wait for the Agent MSI product registration and InstallPath registry … (#53656)

…value to be restored after rollback before asserting the installer state

### What does this PR do?
This PR addresses a race condition in `test/new-e2e/tests/installer/windows/TestExtensionPersistence` by waiting for the Agent MSI product registration and InstallPath registry value to be restored after rollback before asserting the installer state.

### Motivation
[WINA-2821](https://datadoghq.atlassian.net/browse/WINA-2821)

### Describe how you validated your changes
Validation with stress test.

### Additional Notes


[WINA-2821]: https://datadoghq.atlassian.net/browse/WINA-2821?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Co-authored-by: hongshi.guo <hongshi.guo@datadoghq.com>

Author: guohdd

test/new-e2e/tests/installer/windows/agent_upgrade_test.go

@@ -9,6 +9,7 @@ package installer
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -903,11 +904,38 @@ func (s *testAgentUpgradeSuite) waitForExperimentMSIRollback() {
 	// so we can wait for the stable version to be placed on disk once again via MSI rollback
 	err = s.waitForInstallerVersion(s.StableAgentVersion().Version())
 	s.Require().NoError(err)
+	// The installer binary can be present before Windows Installer has finished
+	// restoring product registration and Agent registry values.
+	err = s.waitForAgentMSIInstalledState()
+	s.Require().NoError(err)
 	// and wait again to ensure the stable service is running
 	err = s.WaitForInstallerService("Running")
 	s.Require().NoError(err)
 }
 
+func (s *testAgentUpgradeSuite) waitForAgentMSIInstalledState() error {
+	_, err := backoff.Retry(context.Background(), func() (any, error) {
+		productCode, err := windowsagent.GetDatadogAgentProductCode(s.Env().RemoteHost)
+		if err != nil {
+			return nil, fmt.Errorf("Datadog Agent product is not registered yet: %w", err)
+		}
+		if strings.TrimSpace(productCode) == "" {
+			return nil, errors.New("Datadog Agent product code is empty")
+		}
+
+		installPath, err := windowsagent.GetInstallPathFromRegistry(s.Env().RemoteHost)
+		if err != nil {
+			return nil, fmt.Errorf("Datadog Agent InstallPath is not restored yet: %w", err)
+		}
+		if strings.TrimSpace(installPath) == "" {
+			return nil, errors.New("Datadog Agent InstallPath is empty")
+		}
+
+		return nil, nil
+	}, backoff.WithBackOff(backoff.NewConstantBackOff(5*time.Second)), backoff.WithMaxTries(100))
+	return err
+}
+
 // setExperimentMSIArgs stores a list of MSI options for the installer to provide to the MSI when starting an experiment.
 func (s *testAgentUpgradeSuite) setExperimentMSIArgs(args []string) {
 	err := windowscommon.SetRegistryMultiString(s.Env().RemoteHost, `HKLM:SOFTWARE\Datadog\Datadog Agent`, "StartExperimentMSIArgs", args)

test/new-e2e/tests/installer/windows/persisting_extensions_test.go

@@ -255,6 +255,9 @@ func (s *testExtensionsSuite) TestExtensionRestoredOnMSIRollback() {
 	err = s.waitForInstallerVersion(s.StableAgentVersion().Version())
 	s.Require().NoError(err)
 
+	err = s.waitForAgentMSIInstalledState()
+	s.Require().NoError(err)
+
 	s.Require().Host(s.Env().RemoteHost).
 		HasDatadogInstaller().
 		WithVersionMatchPredicate(func(version string) {