feat: add training resource limits (500MB size check + 30-min timeout)

- Import concurrent.futures for timeout support
- In _run_training_background: check df.memory_usage(deep=True).sum()
  after loading the labeled dataset; raise ValueError if > 500MB
- Wrap model.fit() in a ThreadPoolExecutor with a 1800s timeout;
  on TimeoutError update DB status to "failed" with message
  "Training timed out after 30 minutes" and return early
- Mark task 5.7 as done in openspec/changes/code-review-fix/tasks.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/ml/app/main.py

@@ -4,6 +4,7 @@ FastAPI inference service for candlestick pattern prediction.
 Provides REST API endpoints for model serving, health checks, and prediction.
 """
 
+import concurrent.futures
 import hashlib
 import logging
 import os
@@ -1166,6 +1167,18 @@ def _run_training_background(run_id: str, model_type: str, config: PipelineConfi
         if "label" not in df.columns:
             raise ValueError("Labeled dataset must have 'label' column")
 
+        # Check dataset size: reject if it exceeds 500MB in memory
+        _DATASET_SIZE_LIMIT_BYTES = 500 * 1024 * 1024  # 500 MB
+        dataset_size_bytes = df.memory_usage(deep=True).sum()
+        if dataset_size_bytes > _DATASET_SIZE_LIMIT_BYTES:
+            raise ValueError(
+                f"Dataset too large. Maximum size is 500MB "
+                f"(current size: {dataset_size_bytes / (1024 * 1024):.1f}MB)."
+            )
+        logger.info(
+            f"Dataset size check passed: {dataset_size_bytes / (1024 * 1024):.1f}MB"
+        )
+
         feature_cols = [
             col for col in df.columns
             if col not in ("label", "time", "timestamp")
@@ -1183,11 +1196,45 @@ def _run_training_background(run_id: str, model_type: str, config: PipelineConfi
             X, y, training_cfg.test_split, training_cfg.validation_split
         )
 
-        # Train model
-        model_instance = create_model(
-            model_type, training_cfg.hyperparameters, training_cfg.class_weights
-        )
-        model_instance.fit(X_train, y_train)
+        # Run model training with a 30-minute timeout
+        _TRAINING_TIMEOUT_SECONDS = 1800  # 30 minutes
+
+        def _do_train():
+            _model = create_model(
+                model_type, training_cfg.hyperparameters, training_cfg.class_weights
+            )
+            _model.fit(X_train, y_train)
+            return _model
+
+        with concurrent.futures.ThreadPoolExecutor(max_workers=1) as executor:
+            future = executor.submit(_do_train)
+            try:
+                model_instance = future.result(timeout=_TRAINING_TIMEOUT_SECONDS)
+            except concurrent.futures.TimeoutError:
+                logger.error(
+                    f"Training timed out after 30 minutes: run_id={run_id}"
+                )
+                try:
+                    with get_db() as db:
+                        stmt = (
+                            sa_update(TrainingRun)
+                            .where(TrainingRun.run_id == run_id)
+                            .values(
+                                status="failed",
+                                completed_at=datetime.utcnow(),
+                                metrics_summary={
+                                    "error": "Training timed out after 30 minutes"
+                                },
+                            )
+                        )
+                        db.execute(stmt)
+                        db.commit()
+                except Exception as db_exc:
+                    logger.error(
+                        f"Failed to update DB for timed-out run {run_id}: {db_exc}"
+                    )
+                return
+
         logger.info("Model training complete")
 
         # Evaluate