.ts          # Swift: Codable, ErrorCode handling
+    ├── kotlin.ts         # Kotlin: sealed interface, fromJson/toJson
+    ├── dart.ts           # Dart: sealed class, factory constructors
+    └── gdscript.ts       # GDScript: Godot engine types
+```
+
+### IR Types
+
+| IR Type | Description |
+|---------|-------------|
+| `IREnum` | Enum with values, raw values (kebab-case), legacy aliases |
+| `IRInterface` | Protocol/Interface with typed fields |
+| `IRObject` | Struct/Class with fields, implements, union membership |
+| `IRInput` | Input type with required field tracking |
+| `IRUnion` | Union with members, nested union support |
+| `IROperation` | Query/Mutation/Subscription definitions |
+
+### Language Plugin Features
+
+| Plugin | Key Features |
+|--------|--------------|
+| **Swift** | Codable protocol, ErrorCode custom init, platform defaults (ProductIOS) |
+| **Kotlin** | sealed interface, fromJson/toJson, nullable patterns, type casting |
+| **Dart** | extends/implements, factory constructors, sealed class, @override |
+| **GDScript** | _init() pattern, from_json/to_json, Variant for unions |
+
+### Schema Markers
+
+Special comments in GraphQL SDL:
+
+```graphql
+# => Union
+type RequestPurchaseResult {
+  purchase: Purchase    # Generates union variant
+  purchases: [Purchase!]
+}
+
+# Future
+fetchProducts(...): FetchProductsResult  # Wraps in Promise/async
+```
+
 ## 🔄 Common Workflows
 
 ### Adding a New Feature