diff --git a/src/trx-server/src/rig_task.rs b/src/trx-server/src/rig_task.rs
index 358606b..26df369 100644
--- a/src/trx-server/src/rig_task.rs
+++ b/src/trx-server/src/rig_task.rs
@@ -1400,4 +1400,298 @@ mod tests {
         assert_eq!(state.reset_seqs.ft2_decode_reset_seq, 7);
         assert_eq!(state.reset_seqs.wspr_decode_reset_seq, 8);
     }
+
+    #[test]
+    fn usb_freq_change_invalidates_ftx_and_wspr_only() {
+        let mut state = RigState::new_uninitialized();
+        state.apply_mode(RigMode::USB);
+        let prev_freq_hz = state.status.freq.hz;
+        state.apply_freq(Freq {
+            hz: prev_freq_hz + 1_500,
+        });
+
+        invalidate_main_decoder_windows_on_freq_change(&mut state, prev_freq_hz);
+
+        // No effect on PKT, HF-APRS, CW.
+        assert_eq!(state.reset_seqs.aprs_decode_reset_seq, 0);
+        assert_eq!(state.reset_seqs.hf_aprs_decode_reset_seq, 0);
+        assert_eq!(state.reset_seqs.cw_decode_reset_seq, 0);
+        // FT8/FT4/FT2/WSPR all bumped.
+        assert_eq!(state.reset_seqs.ft8_decode_reset_seq, 1);
+        assert_eq!(state.reset_seqs.ft4_decode_reset_seq, 1);
+        assert_eq!(state.reset_seqs.ft2_decode_reset_seq, 1);
+        assert_eq!(state.reset_seqs.wspr_decode_reset_seq, 1);
+    }
+
+    #[test]
+    fn cw_freq_change_invalidates_cw_only() {
+        for mode in [RigMode::CW, RigMode::CWR] {
+            let mut state = RigState::new_uninitialized();
+            state.apply_mode(mode.clone());
+            let prev_freq_hz = state.status.freq.hz;
+            state.apply_freq(Freq {
+                hz: prev_freq_hz + 100,
+            });
+
+            invalidate_main_decoder_windows_on_freq_change(&mut state, prev_freq_hz);
+
+            assert_eq!(state.reset_seqs.cw_decode_reset_seq, 1, "mode={:?}", mode);
+            assert_eq!(state.reset_seqs.aprs_decode_reset_seq, 0);
+            assert_eq!(state.reset_seqs.hf_aprs_decode_reset_seq, 0);
+            assert_eq!(state.reset_seqs.ft8_decode_reset_seq, 0);
+            assert_eq!(state.reset_seqs.ft4_decode_reset_seq, 0);
+            assert_eq!(state.reset_seqs.ft2_decode_reset_seq, 0);
+            assert_eq!(state.reset_seqs.wspr_decode_reset_seq, 0);
+        }
+    }
+
+    #[test]
+    fn am_lsb_fm_freq_change_does_not_touch_main_decoders() {
+        // Modes the freq-change table intentionally ignores: any change leaves
+        // every decoder reset_seq untouched.
+        for mode in [RigMode::AM, RigMode::LSB, RigMode::FM, RigMode::SAM] {
+            let mut state = RigState::new_uninitialized();
+            state.apply_mode(mode.clone());
+            state.reset_seqs.cw_decode_reset_seq = 99;
+            state.reset_seqs.ft8_decode_reset_seq = 99;
+            let prev_freq_hz = state.status.freq.hz;
+            state.apply_freq(Freq {
+                hz: prev_freq_hz + 5_000,
+            });
+
+            invalidate_main_decoder_windows_on_freq_change(&mut state, prev_freq_hz);
+
+            assert_eq!(state.reset_seqs.cw_decode_reset_seq, 99, "mode={:?}", mode);
+            assert_eq!(state.reset_seqs.ft8_decode_reset_seq, 99, "mode={:?}", mode);
+        }
+    }
+
+    #[test]
+    fn map_signal_strength_uses_fm_offset_for_fm_modes() {
+        // FM-family modes start at -120 dBm at raw=0; +6 dBm per raw step.
+        for mode in [RigMode::FM, RigMode::WFM, RigMode::AIS, RigMode::VDES] {
+            assert_eq!(map_signal_strength(&mode, 0), -120.0, "mode={:?}", mode);
+            assert_eq!(map_signal_strength(&mode, 5), -90.0, "mode={:?}", mode);
+            assert_eq!(map_signal_strength(&mode, 15), -30.0, "mode={:?}", mode);
+        }
+    }
+
+    #[test]
+    fn map_signal_strength_uses_default_offset_for_ssb_and_cw() {
+        // Everything else starts at -127 dBm at raw=0.
+        for mode in [
+            RigMode::USB,
+            RigMode::LSB,
+            RigMode::CW,
+            RigMode::CWR,
+            RigMode::AM,
+            RigMode::SAM,
+            RigMode::DIG,
+            RigMode::PKT,
+        ] {
+            assert_eq!(map_signal_strength(&mode, 0), -127.0, "mode={:?}", mode);
+            assert_eq!(map_signal_strength(&mode, 1), -121.0, "mode={:?}", mode);
+            assert_eq!(map_signal_strength(&mode, 15), -37.0, "mode={:?}", mode);
+        }
+    }
+
+    #[test]
+    fn lock_state_falls_back_to_status_when_no_control_override() {
+        let mut state = RigState::new_uninitialized();
+        state.control.lock = None;
+        state.status.lock = Some(true);
+        assert!(lock_state_from(&state));
+        state.status.lock = Some(false);
+        assert!(!lock_state_from(&state));
+    }
+
+    #[test]
+    fn lock_state_control_override_takes_precedence() {
+        let mut state = RigState::new_uninitialized();
+        state.control.lock = Some(false);
+        state.status.lock = Some(true);
+        // Control wins over status.
