fix: nil-check reimport result and return projectPath resolution errors

- Add nil check for result after Reimport() call to prevent panic on
  (nil, nil) return
- Return error when user-provided projectPath fails to resolve instead
  of silently ignoring it

Author: Scion Agent (harness-journey-inv)

cmd/harness_config_update.go

@@ -55,9 +55,10 @@ func runHarnessConfigUpdate(cmd *cobra.Command, args []string) error {
 	var gp string
 	if projectPath != "" {
 		resolved, err := config.GetResolvedProjectDir(projectPath)
-		if err == nil {
-			gp = resolved
+		if err != nil {
+			return fmt.Errorf("failed to resolve project path %q: %w", projectPath, err)
 		}
+		gp = resolved
 	} else if projectDir, err := config.GetResolvedProjectDir(""); err == nil {
 		gp = projectDir
 	}
@@ -122,6 +123,9 @@ func updateSingleHarnessConfig(ctx context.Context, hubCtx *HubContext, name, ur
 	if err != nil {
 		return fmt.Errorf("reimport failed: %w", err)
 	}
+	if result == nil {
+		return fmt.Errorf("reimport returned no result for %q", name)
+	}
 
 	if isJSONOutput() {
 		return outputJSON(ActionResult{