What happened?

The CAT-config UI offers a VFO B selector for every port regardless of dialect. But the rigctld (Hamlib) dialect is single-VFO per port — RigctlProtocol has no VFO B concept. Each rigctld port maps to exactly one slice (its RX slice); split is handled create-on-demand (a dedicated TX slice is created when a client issues set_split_vfo 1), not via a pre-configured second VFO.

So a "VFO B" configured for a rigctld port has no effect — the protocol ignores it. Exposing the selector is misleading (it implies an assignment that never takes), and the stored value can be silently clobbered when the port's dialect is toggled. By contrast, the SmartSDR Flex / TS-2000 dialects do support a configured VFO B (dual-VFO operation, e.g. the SmartSDR-for-Mac dual-VFO layout).

What did you expect?

For the rigctld dialect: the VFO B selector forced to "-" and disabled; the operator's saved VFO B preserved (not clobbered) across a dialect switch and restored on switch-back; and settings migration should not seed a VFO B for the default rigctld port.

Steps to reproduce

1. Open CAT config; on a port, choose a dual-VFO dialect (Flex or TS-2000) and set VFO B (e.g. slice B).
2. Switch that port's dialect to Rigctld — the VFO B selector is still offered but has no effect on the single-VFO rigctld port.

Radio model & firmware

N/A — CAT config UI (model-independent)

Operating system

macOS / Linux / Windows (shared GUI code)