fix: cache relay-board drivers so Denkovi/USB-serial boards stay connected

The station-control code rebuilt a fresh driver on every status poll and every
relay set. Stateful boards (Denkovi FTDI D2XX, USB-serial) hold an OS handle only
one opener can own, so the first poll opened the board and leaked the handle, and
every poll after failed with 'device in use' — the relays greyed out a second
after Save and auto-control never switched. Drivers are now cached per device and
reused, closed on config change. Adds a Test-connection button + detect feedback
in the device editor (reported by VK4MA).

app.go

@@ -490,6 +490,8 @@ type App struct {
 	relayAutoMu    sync.Mutex        // serialises relay auto-control evaluation
 	relayAutoLast  map[string]bool   // deviceID|relay → last applied on/off, so we only switch on a real change
 	relayAutoOn    atomic.Bool       // cached "auto-control enabled" so the CAT hot path skips work when off
+	relayDrvMu     sync.Mutex           // guards the cached relay drivers below
+	relayDrv       map[string]cachedRelay // deviceID → live driver (reused across polls; stateful boards can't be reopened per call)
 	pttPort        serial.Port     // open serial port while PTT (RTS/DTR) is asserted
 	pttKeyedMethod string          // "cat" | "rts" | "dtr" while keyed; "" when idle
 	pttGen         int64           // bumped on every key; a delayed unkey only fires if unchanged (guards against a stale release cutting a new transmission)
@@ -11433,8 +11435,15 @@ func relayCountFor(typ string) int {
 	}
 }
 
-// deviceDriver builds the wire driver for a configured device.
-func deviceDriver(d StationDevice) relaydev.Device {
+// cachedRelay is a live driver plus the config signature it was built from, so a
+// changed device (new COM port, serial or channel count) rebuilds it.
+type cachedRelay struct {
+	key string
+	dev relaydev.Device
+}
+
+// buildDeviceDriver builds a fresh wire driver for a configured device.
+func buildDeviceDriver(d StationDevice) relaydev.Device {
 	switch d.Type {
 	case "kmtronic":
 		return relaydev.NewKMTronic(d.Host, d.User, d.Pass)
@@ -11449,12 +11458,74 @@ func deviceDriver(d StationDevice) relaydev.Device {
 	}
 }
 
+// deviceKey is the config signature that, when unchanged, lets us reuse a device's
+// open driver (and its OS handle) instead of rebuilding it every poll.
+func deviceKey(d StationDevice) string {
+	return fmt.Sprintf("%s|%s|%s|%s|%d", d.Type, d.Host, d.User, d.Pass, deviceRelayCount(d))
+}
+
+// driverFor returns the cached, still-open driver for a device, building it once
+// and reusing it thereafter. Stateful boards (Denkovi FTDI, USB-serial) hold an OS
+// handle that only one opener can own, so rebuilding a driver every call — as the
+// old code did — leaked the handle and made every poll after the first fail with
+// "device in use", greying the relays out. Reuse fixes that.
+func (a *App) driverFor(d StationDevice) relaydev.Device {
+	key := deviceKey(d)
+	a.relayDrvMu.Lock()
+	defer a.relayDrvMu.Unlock()
+	if a.relayDrv == nil {
+		a.relayDrv = map[string]cachedRelay{}
+	}
+	if c, ok := a.relayDrv[d.ID]; ok {
+		if c.key == key {
+			return c.dev
+		}
+		_ = c.dev.Close() // config changed → release the old handle before rebuilding
+		delete(a.relayDrv, d.ID)
+	}
+	dev := buildDeviceDriver(d)
+	a.relayDrv[d.ID] = cachedRelay{key: key, dev: dev}
+	return dev
+}
+
+// closeRelayDrivers closes and drops every cached driver (e.g. after the device
+// list changes) so stale handles are released and rebuilt fresh on next use.
+func (a *App) closeRelayDrivers() {
+	a.relayDrvMu.Lock()
+	defer a.relayDrvMu.Unlock()
+	for id, c := range a.relayDrv {
+		_ = c.dev.Close()
+		delete(a.relayDrv, id)
+	}
+}
+
 // ListDenkoviDevices returns the FTDI serial numbers of connected Denkovi/FTDI
 // boards, for the settings picker. Windows-only (FTDI D2XX).
 func (a *App) ListDenkoviDevices() ([]string, error) {
 	return relaydev.ListDenkovi()
 }
 
