Fix CNN v2 training: always save final checkpoint, derive num_layers

- Always save final checkpoint after training completes
- Derive num_layers from kernel_sizes list when multiple values provided
- Add checkpoint validation in training pipeline script
- Quote shell variables when passing args to Python

Fixes issue where no checkpoint saved when epochs < checkpoint_every.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

2 files changed, 33 insertions, 6 deletions

diff --git a/scripts/train_cnn_v2_full.sh b/scripts/train_cnn_v2_full.sh
index c98ff2d..1c683c2 100755
--- a/scripts/train_cnn_v2_full.sh
+++ b/scripts/train_cnn_v2_full.sh
@@ -300,13 +300,13 @@ python3 training/train_cnn_v2.py \
   --input "$INPUT_DIR" \
   --target "$TARGET_DIR" \
   $TRAINING_MODE_ARGS \
-  --kernel-sizes $KERNEL_SIZES \
-  --num-layers $NUM_LAYERS \
-  --mip-level $MIP_LEVEL \
-  --epochs $EPOCHS \
-  --batch-size $BATCH_SIZE \
+  --kernel-sizes "$KERNEL_SIZES" \
+  --num-layers "$NUM_LAYERS" \
+  --mip-level "$MIP_LEVEL" \
+  --epochs "$EPOCHS" \
+  --batch-size "$BATCH_SIZE" \
   --checkpoint-dir "$CHECKPOINT_DIR" \
-  --checkpoint-every $CHECKPOINT_EVERY \
+  --checkpoint-every "$CHECKPOINT_EVERY" \
   $([ "$GRAYSCALE_LOSS" = true ] && echo "--grayscale-loss")
 
 if [ $? -ne 0 ]; then
@@ -326,6 +326,11 @@ if [ ! -f "$FINAL_CHECKPOINT" ]; then
     FINAL_CHECKPOINT=$(find_latest_checkpoint)
 fi
 
+if [ -z "$FINAL_CHECKPOINT" ] || [ ! -f "$FINAL_CHECKPOINT" ]; then
+    echo "Error: No checkpoint found in $CHECKPOINT_DIR"
+    exit 1
+fi
+
 echo "[2/4] Exporting final checkpoint to binary weights..."
 echo "Checkpoint: $FINAL_CHECKPOINT"
 export_weights "$FINAL_CHECKPOINT" "$OUTPUT_WEIGHTS" || {
diff --git a/training/train_cnn_v2.py b/training/train_cnn_v2.py
index 134a5ae..d80e3a5 100755
--- a/training/train_cnn_v2.py
+++ b/training/train_cnn_v2.py
@@ -329,6 +329,9 @@ def train(args):
     kernel_sizes = [int(k) for k in args.kernel_sizes.split(',')]
     if len(kernel_sizes) == 1:
         kernel_sizes = kernel_sizes * args.num_layers
+    else:
+        # When multiple kernel sizes provided, derive num_layers from list length
+        args.num_layers = len(kernel_sizes)
 
     # Create model
     model = CNNv2(kernel_sizes=kernel_sizes, num_layers=args.num_layers).to(device)
@@ -397,6 +400,25 @@ def train(args):
             }, checkpoint_path)
             print(f"  → Saved checkpoint: {checkpoint_path}")
 
+    # Always save final checkpoint
+    print()  # Newline after training
+    final_checkpoint = Path(args.checkpoint_dir) / f"checkpoint_epoch_{args.epochs}.pth"
+    final_checkpoint.parent.mkdir(parents=True, exist_ok=True)
+    torch.save({
+            'epoch': args.epochs,
+            'model_state_dict': model.state_dict(),
+            'optimizer_state_dict': optimizer.state_dict(),
+            'loss': avg_loss,
+            'config': {
+                'kernel_sizes': kernel_sizes,
+                'num_layers': args.num_layers,
+                'mip_level': args.mip_level,
+                'grayscale_loss': args.grayscale_loss,
+                'features': ['p0', 'p1', 'p2', 'p3', 'uv.x', 'uv.y', 'sin20_y', 'bias']
+            }
+    }, final_checkpoint)
+    print(f"  → Saved final checkpoint: {final_checkpoint}")
+
     print(f"\nTraining complete! Total time: {time.time() - start_time:.1f}s")
     return model