fix(agent-routes): return Vercel SSE Data Stream for agent chat

[Copilot]

Agent chat (/api/v1/ai/agents/:agentName/chat) returned plain JSON while the Studio frontend expects Vercel AI SDK v6 UI Message Stream Protocol (SSE). Result: API responds correctly, but DefaultChatTransport can't parse the response and the chat panel renders nothing.

Backend — agent-routes.ts

• Default to SSE streaming (stream !== false), matching the general chat route
• Uses streamChatWithTools() + encodeVercelDataStream() — same codepath as /api/v1/ai/chat
• JSON fallback only when stream: false is explicitly set

// Before: always JSON
const result = await aiService.chatWithTools(fullMessages, opts);
return { status: 200, body: result };

// After: SSE by default, JSON opt-in
const wantStream = body.stream !== false;
if (wantStream) {
  const events = aiService.streamChatWithTools(fullMessages, opts);
  return {
    status: 200, stream: true, vercelDataStream: true,
    events: encodeVercelDataStream(events),
  };
}

Frontend — AiChatPanel.tsx

• Enhanced error UI: shows ShieldAlert icon with structured message instead of a flat string
• Detects SSE/parse-related errors and surfaces a contextual hint about expected wire format

Tests

• 3 new tests: default SSE mode, explicit stream: true, stream: false JSON fallback
• Existing agent route tests updated to pass stream: false where they assert on resp.body
• All 282 tests pass

[vercel]

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Project	Deployment	Actions	Updated (UTC)
objectstack-play	Ready	Preview, Comment	Apr 8, 2026 6:53am
spec	Ready	Preview, Comment	Apr 8, 2026 6:53am

[Copilot]

Pull request overview

This PR fixes the agent-specific chat route (/api/v1/ai/agents/:agentName/chat) so it returns a Vercel AI SDK v6-compatible streaming response by default (instead of always returning JSON), matching what the Studio chat UI transport expects.

Changes:

• Update agent chat route to default to streaming (stream !== false) and use streamChatWithTools() + encodeVercelDataStream(), with JSON fallback when stream: false.
• Update/extend route tests to cover default streaming, explicit streaming, and explicit JSON fallback.
• Improve Studio chat panel error UI messaging for stream/parse-related failures, and document the fix in the changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/services/service-ai/src/routes/agent-routes.ts	Switch agent chat endpoint to streaming-by-default and encode stream in Vercel-compatible format, with JSON fallback.
packages/services/service-ai/src/__tests__/chatbot-features.test.ts	Update existing assertions to use stream: false where JSON is expected; add new streaming behavior tests.
apps/studio/src/components/AiChatPanel.tsx	Improve error rendering and add a hint for SSE/stream parsing failures.
CHANGELOG.md	Document the agent chat streaming fix and related Studio UI behavior improvement.

[Copilot]

The streaming response is returning contentType and headers, but RouteResponse (from routes/ai-routes.ts) doesn’t define those fields and the runtime HttpDispatcher.handleAI() streaming path ignores route-provided headers/contentType entirely (it constructs its own headers from vercelDataStream). Either remove these fields here to avoid dead/misleading data, or extend RouteResponse + update HttpDispatcher.handleAI() to propagate streaming headers (e.g., the x-vercel-ai-ui-message-stream header) when present.

[Copilot]

The endpoint comments/description call this the “Vercel Data Stream Protocol (SSE)”, but the encoder being used (stream/vercel-stream-encoder.ts) explicitly implements the Vercel AI SDK v6 UI Message Stream Protocol (SSE data: frames with JSON payloads). Please align the wording here (and/or naming like vercelDataStream) to the actual wire protocol to avoid confusion when debugging transports.