feat(ui): add ExchangeList compact component for 3-column layout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/pages/Exchanges/ExchangeList.module.css

@@ -0,0 +1,74 @@
+.list {
+  display: flex;
+  flex-direction: column;
+  overflow-y: auto;
+  height: 100%;
+  border-right: 1px solid var(--border);
+  background: var(--surface);
+}
+
+.item {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.625rem 0.75rem;
+  cursor: pointer;
+  border-bottom: 1px solid var(--border-light);
+  font-size: 0.8125rem;
+  transition: background 0.1s;
+}
+
+.item:hover {
+  background: var(--surface-hover);
+}
+
+.itemSelected {
+  background: var(--surface-active);
+  border-left: 3px solid var(--amber);
+  padding-left: calc(0.75rem - 3px);
+}
+
+.dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  flex-shrink: 0;
+}
+
+.dotOk { background: var(--success); }
+.dotErr { background: var(--error); }
+.dotRun { background: var(--running); }
+
+.meta {
+  flex: 1;
+  min-width: 0;
+}
+
+.exchangeId {
+  font-family: var(--font-mono);
+  font-size: 0.6875rem;
+  color: var(--text-muted);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.duration {
+  font-family: var(--font-mono);
+  font-size: 0.75rem;
+  color: var(--text-secondary);
+  flex-shrink: 0;
+}
+
+.timestamp {
+  font-size: 0.6875rem;
+  color: var(--text-muted);
+  flex-shrink: 0;
+}
+
+.empty {
+  padding: 2rem;
+  text-align: center;
+  color: var(--text-muted);
+  font-size: 0.8125rem;
+}

ui/src/pages/Exchanges/ExchangeList.tsx

@@ -0,0 +1,56 @@
+import type { ExecutionSummary } from '../../api/types';
+import styles from './ExchangeList.module.css';
+
+interface ExchangeListProps {
+  exchanges: ExecutionSummary[];
+  selectedId?: string;
+  onSelect: (exchange: ExecutionSummary) => void;
+}
+
+function formatDuration(ms: number): string {
+  if (ms >= 60_000) return `${(ms / 1000).toFixed(0)}s`;
+  if (ms >= 1000) return `${(ms / 1000).toFixed(2)}s`;
+  return `${ms}ms`;
+}
+
+function formatTime(iso: string): string {
+  const d = new Date(iso);
+  const h = String(d.getHours()).padStart(2, '0');
+  const m = String(d.getMinutes()).padStart(2, '0');
+  const s = String(d.getSeconds()).padStart(2, '0');
+  return `${h}:${m}:${s}`;
+}
+
+function dotClass(status: string): string {
+  switch (status) {
+    case 'COMPLETED': return styles.dotOk;
+    case 'FAILED': return styles.dotErr;
+    case 'RUNNING': return styles.dotRun;
+    default: return styles.dotOk;
+  }
+}
+
+export function ExchangeList({ exchanges, selectedId, onSelect }: ExchangeListProps) {
+  if (exchanges.length === 0) {
+    return <div className={styles.empty}>No exchanges found</div>;
+  }
+
+  return (
+    <div className={styles.list}>
+      {exchanges.map((ex) => (
+        <div
+          key={ex.executionId}
+          className={`${styles.item} ${selectedId === ex.executionId ? styles.itemSelected : ''}`}
+          onClick={() => onSelect(ex)}
+        >
+          <span className={`${styles.dot} ${dotClass(ex.status)}`} />
+          <div className={styles.meta}>
+            <div className={styles.exchangeId}>{ex.executionId.slice(0, 12)}</div>
+          </div>
+          <span className={styles.duration}>{formatDuration(ex.durationMs)}</span>
+          <span className={styles.timestamp}>{formatTime(ex.startTime)}</span>
+        </div>
+      ))}
+    </div>
+  );
+}