ui: default damped_spring, remove Random option

frontend/src/components/ComparePane.tsx

@@ -51,11 +51,11 @@ export function ComparePane(): JSX.Element {
   const [maxTurns, setMaxTurns] = useState<number>(8);
   const [temperature, setTemperature] = useState<number>(0.4);
 
-  // The system catalogue is fetched separately by each runner; one of
-  // them is enough to populate the selector. We pick `a` arbitrarily.
+  // Default to damped_spring; fall back to first in list.
   useEffect(() => {
     if (!systemId && runner.a.state.systems && runner.a.state.systems.length > 0) {
-      setSystemId(runner.a.state.systems[0]?.system_id ?? "");
+      const preferred = runner.a.state.systems.find((s) => s.system_id === "damped_spring");
+      setSystemId(preferred?.system_id ?? runner.a.state.systems[0]?.system_id ?? "");
     }
   }, [runner.a.state.systems, systemId]);
 
@@ -73,7 +73,7 @@ export function ComparePane(): JSX.Element {
 
   function handleStart(): void {
     void runner.startBoth({
-      systemId: systemId || undefined,
+      systemId: systemId,
       maxTurns,
       connectionA,
       connectionB,
@@ -203,14 +203,11 @@ function CompareControlBar({
             {systems === null ? (
               <option value="">Loading…</option>
             ) : (
-              <>
-                <option value="">Random</option>
-                {systems.map((descriptor) => (
-                  <option key={descriptor.system_id} value={descriptor.system_id}>
-                    {prettySystemId(descriptor.system_id)}
-                  </option>
-                ))}
-              </>
+              systems.map((descriptor) => (
+                <option key={descriptor.system_id} value={descriptor.system_id}>
+                  {prettySystemId(descriptor.system_id)}
+                </option>
+              ))
             )}
           </select>
         </Field>