Legacy reactive statements are not allowed in components using runes – mixing $: with $state in Svelte 5

The goal is to migrate a component to Svelte 5’s runes reactivity gradually, keeping existing legacy reactive statements ($:) for parts of the logic that are not yet converted, while using $state, $derived, or $effect for new features.

However, the Svelte 5 compiler emits the error “Legacy reactive statements are not allowed in components using runes” when both syntaxes appear in the same file, blocking a piecemeal approach. It is unclear whether a compiler flag or future release will relax this restriction, or if the only supported path is to extract legacy logic into a separate child component.

• Is there a compiler option to permit legacy $: statements in runes‑mode components for incremental migration?
• Does Svelte provide a built‑in way to isolate legacy reactive logic without creating an extra child component?
• Are there plans to allow coexistence of $: and runes in a future Svelte 5.x release?