sendDataModel sync + catalog & theme support

[23min]

Spec reference

• A2UI v0.9 Evolution Guide

Current behavior

• We parse sendDataModel from createSurface but do not echo the data model back in client-to-server messages.
• We do not parse catalogId from createSurface.
• We do not parse or apply theme properties.

Required behavior

sendDataModel sync: When sendDataModel: true is set on createSurface, the client must include the full data model in the A2A message metadata when sending actions back to the server.

Catalog ID: The createSurface message includes a catalogId field specifying which component catalog the server chose. The renderer should parse and store this value.

Theme support: The createSurface message can include theme parameters (e.g., primaryColor). The renderer should apply these to component styling.

Affected files

• src/A2UI.Blazor/Services/A2UIStreamClient.cs — include data model in action metadata
• src/A2UI.Blazor/Services/SurfaceManager.cs — parse catalogId and theme
• src/A2UI.Blazor/Components/ — apply theme properties to rendered components

SPECIFICATION.md reference

• Client-to-Server Communication: sendDataModel sync row
• Protocol Features: Catalog ID in createSurface row
• Protocol Features: Theme support row

Acceptance criteria

• Implementation matches spec
• Tests added (red-green-refactor)
• SPECIFICATION.md updated (gap → compliant)
• Sample servers updated if affected (parity)
• Sample apps updated if affected (parity)

[23min]

Completed in PR #18