[breaking-change] Undocumented breaking changes detected (2026-04-02)

Recent commits introduced a breaking change that appears undocumented.

## Breaking Changes

### 1. `ess_billing` dropped Kibana 8.x compatibility without migration note
**Commit(s):** [`531cf02aef`](https://github.com/elastic/integrations/commit/531cf02aefbc394f3dd0ecf995b4226e865b6987)
**PR:** https://github.com/elastic/integrations/pull/17793
**What broke:** The package compatibility gate changed from allowing Kibana `^8.18.0 || ^9.0.0` to requiring `^9.3.0`, which blocks existing 8.x users from installing/upgrading this integration.
**Evidence:**
- `packages/ess_billing/manifest.yml:13` now requires `version: "^9.3.0"`.
- In the same commit diff, previous value was `^8.18.0 || ^9.0.0`.
- `packages/ess_billing/changelog.yml:2-6` only describes a bugfix (“Fix incorrect handling of credit data”), with no compatibility/migration note.
- `packages/ess_billing/docs/README.md:32` still says this integration is available agentless from cluster version 8.17 onward, which conflicts with the new manifest constraint.
**Why undocumented:** The PR/package changelog does not mention this as a breaking compatibility change, and package docs were not updated with migration guidance.
**Suggested fix:** Add an explicit breaking-change entry and migration guidance for 8.x users; update `packages/ess_billing/docs/README.md` compatibility text to match manifest constraints.

## Suggested Actions
- [ ] Document this compatibility break in release/changelog notes
- [ ] Add migration guidance for users pinned to 8.x stacks
- [ ] Update package README compatibility requirements to match `manifest.yml`

> [!NOTE]
>
> 🔒 Integrity filtering filtered 8 items
>
> Integrity filtering activated and filtered the following items during workflow execution.
> This happens when a tool call accesses a resource that does not meet the required integrity or secrecy level of the workflow.
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> - [#18119](https://github.com/elastic/integrations/pull/18119) (`search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - [#18135](https://github.com/elastic/integrations/pull/18135) (`search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - [#18190](https://github.com/elastic/integrations/pull/18190) (`search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - [#17793](https://github.com/elastic/integrations/pull/17793) (`search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - pr:elastic/integrations#18119 (`pull_request_read`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - pr:elastic/integrations#18170 (`pull_request_read`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - pr:elastic/integrations#17793 (`pull_request_read`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/integrations#unknown (`search_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
>
>

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