+// StationTestResult is the outcome of probing one relay board, for the settings
+// dialog's Connect/Test button so the user gets a clear connected/failed message.
+type StationTestResult struct {
+	OK     bool   `json:"ok"`
+	Relays int    `json:"relays"`
+	Error  string `json:"error,omitempty"`
+}
+
+// TestStationDevice opens the given board and reads its state, returning a clear
+// success/failure so the settings UI can tell the user whether it's reachable.
+// Reuses the cached driver (no double-open conflict with the live poll).
+func (a *App) TestStationDevice(d StationDevice) StationTestResult {
+	ctx, cancel := context.WithTimeout(a.ctx, 6*time.Second)
+	defer cancel()
+	states, err := a.driverFor(d).Status(ctx)
+	if err != nil {
+		return StationTestResult{OK: false, Error: err.Error()}
+	}
+	return StationTestResult{OK: true, Relays: len(states)}
+}
+
 // GetStationDevices returns the configured relay boards (without live state).
 func (a *App) GetStationDevices() []StationDevice {
 	out := []StationDevice{}
@@ -11497,6 +11568,9 @@ func (a *App) SaveStationDevices(devs []StationDevice) error {
 	if err != nil {
 		return err
 	}
+	// Release any open board handles so the new config reopens cleanly (a changed
+	// COM port / FTDI serial must not stay held by a stale driver).
+	a.closeRelayDrivers()
 	return a.settings.SetGlobal(a.ctx, keyStationDevices, string(b))
 }
 
@@ -11532,7 +11606,7 @@ func (a *App) GetStationStatus() []StationDeviceStatus {
 			ds := StationDeviceStatus{ID: d.ID, Name: d.Name, Type: d.Type}
 			ctx, cancel := context.WithTimeout(a.ctx, 6*time.Second)
 			defer cancel()
-			states, err := deviceDriver(d).Status(ctx)
+			states, err := a.driverFor(d).Status(ctx)
 			if err != nil {
 				ds.Error = err.Error()
 			} else {
@@ -11563,7 +11637,7 @@ func (a *App) StationSetRelay(id string, relay int, on bool) error {
 		if d.ID == id {
 			ctx, cancel := context.WithTimeout(a.ctx, 6*time.Second)
 			defer cancel()
-			return deviceDriver(d).Set(ctx, relay, on)
+			return a.driverFor(d).Set(ctx, relay, on)
 		}
 	}
 	return fmt.Errorf("station device %q not found", id)

frontend/src/components/StationControlPanel.tsx

@@ -12,7 +12,7 @@ import {
   GetStationDevices, SaveStationDevices, GetStationStatus, StationSetRelay,
   GetRotatorHeading, RotatorGoTo, RotatorStop,
   GetUltrabeamStatus, SetUltrabeamDirection, UltrabeamRetract, MotorSetElement, MotorReadElements,
-  ListDenkoviDevices, ListSerialPorts,
+  ListDenkoviDevices, ListSerialPorts, TestStationDevice,
 } from '../../wailsjs/go/main/App';
 
