See a summary of rule health and gap status in the Rule Monitoring Overview panel

## Summary

The Rule Monitoring tab's overview panel now includes two new summaries: a last-response breakdown showing how many rules succeeded, failed, returned a warning, or have no response yet, and a gap breakdown showing total unfilled, in-progress, and filled gap duration along with how many rules fall into each gap-fill status. The panel is backed by an extended internal gaps API that now returns this aggregated summary data alongside per-space health data for the last-response counts.

**Why this needs docs:** The diff (new last_response_summary_chart and rule_gap_summary_chart components, extended gaps API schema/route, and matching screenshot) confirms the new charts described in the PR, and they extend a panel that docs already partially describe, so the existing page needs updating rather than a new page.

## Resources

- PR [#252327](https://github.com/elastic/kibana/pull/252327) — [Security Solution] Adds a Rule Monitoring Overview panel to the Rules Monitoring tab

Screenshots from PR


## Availability

| Channel | Details |
|---------|---------|
| **Stack** | v9.4.0 |
| **Serverless** | Mar 9–Mar 13 |
| **Feature flag** | None — active by default |

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*Created with [Docs Quest Scanner](https://github.com/florent-leborgne/docs-quest-scanner) by @nastasha-solomon*

## Suggested edits

[Fill rule execution gaps](https://www.elastic.co/docs/solutions/security/detect-and-alert/fill-rule-gaps) > Rule Monitoring tab
- **What the docs say:** Describes the panel above the Rules table only in terms of the "Rules with gaps" metric (rules with gaps vs. rules with all gaps filled), varying by stack version, and notes the panel is expanded by default since 9.4. It does not mention any last-response or gap-duration/fill-status breakdown charts.
- **What to add:** Update the "Rule Monitoring tab" section to describe the new Rule Monitoring Overview charts: a last-response summary (counts of rules that succeeded, failed, returned a warning, or have no response yet) and a gap breakdown (total unfilled/in-progress/filled gap duration and rule counts per gap-fill status). Applies from 9.4.0 and in serverless (rolling out around Mar 9-13, 2026).