[9.1] [CI] Disable moon cache for build (#238404) (#238424)

# Backport

This will backport the following commits from `main` to `9.1`:
- [[CI] Disable moon cache for build
(#238404)](#238404)

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

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

<!--BACKPORT [{"author":{"name":"Alex
Szabo","email":"alex.szabo@elastic.co"},"sourceCommit":{"committedDate":"2025-10-10T11:15:38Z","message":"[CI]
Disable moon cache for build (#238404)\n\n## Summary\nKibana's build
seems to be breaking on a `yarn` command, it's not quite\nclear how/why,
but this attempts to disable cache for that step, to get\nit
working.","sha":"f9749b59a1e4dc1464e8b5176522aa61bbaa0d70","branchLabelMapping":{"^v9.3.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","backport:all-open","v9.3.0"],"title":"[CI]
Disable moon cache for
build","number":238404,"url":"https://github.com/elastic/kibana/pull/238404","mergeCommit":{"message":"[CI]
Disable moon cache for build (#238404)\n\n## Summary\nKibana's build
seems to be breaking on a `yarn` command, it's not quite\nclear how/why,
but this attempts to disable cache for that step, to get\nit
working.","sha":"f9749b59a1e4dc1464e8b5176522aa61bbaa0d70"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.3.0","branchLabelMappingKey":"^v9.3.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/238404","number":238404,"mergeCommit":{"message":"[CI]
Disable moon cache for build (#238404)\n\n## Summary\nKibana's build
seems to be breaking on a `yarn` command, it's not quite\nclear how/why,
but this attempts to disable cache for that step, to get\nit
working.","sha":"f9749b59a1e4dc1464e8b5176522aa61bbaa0d70"}}]}]
BACKPORT-->

Co-authored-by: Alex Szabo <alex.szabo@elastic.co>

Author: kibanamachine

kbn_pm/src/commands/build_shared_packages.mjs

@@ -9,7 +9,7 @@
 
 import { run } from '../lib/spawn.mjs';
 
-/** @type {import("../lib/command").Command} */
+/** @type {import('../lib/command').Command} */
 export const command = {
   name: 'build-shared',
   intro: 'Builds shared packages with webpack',
@@ -35,6 +35,10 @@ export const command = {
       [':build-webpack'].concat(!cache ? ['-u'] : []).concat(dist ? ['--', '--dist'] : []),
       {
         pipe: !quiet,
+        env: {
+          ...process.env,
+          ...(!cache ? { MOON_CACHE: 'off' } : {}),
+        },
       }
     );
 

src/dev/build/tasks/build_packages_task.ts

@@ -109,6 +109,7 @@ export const BuildPackages: Task = {
     await buildWebpackBundles({
       quiet: false,
       dist: true,
+      noCache: true,
     });
 
     const transformConfig: TransformConfig = {
@@ -307,8 +308,20 @@ export const BuildPackages: Task = {
   },
 };
 
-export async function buildWebpackBundles({ quiet, dist }: { quiet: boolean; dist: boolean }) {
-  const options = [quiet ? ['--quiet'] : [], dist ? ['--dist'] : []].flat();
+export async function buildWebpackBundles({
+  quiet,
+  dist,
+  noCache,
+}: {
+  quiet: boolean;
+  dist: boolean;
+  noCache?: boolean;
+}) {
+  const options = [
+    quiet ? ['--quiet'] : [],
+    dist ? ['--dist'] : [],
+    noCache ? ['--no-cache'] : [],
+  ].flat();
   const stdio: StdioOption[] = quiet
     ? ['ignore', 'pipe', 'pipe']
     : ['inherit', 'inherit', 'inherit'];