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Evolution Guide v0.9 → v0.9.1

This guide is automatically included from specification/v0_9_1/docs/evolution_guide.md. Any updates will automatically appear here.

For more information, see the following related documentation:

A2UI Protocol Evolution Guide: v0.9 to v0.9.1

This document describes the changes between A2UI version 0.9 and version 0.9.1. For changes from version 0.8 to 0.9, please refer to the v0.9 Evolution Guide.

1. Executive Summary

Version 0.9.1 is a minor refinement of the v0.9 specification. The key changes are:

  1. MIME Type Standardization: Standardized all references to the A2UI message payload MIME type to application/a2ui+json (replacing the legacy application/json+a2ui).
  2. Surface ID Uniqueness Relaxation: Relaxed the requirement for surfaceId to be globally unique for the renderer's lifetime. It must still be unique among currently active surfaces, and it remains an error to call createSurface on an existing surface without first deleting it, but the explicit lifetime uniqueness constraint is removed.

2. Detailed Changes

2.1. MIME Type Standardization

In previous draft iterations of the v0.9 extension specification, the legacy application/json+a2ui MIME type was referenced. Version 0.9.1 standardizes all specification guides and extension metadata examples to use application/a2ui+json.

2.2. Surface ID Requirements

In a2ui_protocol.md, the definition and requirements for surfaceId were updated:

  • The restriction that surfaceId "must be globally unique for the renderer's lifetime" is removed.
  • Instead, the uniqueness constraint is limited to active surfaces: it remains an error to send createSurface for a surfaceId that already exists without first deleting it.

3. Migration Guide

Since v0.9.1 is fully compatible with v0.9 payloads (the version fields in schemas accept both "v0.9" and "v0.9.1"), clients and servers can upgrade seamlessly.

  • Action for Implementers: Update any hardcoded MIME type references from application/json+a2ui to application/a2ui+json.