 type RotatorProps = { centerLat?: number | null; centerLon?: number | null; bearing?: number | null };
@@ -473,16 +473,33 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
   // Detected FTDI serials for the Denkovi picker.
   const [denkoviSerials, setDenkoviSerials] = useState<string[]>([]);
   const [detecting, setDetecting] = useState(false);
+  const [detectMsg, setDetectMsg] = useState('');
   const detectDenkovi = async () => {
     setDetecting(true);
+    setDetectMsg('');
     try {
       const list = ((await ListDenkoviDevices()) ?? []) as string[];
       setDenkoviSerials(list);
       // Auto-fill when there's exactly one and nothing chosen yet.
       if (list.length >= 1 && !device.host.trim()) onChange({ ...device, host: list[0] });
-    } catch { setDenkoviSerials([]); }
+      setDetectMsg(list.length === 0 ? t('station.detectNone') : t('station.detectFound', { n: list.length }));
+    } catch (e: any) { setDenkoviSerials([]); setDetectMsg(String(e?.message || e || t('station.detectNone'))); }
     finally { setDetecting(false); }
   };
+  // Connection test result for the current device config.
+  const [testing, setTesting] = useState(false);
+  const [testMsg, setTestMsg] = useState<{ ok: boolean; text: string } | null>(null);
+  const testDevice = async () => {
+    setTesting(true);
+    setTestMsg(null);
+    try {
+      const r: any = await TestStationDevice(device as any);
+      setTestMsg(r?.ok
+        ? { ok: true, text: t('station.testOk', { n: r.relays }) }
+        : { ok: false, text: r?.error || t('station.testFail') });
+    } catch (e: any) { setTestMsg({ ok: false, text: String(e?.message || e || t('station.testFail')) }); }
+    finally { setTesting(false); }
+  };
   useEffect(() => { if (isDenkovi) void detectDenkovi(); /* eslint-disable-next-line */ }, [isDenkovi]);
   return (
     <div ref={ref} className="mt-4 max-w-4xl rounded-xl border border-primary/40 bg-card p-4 space-y-3">
@@ -534,6 +551,7 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
             </Button>
           </div>
           <p className="text-[10px] text-muted-foreground">{t('station.ftdiHint')}</p>
+          {detectMsg && <p className="text-[11px] font-medium text-muted-foreground">{detectMsg}</p>}
         </div>
       ) : isUsbRelay ? (
         <div className="space-y-1 max-w-md">
@@ -581,9 +599,21 @@ function DeviceEditor({ device, onChange, onSave, onCancel, t }: {
           ))}
         </div>
       </div>
-      <div className="flex justify-end gap-2">
-        <Button size="sm" variant="ghost" onClick={onCancel}><X className="size-3.5 mr-1" />{t('station.cancel')}</Button>
-        <Button size="sm" onClick={onSave} disabled={!device.host.trim()}><Check className="size-3.5 mr-1" />{t('station.save')}</Button>
+      <div className="flex items-center gap-2">
+        {testMsg && (
+          <span className={cn('inline-flex items-center gap-1.5 text-xs font-medium', testMsg.ok ? 'text-success' : 'text-danger')}>
+            <span className={cn('size-2 rounded-full', testMsg.ok ? 'bg-success' : 'bg-danger')} />
+            {testMsg.text}
+          </span>
+        )}
+        <div className="ml-auto flex gap-2">
+          <Button size="sm" variant="outline" onClick={testDevice} disabled={testing || !device.host.trim()}>
+            {testing ? <Loader2 className="size-3.5 mr-1 animate-spin" /> : <PlugZap className="size-3.5 mr-1" />}
+            {t('station.test')}
+          </Button>
+          <Button size="sm" variant="ghost" onClick={onCancel}><X className="size-3.5 mr-1" />{t('station.cancel')}</Button>
+          <Button size="sm" onClick={onSave} disabled={!device.host.trim()}><Check className="size-3.5 mr-1" />{t('station.save')}</Button>
+        </div>
       </div>
     </div>
   );

