Research plan for streaming custom data alongside AI responses

[Copilot]

User requested a plan with multiple approaches to add an ability for additional data to be streamed alongside streaming responses, similar to AI SDK's streaming custom data feature.

Created comprehensive technical analysis with four distinct approaches:

Approach 1: Extended Delta Format (Recommended)

• Extend existing StreamDelta to include optional data field for arbitrary JSON
• Reuses current delta infrastructure (throttling, compression, subscriptions)
• Minimal changes, no breaking API updates

Approach 2: Parallel Metadata Stream

• Separate streamMetadata table running parallel to streamDeltas
• Independent cursor/subscription mechanism
• Complete separation of concerns, different streaming rates possible

Approach 3: Callback-Based Side Channel

• Add onStreamData callback to streamText/generateText options
• Developer-controlled timing and content
• Writes to separate table/structure

Approach 4: Enhanced onStepFinish with Data Attachment

• Extend existing onStepFinish to return custom data
• Auto-attached to step/message metadata
• Natural extension of current patterns

Recommendation: Approach 1 as primary (best fit with existing architecture, proven infrastructure, simple API) with Approach 4 as complementary for step-level metadata.

Implementation sketch:

// In DeltaStreamer
await streamer.addParts(parts, { 
  customData: { progress: 0.5, currentTool: "search" } 
});

// Extended delta format
interface StreamDelta {
  streamId: string;
  start: number;
  end: number;
  parts: T[];
  data?: Record<string, JSONValue>; // New
}

No code changes made - this PR documents the research and recommendation for review before implementation.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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• ai-sdk.dev
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npm i https://pkg.pr.new/zboyles/agent/@convex-dev/agent@9

commit: 502d9d8