[8.18] [Fleet] Add install retry to ensureInstalledPackage (#224265) (#224418)

# Backport

This will backport the following commits from `main` to `8.18`:
- [[Fleet] Add install retry to ensureInstalledPackage
(#224265)](#224265)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Jill
Guyonnet","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-06-18T12:23:47Z","message":"[Fleet]
Add install retry to ensureInstalledPackage (#224265)\n\n##
Summary\n\nCloses
https://github.com/elastic/kibana/issues/213337\n\nWhen requests to
install a package as part of the logic ensuring that a\npackage is
installed are fired concurrently, the second request fails\nwith a 409
`version_conflict_engine_exception`, which causes flakiness\nin tests.
Ignoring these errors in transform installs was already\nattempted in
#177380. This PR adds\na retry
mechanism directly into the package install to consolidate
the\nflow.\n\n### Identify risks\n\nLow probability risk of slower
package policy
creation.","sha":"62f56c884b87e953ef9d6c09e693a70691c28c09","branchLabelMapping":{"^v9.1.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","Team:Fleet","backport:prev-minor","backport:prev-major","v9.1.0"],"title":"[Fleet]
Add install retry to
ensureInstalledPackage","number":224265,"url":"https://github.com/elastic/kibana/pull/224265","mergeCommit":{"message":"[Fleet]
Add install retry to ensureInstalledPackage (#224265)\n\n##
Summary\n\nCloses
https://github.com/elastic/kibana/issues/213337\n\nWhen requests to
install a package as part of the logic ensuring that a\npackage is
installed are fired concurrently, the second request fails\nwith a 409
`version_conflict_engine_exception`, which causes flakiness\nin tests.
Ignoring these errors in transform installs was already\nattempted in
#177380. This PR adds\na retry
mechanism directly into the package install to consolidate
the\nflow.\n\n### Identify risks\n\nLow probability risk of slower
package policy
creation.","sha":"62f56c884b87e953ef9d6c09e693a70691c28c09"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/224265","number":224265,"mergeCommit":{"message":"[Fleet]
Add install retry to ensureInstalledPackage (#224265)\n\n##
Summary\n\nCloses
https://github.com/elastic/kibana/issues/213337\n\nWhen requests to
install a package as part of the logic ensuring that a\npackage is
installed are fired concurrently, the second request fails\nwith a 409
`version_conflict_engine_exception`, which causes flakiness\nin tests.
Ignoring these errors in transform installs was already\nattempted in
#177380. This PR adds\na retry
mechanism directly into the package install to consolidate
the\nflow.\n\n### Identify risks\n\nLow probability risk of slower
package policy
creation.","sha":"62f56c884b87e953ef9d6c09e693a70691c28c09"}}]}]
BACKPORT-->

Co-authored-by: Jill Guyonnet <[email protected]>

Author: kibanamachine

x-pack/platform/plugins/shared/fleet/server/services/epm/packages/install.ts

@@ -106,6 +106,8 @@ import { removeInstallation } from './remove';
 
 export const UPLOAD_RETRY_AFTER_MS = 10000; // 10s
 const MAX_ENSURE_INSTALL_TIME = 60 * 1000;
+const MAX_INSTALL_RETRIES = 5;
+const BASE_RETRY_DELAY_MS = 1000; // 1s
 
 const PACKAGES_TO_INSTALL_WITH_STREAMING = [
   // The security_detection_engine package contains a large number of assets and
@@ -212,16 +214,32 @@ export async function ensureInstalledPackage(options: {
     };
   }
   const pkgkey = Registry.pkgToPkgKey(pkgKeyProps);
-  const installResult = await installPackage({
-    installSource: 'registry',
-    savedObjectsClient,
-    pkgkey,
-    spaceId,
-    esClient,
-    neverIgnoreVerificationError: !force,
-    force: true, // Always force outdated packages to be installed if a later version isn't installed
-    authorizationHeader,
-  });
+
+  const installPackageWithRetries = async (attempt: number): Promise<InstallResult> => {
+    const installResult = await installPackage({
+      installSource: 'registry',
+      savedObjectsClient,
+      pkgkey,
+      spaceId,
+      esClient,
+      neverIgnoreVerificationError: !force,
+      force: true, // Always force outdated packages to be installed if a later version isn't installed
+      authorizationHeader,
+    });
+
+    if (
+      attempt < MAX_INSTALL_RETRIES &&
+      installResult.error?.message.includes('version_conflict_engine_exception')
+    ) {
+      const delayMs = BASE_RETRY_DELAY_MS * 2 ** attempt; // Exponential backoff
+      await new Promise((resolve) => setTimeout(resolve, delayMs));
+      return await installPackageWithRetries(++attempt);
+    } else {
+      return installResult;
+    }
+  };
+
+  const installResult = await installPackageWithRetries(0);
 
   if (installResult.error) {
     const errorPrefix =