frontend/src/lib/i18n.tsx

@@ -131,7 +131,7 @@ const en: Dict = {
   'uscty.backfillIntro': 'Resolve county (and grid) for US QSOs already in your log that are missing them. Existing values are kept — only blanks are filled.',
   'uscty.backfillRun': 'Fill missing counties',
   'uscty.backfillDone': '{s} US QSOs scanned · {c} counties, {g} grids filled.',
-  'station.title': 'Station Control', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'No heading read', 'station.pattern': 'Pattern', 'station.bi': 'Bi', 'station.retract': 'Retract elements', 'station.moving': 'MOVING', 'station.elements': 'Elements (mm)', 'station.read': 'Read', 'station.readLengths': 'Read current element lengths from the controller', 'station.noLengths': 'Lengths unknown — click Read to fetch them from the controller.', 'station.element': 'Element', 'station.reflector': 'Reflector', 'station.driven': 'Driven', 'station.director': 'Dir', 'station.set': 'Set', 'station.elementsHint': 'Each press lengthens/shortens the element by 2 mm (like the physical console). Verify which element responds on your antenna.', 'station.setExactLen': 'Click to type the exact current length (fixes the baseline if the auto-read is off).', 'station.atMax': 'Controller refused — the element is likely at its maximum length for this band, so it can\'t extend further.', 'station.go': 'Go', 'station.stop': 'Stop', 'station.dragHint': 'Drag a widget by its card to reorder. Pick a column count to lay them out in a grid.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Add device', 'station.editDevice': 'Edit device', 'station.empty': 'No relay boards yet. Add a WebSwitch 1216H or a KMTronic 8-relay board to control your station power and accessories.', 'station.online': 'Online', 'station.offline': 'Offline', 'station.edit': 'Edit', 'station.delete': 'Delete', 'station.relay': 'Relay', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': 'Device type', 'station.name': 'Name', 'station.host': 'Host / IP', 'station.user': 'Username', 'station.pass': 'Password', 'station.optional': 'optional', 'station.ftdiSerial': 'FTDI serial number', 'station.detect': 'Detect', 'station.ftdiHint': 'The Denkovi board is driven via FTDI bit-bang (not the COM port). Pick its serial (e.g. DAE0006K). Needs the FTDI D2XX driver installed.', 'station.channels': 'Relays', 'station.comPort': 'COM port', 'station.noPorts': 'No ports found', 'station.usbRelayHint': 'Cheap USB-serial relay boards (CH340/LCUS) using the A0 command protocol. If yours does not switch, tell me its model / command set.', 'station.labels': 'Relay labels', 'station.cancel': 'Cancel', 'station.save': 'Save',
+  'station.title': 'Station Control', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'No heading read', 'station.pattern': 'Pattern', 'station.bi': 'Bi', 'station.retract': 'Retract elements', 'station.moving': 'MOVING', 'station.elements': 'Elements (mm)', 'station.read': 'Read', 'station.readLengths': 'Read current element lengths from the controller', 'station.noLengths': 'Lengths unknown — click Read to fetch them from the controller.', 'station.element': 'Element', 'station.reflector': 'Reflector', 'station.driven': 'Driven', 'station.director': 'Dir', 'station.set': 'Set', 'station.elementsHint': 'Each press lengthens/shortens the element by 2 mm (like the physical console). Verify which element responds on your antenna.', 'station.setExactLen': 'Click to type the exact current length (fixes the baseline if the auto-read is off).', 'station.atMax': 'Controller refused — the element is likely at its maximum length for this band, so it can\'t extend further.', 'station.go': 'Go', 'station.stop': 'Stop', 'station.dragHint': 'Drag a widget by its card to reorder. Pick a column count to lay them out in a grid.