Fix optimized attention mask handling for training

- Fix mask format conversion (float to boolean) for scaled_dot_product_attention
- Fix mask dimensions for proper broadcasting [batch, 1, seq_len, seq_len]
- Resolve conflict between is_causal and custom mask parameters
- Enable training with optimized attention and KV caching

models/optimized_attention.py

@@ -130,11 +130,30 @@ class OptimizedMultiHeadAttention(nn.Module):
         # Compute attention scores with optimized computation
         if self.use_flash_attention and hasattr(F, 'scaled_dot_product_attention'):
             # Use PyTorch's optimized scaled dot product attention
+            # Prepare mask for scaled_dot_product_attention
+            # Note: scaled_dot_product_attention expects boolean mask where True=attend, False=mask
+            # Our mask is float where 1.0=valid, 0.0=masked, so we need to convert
+            attn_mask = None
+            if mask is not None:
+                # Convert float mask to boolean: 1.0 -> True (attend), 0.0 -> False (mask)
+                if mask.dim() == 2:
+                    # [seq_len, seq_len] -> [1, 1, seq_len, seq_len] for broadcasting
+                    attn_mask = (mask > 0.5).unsqueeze(0).unsqueeze(0)
+                elif mask.dim() == 3:
+                    # [batch, seq_len, seq_len] -> [batch, 1, seq_len, seq_len] for broadcasting
+                    attn_mask = (mask > 0.5).unsqueeze(1)
+                else:
+                    attn_mask = (mask > 0.5)
+            
+            # Use causal masking only if no custom mask is provided
+            # If we have a custom mask, it should already include causal masking
+            use_causal = self.causal and (attn_mask is None)
+            
             output = F.scaled_dot_product_attention(
                 Q, K, V,
-                attn_mask=mask,
+                attn_mask=attn_mask,
                 dropout_p=self.dropout.p if self.training else 0.0,
-                is_causal=self.causal,
+                is_causal=use_causal,
             )
             attention_weights = None  # Flash attention doesn't return weights
         else: