feat(generator-asyncapi): add attachHeadersToSchema option

[boyney123]

What This PR Does

Adds a new attachHeadersToSchema boolean option to the AsyncAPI generator that combines message headers and payload into a single unified schema. When enabled, the generated schema wraps the original payload and headers under properties.payload and properties.headers respectively. This is useful for consumers who need header metadata alongside the message body.

Changes Overview

Key Changes

• Add attachHeadersToSchema option to the options schema and destructuring
• Extract schema retrieval into getSchemaForMessage helper that conditionally merges headers
• Add getSchemaFromMessagePart helper to normalize nested schema formats
• Add isJSONSchemaMessage guard to skip header attachment for non-JSON schemas (e.g., Avro)
• Add three test cases covering: headers + payload merge, no-headers fallback, and non-JSON schema skip
• Add Avro + headers test fixture file

How It Works

When attachHeadersToSchema is true, the generator checks if the message has headers and uses a JSON schema format. If both conditions are met, it wraps the payload and headers into a combined { type: "object", properties: { headers, payload } } schema. For non-JSON schema formats (like Avro) or messages without headers, the original payload schema is returned unchanged.

Breaking Changes

None. The option defaults to false, so existing behavior is preserved.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: a0ba207

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@eventcatalog/generator-asyncapi	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR