chore: Add CLAUDE.md (#113)

Signed-off-by: Daniel Azuma <dazuma@gmail.com>

Author: dazuma

.rubocop.yml

@@ -140,6 +140,7 @@ Metrics/AbcSize:
 Metrics/BlockLength:
   Exclude:
     - "test/**/test_*.rb"
+    - "cloud_events.gemspec"
 Metrics/ClassLength:
   Max: 300
 Metrics/CollectionLiteralLength:

CLAUDE.md

@@ -0,0 +1,82 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Ruby SDK for the [CloudEvents](https://cloudevents.io/) specification (CNCF). Gem name: `cloud_events`. Supports CloudEvents spec versions 0.3 and 1.0. Zero runtime dependencies; Ruby 2.7+.
+
+## Development Commands
+
+This project uses [Toys](https://github.com/dazuma/toys) as the task runner (not Rake).
+
+```bash
+bundle install              # Install dependencies
+gem install toys            # Install task runner (required)
+
+toys test                   # Run minitest unit tests
+toys cucumber               # Run Cucumber conformance tests
+toys rubocop                # Run linter
+toys yardoc                 # Generate YARD documentation
+toys build                  # Build .gem file into pkg/
+toys install                # Build and install gem locally
+toys ci                     # Run full CI suite (test + cucumber + rubocop + yard + build)
+toys ci --only --test       # Run only minitest
+toys ci --only --cucumber   # Run only Cucumber tests
+toys ci --only --rubocop    # Run only linter
+```
+
+To focus a single test, add `focus` before a test method (requires `minitest-focus` gem from the bundle).
+
+## Code Style
+
+Enforced by Rubocop (`.rubocop.yml`):
+- Double-quoted strings
+- Trailing commas in multiline arrays/hashes
+- 120 character line limit
+- `[:symbol]` array style (not `%i`)
+- `["word"]` array style (not `%w`)
+- All source files require `# frozen_string_literal: true`
+
+## Architecture
+
+### Event Model
+
+`CloudEvents::Event` is both a module (included by all event classes) and a factory via `Event.create(spec_version:, **attrs)`.
+
+- **`Event::V1`** — CloudEvents 1.0 (primary). Immutable (frozen), Ractor-shareable on Ruby 3+.
+- **`Event::V0`** — CloudEvents 0.3 (legacy).
+- **`Event::Opaque`** — Wrapper for events that couldn't be fully decoded.
+
+V1 has a dual data model: `data` holds the decoded Ruby object, `data_encoded` holds the serialized string/bytes. Formatters use `data_encoded` if present, otherwise encode `data`.
+
+### HTTP Binding (`HttpBinding`)
+
+Handles encoding/decoding CloudEvents to/from HTTP (Rack env hashes). Supports:
+- **Binary content mode** — event attributes as `CE-*` headers, data in body
+- **Structured content mode** — entire event serialized in body (e.g., JSON)
+- **Batch mode** — array of events in body
+
+`HttpBinding.default` returns a singleton with `JsonFormat` and `TextFormat` pre-registered. Custom formatters are registered via `register_formatter`.
+
+### Format Layer
+
+- **`JsonFormat`** — Encodes/decodes `application/cloudevents+json` and batch format. Also handles JSON data encoding/decoding for binary mode.
+- **`TextFormat`** — Handles `text/*` data.
+- **`Format::Multi`** — Composite that tries multiple formatters in registration order.
+
+Formatters implement up to four methods: `decode_event`, `encode_event`, `decode_data`, `encode_data`. Return `nil` to decline handling (next formatter is tried).
+
+### Content-Type Parser (`ContentType`)
+
+RFC 2045 compliant parser. Handles charset defaults: `text/plain` defaults to `us-ascii`, other `text/*` and JSON types default to `utf-8`.
+
+### Error Hierarchy
+
+All errors inherit from `CloudEventsError`: `NotCloudEventError`, `UnsupportedFormatError`, `FormatSyntaxError`, `SpecVersionError`, `AttributeError`.
+
+## Contributing
+
+- Conventional Commits format required (`fix:`, `feat:`, `docs:`, etc.)
+- Commits must be signed off (`git commit --signoff`)
+- Run `toys ci` before submitting PRs

cloud_events.gemspec

@@ -17,7 +17,16 @@ version = ::CloudEvents::VERSION
     "and unmarshalling event data."
   spec.homepage = "https://github.com/cloudevents/sdk-ruby"
 
-  spec.files = ::Dir.glob("lib/**/*.rb") + ::Dir.glob("*.md") + [".yardopts"]
+  spec.files = ::Dir.glob("lib/**/*.rb") +
+               [
+                 ".yardopts",
+                 "CHANGELOG.md",
+                 "CONTRIBUTING.md",
+                 "MAINTAINERS.md",
+                 "README.md",
+                 "RELEASING.md",
+                 "LICENSE",
+               ]
   spec.require_paths = ["lib"]
   spec.required_ruby_version = ">= 2.7"