[Significant events] Improving the UI/UX around model selection and run configuration popover

[boriskirov]

Summary

This is UX and UI focused PR for #261588 which is focusing on improving the way how you handle configuration runs and model selection from the pop over for Generate KI and Discovery Significant events.

Screen.Recording.2026-04-08.at.15.18.09.mov

[macroscopeapp]

Approvability

Verdict: Needs human review

UI/UX refactor replacing popover components with split button menus for model selection. While the changes are self-contained to the significant events feature and don't alter core business logic, all files are owned by @elastic/obs-sig-events-team and the author is not a designated owner, warranting team review.

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[boriskirov]

@elasticmachine merge upstream

[achyutjhunjhunwala]

I have added 2 nit's which would be great to fix. apart from that, everything else looks good. LGTM

[achyutjhunjhunwala]

nit: EuiSelectable with bare singleSelection allows the user to click an already-checked item to deselect it, leaving zero connectors selected. The handleChange callback guards with if (selected?.key), so no crash occurs, but the user gets a confusing silent no-op where their click does nothing.

Using singleSelection="always" prevents deselection entirely -- this pattern is used widely across the Kibana codebase.

[boriskirov]

thank you @achyutjhunjhunwala

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: b68b63b

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
streamsApp	1817	1819	+2

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
streamsApp	1.9MB	1.9MB	+660.0B

History

• 💛 Build #425587 was flaky 3bd3d29
• 💔 Build #424567 failed 36c9703
• 💔 Build #424544 failed e770668
• 💔 Build #424531 failed 789027b