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Add device', 'station.editDevice': 'Edit device', 'station.empty': 'No relay boards yet. Add a WebSwitch 1216H or a KMTronic 8-relay board to control your station power and accessories.', 'station.online': 'Online', 'station.offline': 'Offline', 'station.edit': 'Edit', 'station.delete': 'Delete', 'station.relay': 'Relay', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': 'Device type', 'station.name': 'Name', 'station.host': 'Host / IP', 'station.user': 'Username', 'station.pass': 'Password', 'station.optional': 'optional', 'station.ftdiSerial': 'FTDI serial number', 'station.detect': 'Detect', 'station.ftdiHint': 'The Denkovi board is driven via FTDI bit-bang (not the COM port). Pick its serial (e.g. DAE0006K). Needs the FTDI D2XX driver installed.', 'station.channels': 'Relays', 'station.comPort': 'COM port', 'station.noPorts': 'No ports found', 'station.usbRelayHint': 'Cheap USB-serial relay boards (CH340/LCUS) using the A0 command protocol. If yours does not switch, tell me its model / command set.', 'station.labels': 'Relay labels', 'station.cancel': 'Cancel', 'station.save': 'Save', 'station.test': 'Test connection', 'station.testOk': 'Connected — {n} relays', 'station.testFail': 'Not connected', 'station.detectNone': 'No FTDI board found — check the cable and that the D2XX driver is installed.', 'station.detectFound': '{n} board(s) detected.',
   'sec.awards': 'Awards', 'sec.cat': 'CAT interface', 'sec.rotator': 'Rotator', 'sec.winkeyer': 'CW Keyer',
   'sec.antenna': 'Ultrabeam / Steppir', 'sec.antgenius': 'Antenna Genius', 'sec.pgxl': 'Amplifier', 'sec.flex': 'FlexRadio', 'sec.audio': 'Audio devices',
   'sec.relayauto': 'Relay auto-control',
@@ -445,7 +445,7 @@ const fr: Dict = {
   'uscty.backfillIntro': "Résout le comté (et le locator) pour les QSO US déjà dans ton log qui n'en ont pas. Les valeurs existantes sont conservées — seuls les vides sont remplis.",
   'uscty.backfillRun': 'Remplir les comtés manquants',
   'uscty.backfillDone': '{s} QSO US analysés · {c} comtés, {g} locators remplis.',
-  'station.title': 'Contrôle station', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'Azimut non lu', 'station.pattern': 'Diagramme', 'station.bi': 'Bi', 'station.retract': 'Rétracter les éléments', 'station.moving': 'EN MOUVEMENT', 'station.elements': 'Éléments (mm)', 'station.read': 'Lire', 'station.readLengths': 'Lire les longueurs actuelles depuis le contrôleur', 'station.noLengths': 'Longueurs inconnues — clique sur Lire pour les récupérer depuis le contrôleur.', 'station.element': 'Élément', 'station.reflector': 'Réflecteur', 'station.driven': 'Radiateur', 'station.director': 'Dir', 'station.set': 'Régler', 'station.elementsHint': "Chaque appui allonge/raccourcit l'élément de 2 mm (comme le pupitre). Vérifie quel élément répond sur ton antenne.", 'station.setExactLen': "Clique pour taper la longueur actuelle exacte (recale la base si la lecture auto est fausse).", 'station.atMax': "Refusé par le contrôleur — l'élément est probablement en butée (longueur max pour cette bande), il ne peut plus s'allonger.", 'station.go': 'Aller', 'station.stop': 'Stop', 'station.dragHint': 'Glisse une carte pour réordonner. Choisis un nombre de colonnes pour la disposition.