fix benchmark return baseline

crates/bt-demo/src/main.rs

@@ -194,17 +194,18 @@ fn write_equity_curve_csv(path: &Path, rows: &[DailyEquityPoint]) -> Result<(),
     let mut file = fs::File::create(path)?;
     writeln!(
         file,
-        "date,cash,market_value,total_equity,benchmark_close,notes,diagnostics"
+        "date,cash,market_value,total_equity,benchmark_close,benchmark_prev_close,notes,diagnostics"
     )?;
     for row in rows {
         writeln!(
             file,
-            "{},{:.2},{:.2},{:.2},{:.2},{},{}",
+            "{},{:.2},{:.2},{:.2},{:.2},{:.2},{},{}",
             row.date,
             row.cash,
             row.market_value,
             row.total_equity,
             row.benchmark_close,
+            row.benchmark_prev_close,
             sanitize_csv_field(&row.notes),
             sanitize_csv_field(&row.diagnostics),
         )?;
@@ -317,6 +318,7 @@ fn build_summary(
                 "marketValue": row.market_value,
                 "totalEquity": row.total_equity,
                 "benchmarkClose": row.benchmark_close,
+                "benchmarkPrevClose": row.benchmark_prev_close,
                 "notes": row.notes,
                 "diagnostics": row.diagnostics,
             })