+        assert!(!lock_state_from(&state));
+        state.control.lock = Some(true);
+        state.status.lock = Some(false);
+        assert!(lock_state_from(&state));
+    }
+
+    #[test]
+    fn lock_state_defaults_to_false_when_neither_set() {
+        let mut state = RigState::new_uninitialized();
+        state.control.lock = None;
+        state.status.lock = None;
+        assert!(!lock_state_from(&state));
+    }
+
+    #[test]
+    fn tx_meter_parts_returns_quad_of_nones_when_no_tx_status() {
+        assert_eq!(tx_meter_parts(None), (None, None, None, None));
+    }
+
+    #[test]
+    fn tx_meter_parts_extracts_fields_in_order() {
+        let tx = RigTxStatus {
+            power: Some(50),
+            limit: Some(100),
+            swr: Some(1.5),
+            alc: Some(7),
+        };
+        assert_eq!(
+            tx_meter_parts(Some(&tx)),
+            (Some(50), Some(100), Some(1.5), Some(7))
+        );
+    }
+
+    #[test]
+    fn meters_changed_detects_rx_signal_change() {
+        let mut a = RigState::new_uninitialized();
+        let mut b = a.clone();
+        a.status.rx = Some(RigRxStatus { sig: Some(-90.0) });
+        b.status.rx = Some(RigRxStatus { sig: Some(-50.0) });
+        assert!(meters_changed(&a, &b));
+    }
+
+    #[test]
+    fn meters_changed_detects_tx_power_change() {
+        let mut a = RigState::new_uninitialized();
+        let mut b = a.clone();
+        a.status.tx = Some(RigTxStatus {
+            power: Some(10),
+            limit: None,
+            swr: None,
+            alc: None,
+        });
+        b.status.tx = Some(RigTxStatus {
+            power: Some(80),
+            limit: None,
+            swr: None,
+            alc: None,
+        });
+        assert!(meters_changed(&a, &b));
+    }
+
+    #[test]
+    fn meters_changed_false_when_unchanged() {
+        let mut a = RigState::new_uninitialized();
+        a.status.rx = Some(RigRxStatus { sig: Some(-70.0) });
+        a.status.tx = Some(RigTxStatus {
+            power: Some(25),
+            limit: Some(100),
+            swr: Some(1.2),
+            alc: None,
+        });
+        let b = a.clone();
+        assert!(!meters_changed(&a, &b));
+    }
+
+    fn sample_rig_info() -> trx_core::rig::RigInfo {
+        use trx_core::radio::freq::Band;
+        use trx_core::rig::{RigAccessMethod, RigCapabilities, RigInfo};
+        RigInfo {
+            manufacturer: "Test".into(),
+            model: "Dummy".into(),
+            revision: "0".into(),
+            capabilities: RigCapabilities {
+                min_freq_step_hz: 1,
+                supported_bands: vec![Band {
+                    low_hz: 7_000_000,
+                    high_hz: 7_200_000,
+                    tx_allowed: true,
+                }],
+                supported_modes: vec![RigMode::USB],
+                num_vfos: 1,
+                lock: false,
+                lockable: true,
+                attenuator: false,
+                preamp: false,
+                rit: false,
+                rpt: false,
+                split: false,
+                tx: true,
+                tx_limit: false,
+                vfo_switch: false,
+                filter_controls: false,
+                signal_meter: true,
+            },
+            access: RigAccessMethod::Tcp {
+                addr: "127.0.0.1:0".into(),
+            },
+        }
+    }
+
+    #[test]
+    fn desired_machine_state_disconnected_when_no_rig_info() {
+        let state = RigState::new_uninitialized();
+        assert!(state.rig_info.is_none());
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::Disconnected
+        ));
+    }
+
+    #[test]
+    fn desired_machine_state_initializing_when_rig_info_but_not_initialized() {
+        let mut state = RigState::new_uninitialized();
+        state.rig_info = Some(sample_rig_info());
+        // initialized stays false.
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::Initializing { rig_info: Some(_) }
+        ));
+    }
+
+    #[test]
+    fn desired_machine_state_powered_off_when_control_disabled() {
+        let mut state = RigState::new_uninitialized();
+        state.rig_info = Some(sample_rig_info());
+        state.initialized = true;
+        state.control.enabled = Some(false);
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::PoweredOff { .. }
+        ));
+    }
+
+    #[test]
+    fn desired_machine_state_ready_when_initialized_and_not_transmitting() {
+        let mut state = RigState::new_uninitialized();
+        state.rig_info = Some(sample_rig_info());
+        state.initialized = true;
+        // Default control.enabled is Some(false) → PoweredOff. Lift it to make
+        // the ready path observable.
+        state.control.enabled = Some(true);
+        state.status.tx_en = false;
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::Ready(_)
+        ));
+    }
+
+    #[test]
+    fn desired_machine_state_transmitting_when_tx_en() {
+        let mut state = RigState::new_uninitialized();
+        state.rig_info = Some(sample_rig_info());
+        state.initialized = true;
+        state.control.enabled = Some(true);
+        state.status.tx_en = true;
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::Transmitting(_)
+        ));
+    }
+
+    #[test]
+    fn desired_machine_state_powered_off_is_default_for_initialized_rig() {
+        // Documents the default-Some(false) behaviour of RigControl::enabled.
+        let mut state = RigState::new_uninitialized();
+        state.rig_info = Some(sample_rig_info());
+        state.initialized = true;
+        // control.enabled stays at its default Some(false).
+        assert!(matches!(
+            desired_machine_state(&state),
+            RigMachineState::PoweredOff { .. }
+        ));
+    }
 }