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Ajouter un appareil', 'station.editDevice': "Modifier l'appareil", 'station.empty': "Aucune carte relais. Ajoute un WebSwitch 1216H ou une carte KMTronic 8 relais pour piloter l'alimentation et les accessoires de ta station.", 'station.online': 'En ligne', 'station.offline': 'Hors ligne', 'station.edit': 'Modifier', 'station.delete': 'Supprimer', 'station.relay': 'Relais', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': "Type d'appareil", 'station.name': 'Nom', 'station.host': 'Hôte / IP', 'station.user': "Nom d'utilisateur", 'station.pass': 'Mot de passe', 'station.optional': 'optionnel', 'station.ftdiSerial': 'Numéro de série FTDI', 'station.detect': 'Détecter', 'station.ftdiHint': "La carte Denkovi se pilote en FTDI bit-bang (pas via le port COM). Choisis son numéro de série (ex. DAE0006K). Nécessite le driver FTDI D2XX installé.", 'station.channels': 'Relais', 'station.comPort': 'Port COM', 'station.noPorts': 'Aucun port', 'station.usbRelayHint': "Cartes USB-série bon marché (CH340/LCUS) protocole A0. Si la tienne ne commute pas, donne-moi le modèle / jeu de commandes.", 'station.labels': 'Libellés des relais', 'station.cancel': 'Annuler', 'station.save': 'Enregistrer',
+  'station.title': 'Contrôle station', 'station.rotator': 'Rotator', 'station.rotatorNoRead': 'Azimut non lu', 'station.pattern': 'Diagramme', 'station.bi': 'Bi', 'station.retract': 'Rétracter les éléments', 'station.moving': 'EN MOUVEMENT', 'station.elements': 'Éléments (mm)', 'station.read': 'Lire', 'station.readLengths': 'Lire les longueurs actuelles depuis le contrôleur', 'station.noLengths': 'Longueurs inconnues — clique sur Lire pour les récupérer depuis le contrôleur.', 'station.element': 'Élément', 'station.reflector': 'Réflecteur', 'station.driven': 'Radiateur', 'station.director': 'Dir', 'station.set': 'Régler', 'station.elementsHint': "Chaque appui allonge/raccourcit l'élément de 2 mm (comme le pupitre). Vérifie quel élément répond sur ton antenne.", 'station.setExactLen': "Clique pour taper la longueur actuelle exacte (recale la base si la lecture auto est fausse).", 'station.atMax': "Refusé par le contrôleur — l'élément est probablement en butée (longueur max pour cette bande), il ne peut plus s'allonger.", 'station.go': 'Aller', 'station.stop': 'Stop', 'station.dragHint': 'Glisse une carte pour réordonner. Choisis un nombre de colonnes pour la disposition.', 'station.colsAuto': 'Auto', 'station.addDevice': 'Ajouter un appareil', 'station.editDevice': "Modifier l'appareil", 'station.empty': "Aucune carte relais. Ajoute un WebSwitch 1216H ou une carte KMTronic 8 relais pour piloter l'alimentation et les accessoires de ta station.", 'station.online': 'En ligne', 'station.offline': 'Hors ligne', 'station.edit': 'Modifier', 'station.delete': 'Supprimer', 'station.relay': 'Relais', 'station.on': 'ON', 'station.off': 'OFF', 'station.type': "Type d'appareil", 'station.name': 'Nom', 'station.host': 'Hôte / IP', 'station.user': "Nom d'utilisateur", 'station.pass': 'Mot de passe', 'station.optional': 'optionnel', 'station.ftdiSerial': 'Numéro de série FTDI', 'station.detect': 'Détecter', 'station.ftdiHint': "La carte Denkovi se pilote en FTDI bit-bang (pas via le port COM). Choisis son numéro de série (ex. DAE0006K). Nécessite le driver FTDI D2XX installé.", 'station.channels': 'Relais', 'station.comPort': 'Port COM', 'station.noPorts': 'Aucun port', 'station.usbRelayHint': "Cartes USB-série bon marché (CH340/LCUS) protocole A0. Si la tienne ne commute pas, donne-moi le modèle / jeu de commandes.", 'station.labels': 'Libellés des relais', 'station.cancel': 'Annuler', 'station.save': 'Enregistrer', 'station.test': 'Tester la connexion', 'station.testOk': 'Connecté — {n} relais', 'station.testFail': 'Non connecté', 'station.detectNone': 'Aucune carte FTDI trouvée — vérifie le câble et que le driver D2XX est installé.', 'station.detectFound': '{n} carte(s) détectée(s).',
   'sec.awards': 'Diplômes', 'sec.cat': 'Interface CAT', 'sec.rotator': 'Rotator', 'sec.winkeyer': 'Manipulateur CW',
   'sec.antenna': 'Antenne motorisée', 'sec.antgenius': 'Antenna Genius', 'sec.pgxl': 'Amplificateur', 'sec.flex': 'FlexRadio', 'sec.audio': 'Périphériques audio',
   'sec.relayauto': 'Relais automatiques',

