Changes

• Fixes @astrojs/vue SSR concatenating slot HTML character-by-character when the slot content is large (e.g. an island): Astro hands slots to renderers as a String wrapper object, which Vue's streaming renderer treats as a nested buffer.
• StaticHtml now converts slot content with String() before setting innerHTML, making Vue SSR render it as one string. Output markup is unchanged.

Testing

• Adds test/units/static-html.test.ts verifying slot HTML is rendered as a single string.

Docs

• No docs update needed — no user-facing behavior or markup change.