`UNavigationMenu` issues with slots priority over rendered content

Environment

Operating system	macOS 25.3.0
CPU	Apple M4 Pro (12 cores)
Node.js version	v24.13.0
nuxt/cli version	3.34.0
Package manager	pnpm@10.32.1
Nuxt version	4.4.2
Nitro version	2.13.2
Builder	vite@7.3.1
Config	compatibilityDate, css, devtools, eslint, modules, routeRules
Modules	@nuxt/eslint@1.15.2, @nuxt/ui@4.6.0

Is this bug related to Nuxt or Vue?

Nuxt

Package

v4.x

Version

4.6.0

Reproduction

https://github.com/TotomInc/nuxt-ui-repro/tree/repro/navigation-menu-slots (repro/navigation-menu-slots branch, not master)

Description

Scoped slots (#item-content and #item-trailing) on UNavigationMenu did not behave as expected: dropdown shell with viewport could appear with empty panels (nothing rendered), and custom trailing markup could still show default chevron icons.

item-content

Defining #item-content once (e.g. to customize the mega-menu body per item) caused every top-level item to be treated as having a dropdown.

Items without children still received NavigationMenuTrigger + NavigationMenuContent. If the slot rendered nothing for those rows (v-if="item.children"), the viewport still showed an empty data-slot="content" and empty childList.

item-trailing

Defining #item-trailing should give full control over the trailing area.

Instead, default chevrons (linkTrailingIcon) could still appear on rows where the slot intentionally rendered nothing, because defaults lived inside the same <slot> as fallback content, which interacted badly with createReusableTemplate / ReuseLinkTemplate for nested scoped slots.

Expected behavior

• Dropdown trigger + content should only exist when an item actually has nested entries (children), unless the API explicitly adds another mechanism later.
• When #item-trailing is provided, only that slot should render in the trailing region—no default badge/chevron mix-in for the same row.

Additional context

https://github.com/user-attachments/assets/1c548c72-fd2d-4fc6-876c-4c55cb135386

In the screen-recording, given the source-code of the repro, only the "V" dropdown + chevron should be visible, as this one has children content, while the others don't.

<template>
  <div>
    <UNavigationMenu :items="items">
      <template #item-trailing="{ item }">
        <span v-if="item.children">V</span>
      </template>

      <template #item-content="{ item }">
        <span v-if="item.children">More info...</span>
      </template>
    </UNavigationMenu>
  </div>
</template>

Logs

Start with the linked nuxt-ui-repro repository on the repro/navigation-menu-slots branch and inspect the UNavigationMenu slot implementation. Run the reproduction to observe item-content and item-trailing behavior, then verify that only items with children render dropdown content and that a provided trailing slot suppresses default icons.