More debugging code for replyTo address (#3053)

The  replyTo header works in manual tests. Add code emulating
BillingEmailUtils behavior and see if that causes the problem.

Also experimenting not to set the From header in GmaiClient, since
whatever we set is overridden anyway.

core/src/main/java/google/registry/batch/BatchModule.java

@@ -54,9 +54,9 @@ public class BatchModule {
   static final int DEFAULT_MAX_QPS = 10;
 
   @Provides
-  @Parameter("sender")
-  static String provideSender(HttpServletRequest req) {
-    return extractRequiredParameter(req, "sender");
+  @Parameter("replyTo")
+  static String provideReplyTo(HttpServletRequest req) {
+    return extractRequiredParameter(req, "replyTo");
   }
 
   @Provides

core/src/main/java/google/registry/batch/CannedScriptExecutionAction.java

@@ -18,7 +18,9 @@ import static google.registry.request.Action.Method.GET;
 import static google.registry.request.Action.Method.POST;
 
 import com.google.api.services.gmail.Gmail;
+import com.google.common.collect.ImmutableList;
 import com.google.common.flogger.FluentLogger;
+import com.google.common.net.MediaType;
 import dagger.Lazy;
 import google.registry.config.RegistryConfig.Config;
 import google.registry.groups.GmailClient;
@@ -31,6 +33,7 @@ import google.registry.util.Retrier;
 import jakarta.inject.Inject;
 import jakarta.mail.internet.AddressException;
 import jakarta.mail.internet.InternetAddress;
+import java.util.Optional;
 
 /**
  * Action that executes a canned script specified by the caller.
@@ -62,13 +65,16 @@ public class CannedScriptExecutionAction implements Runnable {
   @Inject Response response;
 
   @Inject
-  @Parameter("sender")
-  String sender;
+  @Parameter("replyTo")
+  String replyTo;
 
   @Inject
   @Parameter("receiver")
   String receiver;
 
+  @Config("invoiceReplyToEmailAddress")
+  Optional<InternetAddress> replyToEmailAddressFromConfig;
+
   @Inject
   CannedScriptExecutionAction() {}
 
@@ -77,20 +83,36 @@ public class CannedScriptExecutionAction implements Runnable {
     // For b/510340944, validating a new G Workspace user can send email. Code below can be
     // removed or changed afterward.
     try {
-      logger.atInfo().log("Sending email from %s to %s", sender, receiver);
+      logger.atInfo().log("Sending email to %s with replyTo %s", receiver, replyTo);
       GmailClient gmailClient =
-          new GmailClient(
-              gmail, retrier, isEmailSendingEnabled, sender, sender, new InternetAddress(sender));
+          new GmailClient(gmail, retrier, isEmailSendingEnabled, new InternetAddress(replyTo));
       gmailClient.sendEmail(
           EmailMessage.newBuilder()
               .addRecipient(new InternetAddress(receiver))
-              .setSubject(String.format("Email send test from %s", sender))
-              .setBody(String.format("This is a test email sent from %s to %s.", sender, receiver))
+              .setSubject(String.format("Email with manually set replyTo header %s", replyTo))
+              .setBody("See subject")
               .build());
-      response.setPayload("Email sent successfully.");
+
+      try {
+        Thread.sleep(1000);
+      } catch (InterruptedException e) {
+        Thread.currentThread().interrupt();
+      }
+
+      gmailClient.sendEmail(
+          EmailMessage.newBuilder()
+              .setSubject(
+                  String.format(
+                      "Email with injected replyTo header %s", replyToEmailAddressFromConfig))
+              .setBody("See header")
+              .setRecipients(ImmutableList.of(new InternetAddress(receiver)))
+              .setReplyToEmailAddress(replyToEmailAddressFromConfig)
+              .setContentType(MediaType.HTML_UTF_8)
+              .build());
+      response.setPayload("Emails sent successfully.");
     } catch (AddressException e) {
       logger.atWarning().withCause(e).log(
-          "Invalid email address: sender=%s, receiver=%s", sender, receiver);
+          "Invalid email address: sender=%s, receiver=%s", replyTo, receiver);
       response.setStatus(400);
       response.setPayload("Invalid email address provided.");
     } catch (Exception e) {

core/src/main/java/google/registry/groups/GmailClient.java

@@ -56,9 +56,9 @@ public final class GmailClient {
   private final InternetAddress outgoingEmailAddressWithUsername;
   private final InternetAddress replyToEmailAddress;
 
-  // TODO(b/510340944): make package private after feature is rolled out
+  // TODO(b/510340944): drop sender info. Sender is determined by the Gmail credential owner.
   @Inject
-  public GmailClient(
+  GmailClient(
       Lazy<Gmail> gmail,
       Retrier retrier,
       @Config("isEmailSendingEnabled") boolean isEmailSendingEnabled,
@@ -78,6 +78,20 @@ public final class GmailClient {
     }
   }
 
+  // TODO(b/510340944): Remove this experiment method
+  public GmailClient(
+      Lazy<Gmail> gmail,
+      Retrier retrier,
+      @Config("isEmailSendingEnabled") boolean isEmailSendingEnabled,
+      @Config("replyToEmailAddress") InternetAddress replyToEmailAddress) {
+
+    this.gmail = gmail;
+    this.retrier = retrier;
+    this.isEmailSendingEnabled = isEmailSendingEnabled;
+    this.replyToEmailAddress = replyToEmailAddress;
+    this.outgoingEmailAddressWithUsername = null;
+  }
+
   /**
    * Sends {@code emailMessage} using {@link Gmail}.
    */
@@ -117,7 +131,9 @@ public final class GmailClient {
     try {
       MimeMessage msg =
           new MimeMessage(Session.getDefaultInstance(new Properties(), /* authenticator= */ null));
-      msg.setFrom(this.outgoingEmailAddressWithUsername);
+      if (this.outgoingEmailAddressWithUsername != null) {
+        msg.setFrom(this.outgoingEmailAddressWithUsername);
+      }
       msg.setReplyTo(
           new InternetAddress[] {emailMessage.replyToEmailAddress().orElse(replyToEmailAddress)});
       msg.addRecipients(