frontend/wailsjs/go/main/App.d.ts

@@ -849,6 +849,8 @@ export function TestQRZUpload():Promise<string>;
 
 export function TestRotator(arg1:main.RotatorSettings):Promise<void>;
 
+export function TestStationDevice(arg1:main.StationDevice):Promise<main.StationTestResult>;
+
 export function TestUltrabeam(arg1:main.UltrabeamSettings):Promise<void>;
 
 export function ULSStatus():Promise<main.ULSStatusResult>;

frontend/wailsjs/go/main/App.js

@@ -1654,6 +1654,10 @@ export function TestRotator(arg1) {
   return window['go']['main']['App']['TestRotator'](arg1);
 }
 
+export function TestStationDevice(arg1) {
+  return window['go']['main']['App']['TestStationDevice'](arg1);
+}
+
 export function TestUltrabeam(arg1) {
   return window['go']['main']['App']['TestUltrabeam'](arg1);
 }

frontend/wailsjs/go/models.ts

@@ -2746,6 +2746,22 @@ export namespace main {
 	        this.my_pota_ref = source["my_pota_ref"];
 	    }
 	}
+	export class StationTestResult {
+	    ok: boolean;
+	    relays: number;
+	    error?: string;
+	
+	    static createFrom(source: any = {}) {
+	        return new StationTestResult(source);
+	    }
+	
+	    constructor(source: any = {}) {
+	        if ('string' === typeof source) source = JSON.parse(source);
+	        this.ok = source["ok"];
+	        this.relays = source["relays"];
+	        this.error = source["error"];
+	    }
+	}
 	export class ULSStatusResult {
 	    count: number;
 	    updated_at: string;

internal/relaydev/denkovi_other.go

@@ -20,7 +20,8 @@ func NewDenkovi(serial string, count int) Device {
 	return denkoviStub{count: count}
 }
 
-func (s denkoviStub) Count() int { return s.count }
+func (s denkoviStub) Count() int     { return s.count }
+func (denkoviStub) Close() error     { return nil }
 func (denkoviStub) Status(context.Context) ([]bool, error) {
 	return nil, fmt.Errorf("Denkovi USB relay board is only supported on Windows")
 }

internal/relaydev/denkovi_windows.go

@@ -121,6 +121,19 @@ func (d *denkovi) Set(ctx context.Context, relay int, on bool) error {
 	return d.writeLocked()
 }
 
+// Close releases the FTDI handle so the board can be reopened later (only one
+// handle may hold a D2XX device at a time).
+func (d *denkovi) Close() error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	if d.opened {
+		procClose.Call(d.h)
+		d.opened = false
+		d.h = 0
+	}
+	return nil
+}
+
 func (d *denkovi) Status(ctx context.Context) ([]bool, error) {
 	d.mu.Lock()
 	defer d.mu.Unlock()

internal/relaydev/relaydev.go

@@ -27,6 +27,11 @@ type Device interface {
 	Count() int                                       // number of user-controllable relays
 	Status(ctx context.Context) ([]bool, error)       // state of each relay (index 0 = relay 1)
 	Set(ctx context.Context, relay int, on bool) error // relay is 1-based
+	// Close releases any OS handle the driver holds (serial port, FTDI handle).
+	// Network boards hold nothing and no-op. MUST be called when a cached driver is
+	// discarded so the port/handle is freed for the next open — stateful boards
+	// (Denkovi, USB-serial) can only be opened by one handle at a time.
+	Close() error
 }
 
 func httpClient() *http.Client { return &http.Client{Timeout: 5 * time.Second} }
@@ -62,7 +67,8 @@ type webswitch struct {
 // NewWebswitch builds a WebSwitch 1216H client (5 relays).
 func NewWebswitch(host string) Device { return &webswitch{host: host, count: 5} }
 
-func (w *webswitch) Count() int { return w.count }
+func (w *webswitch) Count() int    { return w.count }
+func (w *webswitch) Close() error  { return nil } // stateless HTTP, nothing to release
 
 func (w *webswitch) Set(ctx context.Context, relay int, on bool) error {
 	if relay < 1 || relay > w.count {
@@ -118,7 +124,8 @@ func NewKMTronic(host, user, pass string) Device {
 	return &kmtronic{host: host, user: user, pass: pass, count: 8}
 }
 
-func (k *kmtronic) Count() int { return k.count }
+func (k *kmtronic) Count() int   { return k.count }
+func (k *kmtronic) Close() error { return nil } // stateless HTTP, nothing to release
 
 func (k *kmtronic) Set(ctx context.Context, relay int, on bool) error {
 	if relay < 1 || relay > k.count {

internal/relaydev/serialrelay.go

@@ -37,6 +37,19 @@ func NewSerialRelay(port string, count int) Device {
 
 func (s *serialRelay) Count() int { return s.count }
 
+// Close releases the COM port so it can be reopened later (only one handle may
+// hold a serial port at a time).
+func (s *serialRelay) Close() error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.port != nil {
+		err := s.port.Close()
+		s.port = nil
+		return err
+	}
+	return nil
+}
+
 func (s *serialRelay) ensureOpen() error {
 	if s.port != nil {
 		return nil