Add warning for existing build/ directory in env setup

The env_setup.sh script now checks for an existing build/ directory
before installing the forge package. If found, it warns the user that
the directory may contain artifacts from a previous pip installation
that could interfere with the current installation.

The user is prompted to continue or cancel, with instructions on how
to manually remove the build/ directory if they encounter issues.

Author: casteryh

.meta/mast/env_setup.sh

@@ -259,8 +259,26 @@ else
     log_warn "Skipping monarch torch import hack (monarch may not be installed yet)"
 fi
 
-# Step 6: Install forge package
-log_info "Step 6: Installing forge package..."
+# Step 6: Check for existing build directory and warn user
+log_info "Step 6: Checking for existing build directory..."
+if [ -d "$FORGE_REPO_DIR/build" ]; then
+    log_warn "Detected existing build/ directory at: $FORGE_REPO_DIR/build"
+    log_warn "This directory may contain artifacts from a previous pip installation"
+    log_warn "that could interfere with the current installation."
+    log_warn "If you encounter issues, manually remove it with: rm -rf $FORGE_REPO_DIR/build"
+    echo ""
+    read -p "$(echo -e ${YELLOW}Do you want to continue anyway? [y/N]:${NC} )" -n 1 -r
+    echo ""
+    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+        log_info "Installation cancelled by user"
+        log_info "You can manually remove the build/ directory with: rm -rf $FORGE_REPO_DIR/build"
+        exit 0
+    fi
+    log_warn "Continuing with existing build/ directory. Things might go wrong!"
+fi
+
+# Step 7: Install forge package
+log_info "Step 7: Installing forge package..."
 pip install --no-deps --force-reinstall .
 if [ $? -ne 0 ]; then
     log_error "Failed to install forge package"
@@ -298,7 +316,7 @@ pip list | grep -E "(forge|monarch)" || log_warn "No forge/monarch packages foun
 log_info "Environment setup complete! You can now run your scripts."
 log_info "Mounted workspace available at: /mnt/wsfuse"
 
-# Step 6: Ask user to deactivate and activate conda env conda environment
+# Step 8: Ask user to deactivate and activate conda env conda environment
 echo ""
 log_info "Installation completed successfully!"
 echo ""