fix(udp): edge-detect the decoder's DX Call stream

WSJT-X restates the same DX Call in every Status packet, and a spot clicked
in OpsLog put that call into the last-UDP memory (deliberately, for another
case) — so the guard let the decoder's next restatement straight through and
the entry snapped back to old news. The decoder's stream now only counts when
its value CHANGES; a clear over there resets the edge so re-selecting the
same station still lands. Explicit picks (N1MM, remote, spot relays) are
untouched.

changelog.json

@@ -6,13 +6,15 @@
       "Bulk operations work on any size of selection — setting a field, fixing frequencies, deleting, marking uploads and exporting the selection all failed with “too many SQL variables” past a few tens of thousands of QSOs. Statements are now issued in slices.",
       "Elecraft console: the power meter reads in real watts. The K3’s bargraph is relative to a range that flips at 12 W — calibrated against a real radio’s full table, the PC setting picks the range and the bar converts to watts.",
       "Watchlist: a visual pass toward DXHunter’s look — pink callsigns, counter pills, quieter cards with a hover, the ⚡ back on the DXpedition badge.",
-      "WSJT-X / JTDX: OpsLog can highlight decodes in the decoder’s own Band Activity window from your log — watchlist members pink, new DXCC green, new band orange (option in Settings → Connections). And a freshly-started decoder is asked to replay its on-screen decodes, so the FT decodes panel starts full."
+      "WSJT-X / JTDX: OpsLog can highlight decodes in the decoder’s own Band Activity window from your log — watchlist members pink, new DXCC green, new band orange (option in Settings → Connections). And a freshly-started decoder is asked to replay its on-screen decodes, so the FT decodes panel starts full.",
+      "WSJT-X / JTDX / MSHV: only a CHANGED DX Call updates the entry — the decoder re-broadcasts the same call endlessly, and it kept overwriting a spot clicked in OpsLog."
     ],
     "fr": [
       "Les opérations groupées fonctionnent quelle que soit la taille de la sélection — définir un champ, corriger des fréquences, supprimer, marquer les uploads et exporter la sélection échouaient avec « too many SQL variables » au-delà de quelques dizaines de milliers de QSO. Les requêtes sont désormais émises par tranches.",
       "Console Elecraft : le wattmètre lit en vrais watts. Le bargraph du K3 est relatif à une gamme qui bascule à 12 W — calibré sur la table complète d’une vraie radio, le réglage PC choisit la gamme et la barre se convertit en watts.",
       "Watchlist : une passe visuelle vers le look DXHunter — indicatifs roses, compteurs en pastilles, cartes plus feutrées avec survol, le ⚡ de retour sur le badge DXpedition.",
-      "WSJT-X / JTDX : OpsLog peut surligner les décodages dans la fenêtre Band Activity du décodeur selon votre log — watchlist en rose, nouveau DXCC en vert, nouvelle bande en orange (option dans Réglages → Connections). Et un décodeur fraîchement détecté rejoue ses décodages à l’écran, donc le panneau FT decodes démarre plein."
+      "WSJT-X / JTDX : OpsLog peut surligner les décodages dans la fenêtre Band Activity du décodeur selon votre log — watchlist en rose, nouveau DXCC en vert, nouvelle bande en orange (option dans Réglages → Connections). Et un décodeur fraîchement détecté rejoue ses décodages à l’écran, donc le panneau FT decodes démarre plein.",
+      "WSJT-X / JTDX / MSHV : seul un DX Call qui CHANGE met à jour la saisie — le décodeur rediffuse le même call sans fin, et il écrasait un spot cliqué dans OpsLog."
     ]
   },
   {

frontend/src/App.tsx

@@ -2667,6 +2667,11 @@ export default function App() {
   // "the field still shows the previous broadcast" (safe to update) from "the
   // user has typed a different call" (must not clobber).
   const lastUdpCallRef = useRef('');
+  // Edge detection for the DECODER'S stream: WSJT-X/JTDX/MSHV re-broadcast the
+  // same DX Call in every Status packet, seconds apart, forever. Applying each
+  // one meant a spot clicked in OpsLog was overwritten moments later by the
+  // decoder restating old news. Only a CHANGE in this stream is an event.
+  const lastWsjtEdgeRef = useRef('');
 
   // When the entered callsign turns out to be worked-before, jump to the
   // Worked-before tab so the history is front-and-centre. Only once per call,
@@ -3796,6 +3801,13 @@ export default function App() {
       // Anything that isn't WSJT-X (N1MM, ADIF, a panadapter/cluster click relayed
       // over UDP…) is an explicit pick → force it over an existing call.
       const force = String(p?.service ?? '').toLowerCase() !== 'wsjt';
+      if (!force) {
+        // The decoder's stream: same value as last time = no edge = no update.
+        // Only a changed DX Call is the operator doing something over there.
+        const upper = String(p?.call ?? '').trim().toUpperCase();
+        if (upper && upper === lastWsjtEdgeRef.current) return;
+        lastWsjtEdgeRef.current = upper;
+      }
       // External app moved to a new station → fresh recording for the new target.
       if (applyUdpCall(p?.call, force)) restartRecordingForNewTarget(String(p?.call ?? ''));
     });
@@ -3806,6 +3818,9 @@ export default function App() {
     // Only when something is actually in the entry, so an idle digital app doesn't
     // wipe a call being typed by hand.
     const unsubClear = EventsOn('udp:clear_call', () => {
+      // The decoder cleared its DX Call: the next call it announces — even the
+      // same one re-selected — is a fresh edge.
+      lastWsjtEdgeRef.current = '';
       if (callsignRef.current?.value?.trim() || callsign.trim()) resetEntry();
     });
     // Clicked one of OpsLog's spots on the FlexRadio panadapter → fill the call