update comments in accordance with code review

mmv1/third_party/terraform/transport/config.go.tmpl

@@ -438,9 +438,10 @@ func (c *Config) LoadAndValidate(ctx context.Context) error {
 	cleanCtx := context.WithValue(ctx, oauth2.HTTPClient, cleanhttp.DefaultClient())
 	clientOptions := []option.ClientOption{option.WithTokenSource(tokenSource)}
 
-	// 'X-Goog-User-Project' gets set by a transport layer within transport.NewHTTPClient
-	// setting explicitly here to override the setting of it by underlying utility function.
-	//  b/360405077#comment8
+    // The client libraries allow setting the GOOGLE_CLOUD_QUOTA_PROJECT environment variable 
+	// directly, which unintentionally takes precedence over provider settings. Ensure that 
+	// provider settings take precedence by applying to the client library's client directly
+	// b/360405077#comment8 - go/tpg-issue/17882
 	if c.UserProjectOverride && c.BillingProject != "" {
 		quotaProject :=  c.BillingProject
 		clientOptions = append(clientOptions, option.WithQuotaProject(quotaProject))
@@ -476,12 +477,10 @@ func (c *Config) LoadAndValidate(ctx context.Context) error {
 
 	// Ensure $userProject is set for all HTTP requests using the client if specified by the provider config
 	// See https://cloud.google.com/apis/docs/system-parameters
-	// We explicitly set this header for logging visibility, even though 
-	// option.WithQuotaProject will automatically set it in the client.
-	// This duplicate setting ensures the header appears in our request logs
-	// since our logging transport sits on top of the Google client library's
-	// internal transport that would also sets this header.
-	// option.WithQuotaProject will automatically set it in the client
+	// option.WithQuotaProject automatically sets the quota project in the client.
+	// However, this setting won't appear in our request logs since our logging
+	// transport sits above the Google client's internal transport. To ensure
+	// visibility in debug logging, we explicitly set the quota project here as well.
 	if c.UserProjectOverride && c.BillingProject != "" {
 		headerTransport.Set("X-Goog-User-Project", c.BillingProject)
 	}