fix: unwrap Fragment vnodes in Slot before cloning

<slot /> used as a passthrough outlet inside an SFC template (e.g.
DialogTrigger.vue's <Primitive as-child><slot /></Primitive>) resolves
through Vue's renderSlot() helper, which always wraps the forwarded
content in a Fragment vnode -- even when there's exactly one real
child. Slot was cloning that inert Fragment wrapper instead of the
real child, so attrs merged onto asChild-forwarded elements (data-slot,
aria-*, the click handler) silently vanished. Found via manual
Storybook verification: the Dialog trigger rendered but never opened
the dialog on click.

Unwrap single-child Fragments before merging/cloning, and add a
regression test through a real SFC fixture (a raw h()-based test
doesn't reproduce this, since it never goes through renderSlot()).

packages/library/src/lib/slot.ts

@@ -1,5 +1,16 @@
 import type { VNode } from 'vue'
-import { cloneVNode, defineComponent, mergeProps } from 'vue'
+import { Fragment, cloneVNode, defineComponent, mergeProps } from 'vue'
+
+// `<slot />` used as a passthrough outlet resolves through Vue's `renderSlot()`
+// helper, which always wraps the forwarded content in a Fragment vnode (for
+// diffing), even when there's exactly one real child inside. Unwrap it so we
+// clone the actual element/component vnode instead of the inert wrapper.
+function unwrapFragment(vnode: VNode): VNode {
+  if (vnode.type === Fragment && Array.isArray(vnode.children) && vnode.children.length === 1) {
+    return unwrapFragment(vnode.children[0] as VNode)
+  }
+  return vnode
+}
 
 export default defineComponent({
   name: 'Slot',
@@ -10,7 +21,7 @@ export default defineComponent({
       if (children.length !== 1) {
         throw new Error('Slot requires exactly one child element')
       }
-      const child = children[0] as VNode
+      const child = unwrapFragment(children[0] as VNode)
       return cloneVNode(child, mergeProps(attrs, (child.props ?? {}) as Record<string, unknown>))
     }
   },

packages/library/tests/fixtures/SlotPassthrough.vue

@@ -0,0 +1,11 @@
+<script setup lang="ts">
+import { Primitive } from '@/lib/primitive'
+
+defineProps<{ asChild?: boolean }>()
+</script>
+
+<template>
+  <Primitive as="button" :as-child="asChild" type="button" data-slot="passthrough-wrapper">
+    <slot />
+  </Primitive>
+</template>

packages/library/tests/primitive.spec.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest'
 import { h } from 'vue'
 import { mount } from '@vue/test-utils'
 import { Primitive } from '../src/lib/primitive'
+import SlotPassthrough from './fixtures/SlotPassthrough.vue'
 
 describe('Primitive', () => {
   it('renders the "as" tag with forwarded attrs when asChild is false', () => {
@@ -42,4 +43,27 @@ describe('Primitive', () => {
       }),
     ).toThrow()
   })
+
+  it('merges attrs through a real SFC that forwards `<slot />` as asChild content', async () => {
+    // Regression test: `<slot />` used as a passthrough outlet inside an SFC
+    // template resolves through Vue's renderSlot() helper, which wraps the
+    // forwarded content in a Fragment vnode even when there's exactly one
+    // real child. Slot must unwrap that Fragment before cloning, or the
+    // merged attrs silently vanish onto the inert wrapper instead of the
+    // real child element.
+    let clicked = false
+    const wrapper = mount(SlotPassthrough, {
+      props: { asChild: true },
+      attrs: { onClick: () => { clicked = true } },
+      slots: {
+        default: () => h('a', { href: '/somewhere' }, 'Click'),
+      },
+    })
+    const el = wrapper.get('a')
+    expect(el.attributes('data-slot')).toBe('passthrough-wrapper')
+    expect(el.attributes('type')).toBe('button')
+    expect(el.attributes('href')).toBe('/somewhere')
+    await el.trigger('click')
+    expect(clicked).toBe(true)
+  })
 })