[breaking-change] Undocumented breaking changes detected (2026-06-05)

Recent commits introduced a breaking compatibility change that appears undocumented.

## Breaking Changes

### 1. Proofpoint On Demand now blocks upgrades on previously supported Kibana versions
**Commit(s):** [`fed8b77845`](https://github.com/elastic/integrations/commit/fed8b7784575108aa7d262c66d19ee25b2b0fc28)
**PR:** [#18833](https://github.com/elastic/integrations/pull/18833)
**What broke:** The package Kibana compatibility constraint was tightened from `^8.19.0 || ^9.1.0` to `^8.19.16 || ^9.3.5 || ^9.4.0`. Existing users on Kibana `8.19.0-8.19.15` or `9.1.0-9.3.4` can no longer install/upgrade to package `1.10.0`.
**Evidence:**
- `packages/proofpoint_on_demand/manifest.yml` changed in `fed8b77845`:
- before: `conditions.kibana.version: "^8.19.0 || ^9.1.0"`
- after: `conditions.kibana.version: "^8.19.16 || ^9.3.5 || ^9.4.0"`
- `packages/proofpoint_on_demand/changelog.yml` records this release as enhancements only (`version: 1.10.0`), with no breaking-change classification.
**Why undocumented:** PR #18833 describes `sinceTime` backfill support and CEL cleanup, but does not describe a compatibility-breaking minimum-version jump or provide migration guidance. No accompanying README/DEVELOPING/RELEASE note in this change set documents the break.
**Suggested fix:** Add a breaking-change note and migration guidance (minimum supported Kibana versions and upgrade path), or relax the constraint if stricter bounds were unintended.

## Suggested Actions
- [ ] Document this breaking compatibility change in changelog/release documentation as a breaking change
- [ ] Add migration guidance for users on older Kibana versions

> [!NOTE]
>
> 🔒 Integrity filter blocked 8 items
>
> The following items were blocked because they don't meet the GitHub integrity level.
>
> - [#19343](https://github.com/elastic/integrations/pull/19343) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19385](https://github.com/elastic/integrations/pull/19385) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19383](https://github.com/elastic/integrations/pull/19383) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19320](https://github.com/elastic/integrations/pull/19320) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19390](https://github.com/elastic/integrations/pull/19390) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#18833](https://github.com/elastic/integrations/pull/18833) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19144](https://github.com/elastic/integrations/pull/19144) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#19376](https://github.com/elastic/integrations/pull/19376) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
>
> To allow these resources, lower `min-integrity` in your GitHub frontmatter:
>
> ```yaml
> tools:
> github:
> min-integrity: approved # merged | approved | unapproved | none
> ```
>
>

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