ui(alerts): ExchangeMatchForm — enforce PER_EXCHANGE UI constraints

Disable reNotifyMinutes at 0 with tooltip when PER_EXCHANGE is selected
(server rejects non-zero per Task 3.3 validator). Hide forDurationSeconds
entirely for PER_EXCHANGE (not applicable to per-exchange semantics).
Values stay zeroed via Task 4.3's applyFireModeChange helper on any
mode toggle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Alerts/RuleEditor/TriggerStep.tsx

@@ -17,6 +17,13 @@ export function TriggerStep({
   const { toast } = useToast();
   const [lastResult, setLastResult] = useState<string | null>(null);
 
+  // PER_EXCHANGE fires exactly once per exchange (Task 3.3 server validator
+  // rejects non-zero reNotifyMinutes / forDurationSeconds for this mode).
+  // Gate the two inputs here so users can't type values the server will reject.
+  const isPerExchange =
+    form.conditionKind === 'EXCHANGE_MATCH' &&
+    (form.condition as Record<string, unknown>).fireMode === 'PER_EXCHANGE';
+
   const onTest = async () => {
     if (!ruleId) {
       toast({ title: 'Save rule first to run test evaluate', variant: 'error' });
@@ -40,6 +47,7 @@ export function TriggerStep({
           onChange={(e) => setForm({ ...form, evaluationIntervalSeconds: Number(e.target.value) })}
         />
       </FormField>
+      {!isPerExchange && (
         <FormField label="For-duration before firing (seconds, 0 = fire immediately)">
           <Input
             type="number"
@@ -48,12 +56,19 @@ export function TriggerStep({
             onChange={(e) => setForm({ ...form, forDurationSeconds: Number(e.target.value) })}
           />
         </FormField>
+      )}
       <FormField label="Re-notify cadence (minutes, 0 = notify once)">
         <Input
           type="number"
           min={0}
           value={form.reNotifyMinutes}
           onChange={(e) => setForm({ ...form, reNotifyMinutes: Number(e.target.value) })}
+          disabled={isPerExchange}
+          title={
+            isPerExchange
+              ? 'Per-exchange rules fire exactly once per exchange — re-notify does not apply.'
+              : undefined
+          }
         />
       </FormField>
       <div>