feat: add usage tracking, output mode, and cli exit mode (#7)

src/cli/components/SessionStats.tsx

@@ -0,0 +1,34 @@
+import { Box, Text } from "ink";
+import type { SessionStatsSnapshot } from "../../agent/stats";
+
+interface SessionStatsProps {
+  stats: SessionStatsSnapshot;
+}
+
+function formatDuration(ms: number): string {
+  if (ms < 1000) {
+    return `${Math.round(ms)}ms`;
+  }
+  return `${(ms / 1000).toFixed(1)}s`;
+}
+
+function formatNumber(n: number): string {
+  return n.toLocaleString();
+}
+
+export function SessionStats({ stats }: SessionStatsProps) {
+  const wallDuration = formatDuration(stats.totalWallMs);
+  const apiDuration = formatDuration(stats.totalApiMs);
+
+  return (
+    <Box flexDirection="column" paddingTop={1}>
+      <Text dimColor>Total duration (API): {apiDuration}</Text>
+      <Text dimColor>Total duration (wall): {wallDuration}</Text>
+      <Text dimColor>
+        Usage: {stats.usage.stepCount} steps,{" "}
+        {formatNumber(stats.usage.promptTokens)} input,{" "}
+        {formatNumber(stats.usage.completionTokens)} output
+      </Text>
+    </Box>
+  );
+}