feat(backend): Server-Sent Events (SSE) Live Frame Streaming Engine

[Sanan507]

Overview

Implement Server-Sent Events (SSE) streaming for simulation endpoints. For large benchmarks ($N > 1000$ or complex $100 \times 100$ grids), SSE streams simulation frames in real-time as they are computed, eliminating large memory payloads and enabling instant playback start.

Implementation Details & File Reference

• SSE Controller: Create backend/src/main/java/com/algorithmrace/visualizer/controller/StreamController.java.
  • Endpoint GET /api/simulations/stream/sorting returning SseEmitter.
• Streaming Service: Update backend algorithm models to accept a frame consumer callback Consumer<SimulationFrame>, emitting frames directly to the emitter as the loop runs.
• Frontend EventSource: Create frontend/src/services/sseClient.ts to consume EventSource streams into the usePlayback frame buffer.

Definition of Done

• SSE streaming endpoint streams simulation frames asynchronously.
• Frontend starts animating instantly without waiting for total simulation completion.
• Handles connection dropouts and emitter completion cleanly.

Skill Level

Hard — Spring SseEmitter implementation, reactive frame streaming, and client EventSource handling.