fix: restore CWD after local_preview MCP tool to support subdirectory workspaces (#390)

When the MCP server is started from a subdirectory of a git repository,
createLocalPreviewRun archives from that subdirectory rather than the repo
root, causing Spacelift to fail with "project root ... does not exist".

Save the original CWD before calling createLocalPreviewRun with
FindRepositoryRoot=true (same as the CLI), then defer a restore so the
long-running MCP server process has its working directory restored after
each call.

Co-authored-by: Rocky Olsen <rolsen@lucidchart.com>

Author: thenoid

internal/cmd/stack/mcp.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/mark3labs/mcp-go/mcp"
@@ -639,6 +640,15 @@ func registerLocalPreviewTool(s *server.MCPServer, options McpOptions) {
 
 		awaitForCompletion := request.GetString("await_for_completion", "true") == "true"
 
+		// Save and restore CWD: createLocalPreviewRun with FindRepositoryRoot=true
+		// calls os.Chdir() to the git root. We restore afterward so the long-running
+		// MCP server process isn't left with a permanently changed working directory.
+		origDir, err := os.Getwd()
+		if err != nil {
+			return nil, fmt.Errorf("failed to get working directory: %w", err)
+		}
+		defer os.Chdir(origDir) //nolint: errcheck
+
 		// Create a string builder to capture output
 		var outputBuilder strings.Builder
 
@@ -649,7 +659,7 @@ func registerLocalPreviewTool(s *server.MCPServer, options McpOptions) {
 				EnvironmentVars:    envVars,
 				Targets:            targets,
 				Path:               path,
-				FindRepositoryRoot: false,
+				FindRepositoryRoot: true,
 				DisregardGitignore: false,
 				UseHeaders:         options.UseHeadersForLocalPreview,
 				NoUpload:           false,