feat(decodes): say when the decoder's band is not the rig's

A decoding application that loses its CAT link keeps announcing the last
dial frequency it knew, and every decode after that carries a stale
band. Nothing downstream can tell: the entity verdicts, the band filter
and the FT map all believe it. Seen for real — MSHV kept saying 80 m,
and Korea read as a NEW BAND because on 80 m it would have been.

Said, not decided. Taking the rig's band instead would be wrong for
anyone decoding a second receiver on another band, and a warning costs
that setup nothing but a line to read past. Shown only while CAT is
actually connected: an empty band means there is nothing to compare
with, never that the rig is on no band. Opens 0.27.9.

frontend/src/components/DecodesPanel.tsx

@@ -13,7 +13,7 @@
 // come from the same resolver the cluster uses, so a call means the same thing in
 // both panels rather than being judged twice by two rules.
 import { useEffect, useMemo, useState } from 'react';
-import { Radio, Search, X, Signal, ArrowUpRight, Timer, Trash2, Ban, Columns2, Bot } from 'lucide-react';
+import { AlertTriangle, Radio, Search, X, Signal, ArrowUpRight, Timer, Trash2, Ban, Columns2, Bot } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { useI18n } from '@/lib/i18n';
 import { chaseAllows } from '@/lib/spotDisplay';
@@ -95,6 +95,9 @@ interface Props {
   // receiver reported last, which is a coin toss — each pane needs its own.
   txStates?: Record<string, TxMsg>;
   spotStatus: Record<string, StatusEntry>;
+  // The band the RIG is on, when CAT is connected. Only ever compared with what
+  // the decoder announces — see the drift warning.
+  rigBand?: string;
   onCall: (d: Decode) => void;
   myCall?: string;
   // Drop every decode and transmit message held for this panel. The list is a
@@ -539,7 +542,7 @@ function buildPeriods(filtered: Decode[], txMsgs: TxMsg[]) {
     }));
 }
 
-export function DecodesPanel({ decodes, txMsgs, txState, txStates, spotStatus, onCall, myCall, onClear, onHalt, autoCallOn, onToggleAutoCall }: Props) {
+export function DecodesPanel({ decodes, txMsgs, txState, txStates, spotStatus, rigBand, onCall, myCall, onClear, onHalt, autoCallOn, onToggleAutoCall }: Props) {
   const { t } = useI18n();
   // Column widths, dragged in the header and shared by every row. Persisted
   // through writeUiPref (not raw localStorage) so the layout travels with data/
@@ -597,6 +600,21 @@ export function DecodesPanel({ decodes, txMsgs, txState, txStates, spotStatus, o
 
   // The mode currently on the air, for the slot clock. The newest decode knows
   // best; between overs the transmit state still does.
+  // A decoder that has lost its CAT link keeps announcing the last dial
+  // frequency it knew, and every decode after that carries a stale band. Nothing
+  // downstream can tell: the entity verdicts, the band filter and the FT map all
+  // believe what the decoder said, and an operator ends up reading NEW BAND for a
+  // band they are not on. (Seen for real: MSHV lost CAT, kept saying 80 m, and
+  // Korea showed as a new band because on 80 m it would have been.)
+  //
+  // Said, not decided. Using the rig's band instead would be wrong for anyone
+  // decoding a second receiver on another band, and a warning costs that setup
+  // nothing but a line it can read past.
+  const decoderBand = decodes.length ? (decodes[decodes.length - 1].band ?? '') : '';
+  const bandDrift = !!rigBand && !!decoderBand
+    && rigBand.toLowerCase() !== decoderBand.toLowerCase();
+  const driftInstance = decodes.length ? (decodes[decodes.length - 1].instance ?? '') : '';
+
   const liveMode = decodes.length ? decodes[decodes.length - 1].mode : txState?.mode;
   const liveTr = trSeconds(liveMode, decodes.length ? decodes[decodes.length - 1].tr_period : undefined);
 
@@ -733,6 +751,18 @@ export function DecodesPanel({ decodes, txMsgs, txState, txStates, spotStatus, o
             what the transmit state reports, so it is right the moment anything
             is heard and keeps running when the band goes quiet. */}
         <PeriodClock trSec={liveTr} mode={liveMode} />
+        {bandDrift && (
+          <span
+            title={t('dec.bandDriftTip')}
+            className="inline-flex items-center gap-1 rounded-full border border-warning px-2 py-0.5 text-[11px] font-semibold text-warning">
+            <AlertTriangle className="size-3.5" />
+            {t('dec.bandDrift', {
+              app: driftInstance || t('dec.bandDriftApp'),
+              dec: decoderBand.toUpperCase(),
+              rig: (rigBand ?? '').toUpperCase(),
+            })}
+          </span>
+        )}
         <span className="w-px h-5 bg-border/60 mx-1" />
 
         <button type="button" className={chip(cqOnly, 'success')} onClick={() => setCqOnly(!cqOnly)}>