Migrate genui (Flutter SDK) to A2UI protocol v1.0

[sethgw]

Description

The Flutter GenUI SDK (flutter/genui) currently implements A2UI protocol v0.9/v0.9.1. The v1.0 specification is now published (evolution guide, v1.0 spec + schemas), and the SDK should be migrated to it.

Scope (per the evolution guide):

• version: "v1.0" envelopes and capabilities/data-model namespaces
• createSurface: theme → surfaceProperties, inline components/dataModel
• Bidirectional RPC: callFunction/functionResponse with callableFrom runtime boundary checks (INVALID_FUNCTION_CALL), and actionResponse correlated by actionId/wantResponse
• Explicit-null deletion in updateDataModel (also resolves UpdateDataModel doesn't distinguish between the value-omitted and value-null cases #1896)
• Catalog changes: functions as a map with static returnType/callableFrom, $defs/surfaceProperties, optional instructions, UAX Initial commit for a2ui_restaurant_finder and a generic a2UI extension. #31 entity naming
• Basic catalog: TextField.placeholder, Slider.steps, Video.posterUrl
• @index system function in template loops; @ prefix reserved
• A2A extension URI a2ui/v1.0 and application/a2ui+json MIME type

Implementation

PR: flutter/genui#996

🤖 Generated with Claude Code