Interface ConnectionHandle

Stop listening for host messages. The already-applied .dark class and the data-ispo-theme attribute stay in place — clearing them would cause a flash of mismatched theme, and the project is presumably unmounting anyway.

True when the HOST is an unpackaged dev build, false when packaged, null before a theme frame carried the flag (or under an older host). This is the host build flavor — NOT this project's §3.18 effective bundle mode — so it is stable for the host's whole lifetime. Use it to gate developer-only surfaces (e.g. the Design app's shadcn registry tab).

Most recent theme received, or null before first message.