[Alerting V2] Restructure Action Policy form with described form groups and progressive disclosure

[miguelmartin-elastic]

📄 Summary

Important

Alerting v2 work under a feature flag disabled by default. See Verification steps > Environment Setup.

Before	After
Screen.Recording.2026-09-14.at.16.10.33.mov	Screen.Recording.2026-09-14.at.16.11.10.mov

Restructures the Action Policy create/edit form so explanatory copy no longer sits in the same visual path as the controls. The four sections now use EuiDescribedFormGroup (description on the left, fields on the right), the Notification controls section shows a live summary on the left, and the Frequency helper text moves into an info-icon popover. Layout / progressive-disclosure only — no schema, dispatch, or API behavior changes.

Changes

• Convert the four form sections (Policy details, Policy scope, Notification controls, Destination) from stacked EuiSplitPanels to EuiDescribedFormGroup, with horizontal dividers between them.
• Move the Notification summary to the left column of Notification controls as a live NotificationSummary component: it reads form state via useWatch and shows the selected notify-per mode description plus the resulting outcome. Removed from below the fields.
• Remove the mode helper text under "Notify per" (now in the summary).
• Replace the Frequency helper text with an info icon next to the label that opens a popover listing every frequency option for the current mode with its explanation (FrequencyHelpTip, EuiPopover — opens on hover, click, and keyboard focus).
• Rename dispatch_config_summary.tsx → notification_summary.tsx (outcome logic kept and single-sourced via exported getDispatchSummary); tests ported and extended.

🧪 Verification steps

⚙️ Environment Setup

Enable Alerting v2 in kibana.dev.yml:

xpack.alerting_v2.enabled: true

Then create at least one action policy, or open Stack Management > Alerts (v2) > Action policies > Create.

✅ Happy Path

1. Open the Action Policy create form. Confirm each section (Policy details, Policy scope, Notification controls, Destination) renders as a described form group with the description on the left and fields on the right, separated by dividers.
2. In Notification controls, confirm the left column shows the "Notification summary" panel with the mode description and the outcome sentence, and no helper text remains under "Notify per".
3. Switch "Notify per" between Episode / Group / Digest and confirm the summary updates live (mode description + outcome).
4. Hover (or click, or tab to) the info icon next to "Frequency". Confirm a light popover lists all frequency options for the current mode, each with its explanation, and that no helper text remains under the Frequency select.
5. Save the policy and confirm it persists as before (defaults and validation unchanged).

⚡️ Edge Cases

• Group mode with no group-by field selected: the summary prompts to select a field.
• Repeat interval field appears only for strategies that need it; validation still fires.
• Frequency popover content differs between per-episode and aggregate (Group/Digest) modes.
• Verify in both classic and solution views.

⏪ Backport rationale

Pre-GA, feature-flagged Alerting v2 work — not backporting.

🔗 References

Relates to https://github.com/elastic/rna-program/issues/1050 (cross-repo; does not auto-close).

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