Problem

Current training progress events are emitted as loosely structured payloads (message + numeric test index), and the frontend stores them by array index.

This makes the contract fragile and hard to extend:

• UI behavior depends on parsing free-form strings like "Starting" / "Finish"
• No stable run_id in event payload to scope updates
• No explicit epoch/batch/metric fields for charting
• Hard to support multi-run comparison and robust progress visualizations

Why this matters

A stable telemetry contract is required for:

• real-time training charts
• run comparison dashboard
• reliable retry/reconnect handling
• future tuning/interpretability workflows

String-based progress messages are hard to validate and can silently break UI.

Current behavior (observed)

• Backend emits generic message events from CustomProgressBar
• Frontend in Training.jsx maps updates using resultValues[parseInt(resp.test)]
• Progress state is not strongly typed and not run-scoped

Proposed solution

Introduce versioned structured events for training:

• training_started
• training_update
• training_complete
• training_error

Each event should include a typed payload, e.g.:

{
  "run_id": "<uuid-or-id>",
  "phase": "train|eval",
  "epoch": 3,
  "batch": 12,
  "steps": 100,
  "metrics": {
    "loss": 0.42,
    "accuracy": 0.88,
    "val_loss": 0.50,
    "val_accuracy": 0.84
  },
  "message": "optional human-readable message",
  "timestamp": "ISO-8601"
}