Tracer Bullet: Project-Scoped Chat with TanStack AI + Durable Streams

[imharrisonking]

Goal

Validate a project-scoped chat route using TanStack AI with SolidType-style durable stream output, rendered live in the client.

Minimal Scope

• Implement /app/projects/:projectId/chat route.
• Add pathless _chat.tsx layout containing the chat input/composer.
• Add chat.tsx child route rendering streamed assistant output.
• Add POST /api/chat/run endpoint using TanStack AI for model streaming.
• Write stream chunks to durable stream using the SolidType event schema.
• Subscribe client UI to durable stream and render incoming chunks.
• Happy path only; defer edge/error handling and polish.

Acceptance Criteria

• User can send a message from /app/projects/:projectId/chat and receive a streamed assistant response.
• Durable stream output is visible in the client and drives rendered chat updates.
• Chat input lives in _chat.tsx pathless layout, not per-child route.
• Document implementation learnings and constraints for follow-on phases.

Related Feature

Unlocks: persistence, multi-session UX, workspace-wide chat index.

Additional Context

• Use SolidType durable stream event conventions (content, tool_call, tool_result, done, error).
• Workspace context will come from user.workspaceId in follow-up phases.