fix: nested Block Grid delete navigates to parent block (#312)

[rickbutterfield]

Fixes #312

Problem

Deleting a child element inside a nested Block Grid container reloads the backoffice and opens the parent container's workspace instead of deleting the child. Deleting a top-level block works fine.

Root cause

Each block preview is rendered inside an <a class="block-preview-edit" href="{block edit route}">. When a Block Grid block has areas, Umbraco renders the child block entries — including their action bars — inside that anchor. A guard cancels the anchor's navigation for action-bar clicks so they don't trigger the parent block's edit route.

That guard ran in the bubble phase. Umbraco 17.5 wraps action buttons in <umb-block-action>, which calls stopPropagation() on the click before it can bubble to the ancestor anchor — so the guard never ran and its preventDefault() never fired. stopPropagation() does not cancel the anchor's default navigation, so the browser followed the parent block's href, reloading into the parent workspace.

Bisected against Umbraco: reproduces on 17.5.2, works on 17.3.4, with byte-identical BlockPreview click-handling code — i.e. it is triggered by the 17.5 backoffice DOM change, not a BlockPreview regression. (The same code is present on v5/dev, v6/main, and the released 5.4.3, matching the reporter's environments.)

Fix

Add a capture-phase guard on the preview host that cancels the anchor's default navigation for block-action clicks (delete / copy / scale), while letting the edit button through so it can still open the block workspace. The capture phase runs before propagation can be stopped, so it works on 17.5+ and remains correct on earlier versions.

The decision is extracted into a pure isBlockActionNavigation(path) function and unit tested.

Testing

• 16/16 frontend unit tests pass, including 5 new cases in nested-block-action-navigation.test.ts (17.5 umb-block-action wrapper, older no-wrapper action bar, plain body click, edit-button exception, scale handle).
• .NET library builds clean in Release.
• Manual end-to-end on Umbraco 17.5.2 (test site "Home"):
  • Delete nested "See our solutions" → confirm dialog → child is deleted, no page reload, no parent workspace ✅
  • Edit pencil on the nested child → still opens the child block ✅

Notes

• Also bumps the development test site to Umbraco 17.5.2 (separate commit), which is what surfaces the regression.
• The same fix should be forward-ported to the v6 line (identical click-handling code), consistent with "Property Type is Invalid" #291/Block Grid area previews can render before layoutAreas are available in 5.4.0 #293.

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