Add lazy warehouse resolution with smart discovery

Implements intelligent warehouse auto-discovery:
- Add GetWarehouseID() with smart fallback chain:
  1. Check DATABRICKS_WAREHOUSE_ID environment variable
  2. Query available warehouses via API
  3. Prefer RUNNING warehouses
  4. Fall back to STOPPED warehouses (auto-start)
  5. Use first available warehouse
- Cache warehouse ID in session after first resolution
- Remove warehouse ID from CLI flags and config
- Update NewDatabricksRestClient and ResourcesFromEnv to use GetWarehouseID

Eliminates need to specify warehouse ID upfront.

Author: fjakobs

experimental/apps-mcp/lib/middlewares/warehouse.go

@@ -0,0 +1,87 @@
+package middlewares
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/url"
+
+	"github.com/databricks/cli/experimental/apps-mcp/lib/session"
+	"github.com/databricks/cli/libs/env"
+	"github.com/databricks/databricks-sdk-go/httpclient"
+	"github.com/databricks/databricks-sdk-go/service/sql"
+)
+
+func GetWarehouseID(ctx context.Context) (string, error) {
+	sess, err := session.GetSession(ctx)
+	if err != nil {
+		return "", err
+	}
+	warehouseID, ok := sess.Get("warehouse_id")
+	if !ok {
+		warehouse, err := getDefaultWarehouse(ctx)
+		if err != nil {
+			return "", err
+		}
+		warehouseID = warehouse.Id
+		sess.Set("warehouse_id", warehouseID.(string))
+	}
+
+	return warehouseID.(string), nil
+}
+
+func getDefaultWarehouse(ctx context.Context) (*sql.EndpointInfo, error) {
+	// first resolve DATABRICKS_WAREHOUSE_ID env variable
+	warehouseID := env.Get(ctx, "DATABRICKS_WAREHOUSE_ID")
+	if warehouseID != "" {
+		w := MustGetDatabricksClient(ctx)
+		warehouse, err := w.Warehouses.Get(ctx, sql.GetWarehouseRequest{
+			Id: warehouseID,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("get warehouse: %w", err)
+		}
+		return &sql.EndpointInfo{
+			Id: warehouse.Id,
+		}, nil
+	}
+
+	apiClient, err := MustGetApiClient(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	apiPath := "/api/2.0/sql/warehouses"
+	params := url.Values{}
+	params.Add("skip_cannot_use", "true")
+	fullPath := fmt.Sprintf("%s?%s", apiPath, params.Encode())
+
+	var response sql.ListWarehousesResponse
+	err = apiClient.Do(ctx, "GET", fullPath, httpclient.WithResponseUnmarshal(&response))
+	if err != nil {
+		return nil, err
+	}
+
+	warehouses := response.Warehouses
+
+	if len(warehouses) == 0 {
+		return nil, errors.New("no warehouses found")
+	}
+
+	// Prefer RUNNING warehouses
+	for i := range warehouses {
+		if warehouses[i].State == sql.StateRunning {
+			return &warehouses[i], nil
+		}
+	}
+
+	// Fall back to STOPPED warehouses (they auto-start when queried)
+	for i := range warehouses {
+		if warehouses[i].State == sql.StateStopped {
+			return &warehouses[i], nil
+		}
+	}
+
+	// Return first available warehouse regardless of state
+	return &warehouses[0], nil
+}

experimental/apps-mcp/lib/providers/databricks/databricks.go

@@ -435,9 +435,9 @@ type DatabricksRestClient struct {
 func NewDatabricksRestClient(ctx context.Context, cfg *mcp.Config) (*DatabricksRestClient, error) {
 	client := middlewares.MustGetDatabricksClient(ctx)
 
-	warehouseID := os.Getenv("DATABRICKS_WAREHOUSE_ID")
-	if warehouseID == "" {
-		return nil, errors.New("DATABRICKS_WAREHOUSE_ID not configured")
+	warehouseID, err := middlewares.GetWarehouseID(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get warehouse ID: %w", err)
 	}
 
 	return &DatabricksRestClient{

experimental/apps-mcp/lib/providers/databricks/deployment.go

@@ -3,11 +3,11 @@ package databricks
 import (
 	"context"
 	"fmt"
-	"os"
 	"os/exec"
 	"time"
 
 	mcp "github.com/databricks/cli/experimental/apps-mcp/lib"
+	"github.com/databricks/cli/experimental/apps-mcp/lib/middlewares"
 	"github.com/databricks/cli/libs/cmdctx"
 	"github.com/databricks/databricks-sdk-go/service/apps"
 	"github.com/databricks/databricks-sdk-go/service/iam"
@@ -102,8 +102,11 @@ func DeployApp(ctx context.Context, cfg *mcp.Config, appInfo *apps.App) error {
 	return nil
 }
 
-func ResourcesFromEnv(cfg *mcp.Config) (*apps.AppResource, error) {
-	warehouseID := os.Getenv("DATABRICKS_WAREHOUSE_ID")
+func ResourcesFromEnv(ctx context.Context, cfg *mcp.Config) (*apps.AppResource, error) {
+	warehouseID, err := middlewares.GetWarehouseID(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get warehouse ID: %w", err)
+	}
 
 	return &apps.AppResource{
 		Name:        "base",

experimental/apps-mcp/lib/providers/deployment/provider.go

@@ -289,7 +289,7 @@ func (p *Provider) getOrCreateApp(ctx context.Context, name, description string,
 
 	log.Infof(ctx, "App not found, creating new app: name=%s", name)
 
-	resources, err := databricks.ResourcesFromEnv(p.config)
+	resources, err := databricks.ResourcesFromEnv(ctx, p.config)
 	if err != nil {
 		return nil, err
 	}