feat: forward id, streaming start, streaming end of content blocks

[lgrammel]

Background

When streaming, it was not possible to distinguish different content of the same type (e.g. 2 text content parts) sent from Anthropic and OpenAI APIs. This prevents building UIs where e.g. multiple reasoning blocks stream at the same time, or where a text part is followed by sources and then by further text parts.

Summary

• text and reasoning parts have ids, and start/delta/end events when streaming

Verification

Source streaming with anthropic server side tool call in UI.

Tasks

• change spec
• streamText
• streamObject
• smooth stream transformation
• extract reasoning middleware
• simulate streaming middleware
• ui message stream parts text
• ui message stream parts reasoning
• ui message streaming
• anthropic provider
• openai responses provider
• openai chat provider
• openai completion provider
• perplexity provider
• cohere provider
• openai compatible chat provider
• groq provider
• openai compatible completion provider
• xai provider
• mistral provider
• bedrock provider
• google provider
• langchain
• llamaindex
• ui test updates react
• ui test updates vue
• ui test updates svelte
• rsc
• examples fixes

Future Work

• add state field to ui message reasoning and text parts