V2.1.0 rc

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+      - run: npm install
+      - run: npm run lint
+
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+      - run: npm install
+      - run: npm test

.gitignore

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+# Dependency directories
+node_modules/
+jspm_packages/
+bun.lockb
+node_modules.bun/
+
+# Deno
+.deno/
+deno.lock
+
+# Build outputs
+dist/
+build/
+.next/
+.nuxt/
+.output/
+.cache/
+out/
+
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+.pnpm-debug.log*
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+*.lcov
+
+# nyc documentation
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+jspm_packages/
+
+# TypeScript v1 declaration files
+typings/
+
+# TypeScript cache
+*.tsbuildinfo
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Optional stylelint cache
+.stylelintcache
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variable files
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+.parcel-cache
+
+# Next.js build output
+.next
+out
+
+# Nuxt.js build / generate output
+.nuxt
+dist
+
+# Gatsby files
+.cache/
+public/
+
+# vue-cli dist
+dist/
+
+# Serverless directories
+.serverless/
+
+# FuseBox cache
+.fusebox/
+
+# DynamoDB Local files
+.dynamodb/
+
+# Tern JS port file
+.tern-port
+
+# Stores VS Code state
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/code-actions.json
+
+# IntelliJ IDEA
+.idea/
+
+.crush
+.obsidian
+
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+Icon
+
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+
+# Directories potentially created by macOS
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+# Other Editors
+*.swp
+*.swo
+*~

API_REFERENCE.md

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+# API Reference
+
+This file catalogs every public export from `@git-stunts/trailer-codec` so you can confidently import, configure, and extend the codec.
+
+## Encoding & decoding helpers
+
+### `decodeMessage(message: string)`
+- Deprecated convenience wrapper around `new TrailerCodec().decode(message)`.
+- Input: a raw commit payload (title, optional body, trailers) as a string.
+- Output: `{ title: string, body: string, trailers: Record<string, string> }` where `body` is trimmed via `formatBodySegment` (see below) and trailer keys are normalized to lowercase.
+- Throws `TrailerCodecError` subclasses (e.g., `TrailerNoSeparatorError`, `TrailerValueInvalidError`, or `CommitMessageInvalidError`) for invalid titles, missing blank lines, oversized messages, or malformed trailers.
+
+### `encodeMessage({ title: string, body?: string, trailers?: Record<string, string> })`
+-- Deprecated convenience wrapper around `new TrailerCodec().encode(payload)`.
+- Builds a `GitCommitMessage` under the hood and returns the canonical string. Trailers are converted from plain objects to `GitTrailer` instances via the default factory (see `GitTrailer` below).
+
+### `formatBodySegment(body?: string, { keepTrailingNewline = false })`
+- Shared helper for `decodeMessage` to trim whitespace while optionally keeping a trailing newline when you plan to write the body back into a template.
+
+### `createMessageHelpers({ service, bodyFormatOptions } = {})`
+- Returns `{ decodeMessage, encodeMessage }` bound to the injected `TrailerCodecService` instance; a new service is created when none is provided.
+- Supports `bodyFormatOptions` (forwarded to `formatBodySegment`) and is useful for advanced/test wiring.
+
+### `createDefaultTrailerCodec({ bodyFormatOptions } = {})`
+- Creates a new `TrailerCodecService`, builds a `TrailerCodec`, and returns it so you can call `encodeMessage()`/`decodeMessage()` without manually wiring services.
+
+### `TrailerCodec`
+- Constructor opts: `{ service = new TrailerCodecService(), bodyFormatOptions }`.
+- Exposes `decodeMessage(input)`/`decode(input)` and `encodeMessage(payload)`/`encode(payload)` methods that delegate to `createMessageHelpers()`.
+- The `decode()` and `encode()` methods are convenience aliases added in v2.1.0.
+
+### `createConfiguredCodec({ keyPattern, keyMaxLength, parserOptions, formatters, bodyFormatOptions } = {})`
+- Creates a schema bundle via `createGitTrailerSchemaBundle`, a `TrailerParser`, and a `TrailerCodecService`, then exposes `{ service, helpers, decodeMessage, encodeMessage }`.
+- Use this when you need custom trailer patterns, parser tweaks, formatter hooks, or tightly controlled key lengths.
+
+## Domain model exports
+
+### `GitCommitMessage`
+```ts
+new GitCommitMessage(
+  payload: { title: string; body?: string; trailers?: GitTrailerInput[] },
+  options?: { trailerSchema?: ReturnType<typeof getDefaultTrailerSchemaBundle>['schema']; formatters?: { titleFormatter?: (value: string) => string; bodyFormatter?: (value: string) => string } }
+);
+```
+- Validates via `GitCommitMessageSchema`, normalizes title/body with optional formatters, and converts `trailers` to `GitTrailer` instances.
+- `toString()` returns a Git-style commit string (title, optional body, blank line, trailers).
+
+### `GitTrailer`
+- Accepts `(key: string, value: string, schema = GitTrailerSchema)`.
+- Validates using `GitTrailerSchema` and normalizes the key to lowercase and the value to a trimmed string.
+- Throws `TrailerInvalidError` or `TrailerValueInvalidError` when the provided key/value fail schema validation.
+
+## Services & parsers
+
+### `TrailerCodecService`
+- Core decode/encode logic; see `docs/SERVICE.md` for how the pipeline is wired.
+- Constructor options:
+  - `schemaBundle`: result of `createGitTrailerSchemaBundle({ keyPattern, keyMaxLength })` (defaults: `keyPattern` = `[A-Za-z0-9_-]+`, `keyMaxLength` = `100`, see the schema section below).
+  - `trailerFactory`: function that instantiates trailers (defaults to `GitTrailer`).
+  - `parser`: instance of `TrailerParser`.
+  - `messageNormalizer`, `titleExtractor`, `bodyComposer`: helper classes that normalize lines, extract the title, and compose the body.
+  - `formatters`: optional `{ titleFormatter, bodyFormatter }` that run before serialization.
+- `decode(message)` enforces message size, normalizes lines, extracts the title, splits body/trailers with `TrailerParser`, composes the body, builds trailers with `trailerFactory`, and constructs a `GitCommitMessage`.
+  - `encode(messageEntity)` accepts either a `GitCommitMessage` instance or a plain payload object, validates it against `GitCommitMessageSchema`, and returns the canonical commit string produced by the entity.
+
+### `TrailerParser`
+- Constructor takes `{ keyPattern = TRAILER_KEY_RAW_PATTERN_STRING }`.
+- `split(lines)` finds where the trailer block begins (walks backward, validates the blank-line separator) and returns `{ bodyLines, trailerLines }`.
+- Used internally by `TrailerCodecService` and is injectable for custom parsing strategies.
+
+## Schemas & constants
+
+### `createGitTrailerSchemaBundle({ keyPattern, keyMaxLength } = {})`
+- Returns `{ schema, keyPattern, keyRegex }` with the schema used by `GitTrailer` and `GitCommitMessage`.
+- Default `keyPattern` is `[A-Za-z0-9_-]+` and `keyMaxLength` defaults to `100`.
+
+### `TRAILER_KEY_RAW_PATTERN_STRING` / `TRAILER_KEY_REGEX`
+- Exported from the default schema bundle; use them to keep custom parsers aligned with validation rules.
+
+## Errors
+
+### `TrailerCodecError`
+- Base error type used throughout the codec (`index.js` re-exports it).
+- Signature: `(message: string, meta: Record<string, unknown> = {})`.
+
+### Validation error subclasses
+
+| Error | Thrown by | Meaning |
+| --- | --- | --- |
+| `TrailerTooLargeError` | `MessageNormalizer.guardMessageSize` (called by `TrailerCodecService.decode` and the exported `decodeMessage`) | Message exceeds the 5 MB guard in `MessageNormalizer`. |
+| `TrailerNoSeparatorError` | `TrailerParser.split` / `TrailerCodecService.decode` when the blank-line guard fails | A trailer block was found without a blank line separating it from the body (see `TrailerParser`). |
+| `TrailerValueInvalidError` | `GitTrailer` via `GitTrailerSchema.parse` when constructing trailers | A trailer value violated the `GitTrailerSchema` (e.g., contained `\n`). |
+| `TrailerInvalidError` | `GitTrailer` via `GitTrailerSchema.parse` when constructing trailers | Trailer key or value failed validation (`GitTrailerSchema`). |
+| `CommitMessageInvalidError` | `GitCommitMessage` via `GitCommitMessageSchema.parse` (triggered by `TrailerCodecService.decode` or `encode`) | The `GitCommitMessageSchema` rejected the title/body/trailers combination. |

