Add trade ledger debugging exercise

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.py

@@ -0,0 +1,41 @@
+import sys
+
+from ledger import Ledger, Trade
+from logger import BufferedLogger
+
+BLOTTER = [
+    Trade("T1", "AAPL", "BUY", 100, 190.00),
+    Trade("T2", "AAPL", "BUY", 50, 196.00),
+    Trade("T3", "MSFT", "BUY", 200, 410.00),
+    Trade("T4", "AAPL", "SELL", 120, 199.50),
+    Trade("T5", "MSFT", "SELL", 0, 412.00),
+    Trade("T6", "AAPL", "SELL", 80, 201.00),
+    Trade("T7", "IBM", "SELL", 30, 225.00),
+]
+
+
+def main():
+    live_log = BufferedLogger("live", level="INFO", stream=sys.stdout)
+    live = Ledger(live_log)
+    for trade in BLOTTER:
+        try:
+            live.apply(trade)
+        except ValueError:
+            pass
+    live_log.flush()
+
+    eod_log = BufferedLogger("eod", level="INFO", stream=sys.stdout)
+    eod = Ledger.rebuild(live.history, eod_log)
+    eod_log.flush()
+
+    print()
+    for symbol in sorted(live.positions):
+        p = live.positions[symbol]
+        print(f"{symbol:<5} qty={p.qty:>5} avg={p.avg_price:>9.4f} realized={p.realized:>10.2f}")
+
+    breaks = live.reconcile(eod)
+    print("reconcile:", "OK" if not breaks else breaks)
+
+
+if __name__ == "__main__":
+    main()