ARCHITECTURE.md

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+# Architecture: @git-stunts/trailer-codec
+
+This project adheres to **Hexagonal Architecture** (Ports and Adapters) and **Domain-Driven Design (DDD)** principles to ensure robustness, testability, and separation of concerns.
+
+## 🧱 Core Concepts
+
+### Domain Layer (`src/domain/`)
+The core business logic, isolated from external frameworks or I/O.
+
+- **Entities**: Mutable objects with identity and lifecycle (e.g., `GitCommitMessage`).
+- **Value Objects**: Immutable objects defined by their attributes (e.g., `GitTrailer`).
+- **Services**: Domain logic that doesn't fit naturally into an entity (e.g., `TrailerCodecService` for parsing/serializing).
+- **Errors**: Domain-specific error hierarchy (`TrailerCodecError` plus concrete subclasses such as `TrailerNoSeparatorError` and `TrailerValueInvalidError`).
+- **Schemas**: Zod schemas for validation of domain objects.
+
+### Ports Layer (`src/ports/`)
+*Currently implicit.* The public API (exported via `index.js`) serves as the primary input port/facade for consumers. Since this library is primarily a data transformation tool (codec), it does not currently have complex output ports for I/O.
+
+## 📂 Directory Structure
+
+```
+src/
+├── domain/
+│   ├── entities/       # GitCommitMessage
+│   ├── errors/         # TrailerCodecError and validation subclasses
+│   ├── schemas/        # Zod schemas
+│   ├── services/       # TrailerCodecService
+│   └── value-objects/  # GitTrailer
+```
+
+## 🧪 Testing Strategy
+
+- **Unit Tests** (`test/unit/`): Comprehensive tests for entities, value objects, and services.
+- **Test Doubles**: The architecture supports easy mocking of dependencies if the system grows.
+
+## 🛠️ Design Decisions
+
+1.  **Zod for Validation**: We use Zod for runtime schema validation but wrap it in domain-specific `TrailerCodecError` subclasses to avoid leaking implementation details.
+2.  **Case Normalization**: Git trailer keys are case-insensitive. We normalize them to lowercase in the `GitTrailer` Value Object to ensure consistency.
+3.  **Facade Pattern**: `index.js` acts as a facade, providing a simple, backward-compatible API while exposing the rich domain model for advanced users.