fix(backtest): give each sweep started without a run_id its own run (#1549)

- the stamped run directory is claimed atomically; a second sweep in the same second takes the next suffix instead of resuming the first

tests/test_backtest.py

@@ -155,6 +155,23 @@ def test_the_analyst_set_under_test_is_the_one_that_runs(tmp_path):
     assert _FakeGraph.instances[-1].analysts == ["market", "news"]
 
 
+@pytest.mark.unit
+def test_sweeps_started_in_the_same_second_get_their_own_runs(tmp_path, monkeypatch):
+    import tradingagents.backtest as backtest
+
+    class _Frozen(backtest.datetime):
+        @classmethod
+        def now(cls, tz=None):
+            return cls(2026, 1, 20, 9, 30, 0)
+
+    monkeypatch.setattr(backtest, "datetime", _Frozen)
+    first = run_backtest(["NVDA"], ["2026-01-05"], _config(tmp_path))
+    second = run_backtest(["NVDA"], ["2026-01-05"], _config(tmp_path))
+
+    assert first.run_id == "20260120_093000" and second.run_id == "20260120_093000_2"
+    assert first.cells_run == second.cells_run == 1
+
+
 @pytest.mark.unit
 def test_a_run_id_cannot_escape_the_results_directory(tmp_path):
     """run_id becomes a path segment, so it is validated like a ticker is."""

tradingagents/backtest.py

@@ -16,6 +16,7 @@ cell rather than a position carried forward.
 
 from __future__ import annotations
 
+import itertools
 import logging
 from collections.abc import Callable
 from dataclasses import dataclass, field
@@ -126,6 +127,19 @@ class BacktestSummary:
         return "\n".join(lines)
 
 
+def _new_run(runs: Path) -> str:
+    """A new run's id, stamped now, and its directory, claimed so no other sweep shares it."""
+    stamp = datetime.now().strftime("%Y%m%d_%H%M%S")
+    runs.mkdir(parents=True, exist_ok=True)
+    for n in itertools.count(1):
+        run_id = stamp if n == 1 else f"{stamp}_{n}"
+        try:
+            (runs / run_id).mkdir()
+            return run_id
+        except FileExistsError:
+            continue
+
+
 def run_backtest(
     tickers: list[str],
     dates: list[str],
@@ -143,11 +157,15 @@ def run_backtest(
     interrupted sweep resumes by being run again. ``progress(done, total,
     ticker, date)`` is called before each cell that runs.
     """
-    # run_id becomes a path segment, so it is validated like a ticker: an
-    # absolute or dotted value would otherwise place the run outside results_dir.
-    run_id = safe_ticker_component(run_id or datetime.now().strftime("%Y%m%d_%H%M%S"))
-    run_dir = Path(config["results_dir"]) / "backtest" / run_id
-    run_dir.mkdir(parents=True, exist_ok=True)
+    runs = Path(config["results_dir"]) / "backtest"
+    if run_id:
+        # run_id becomes a path segment, so it is validated like a ticker: an
+        # absolute or dotted value would otherwise place the run outside results_dir.
+        run_id = safe_ticker_component(run_id)
+        (runs / run_id).mkdir(parents=True, exist_ok=True)
+    else:
+        run_id = _new_run(runs)
+    run_dir = runs / run_id
     run_config = {**config, "results_dir": str(run_dir),
                   "memory_log_path": str(run_dir / "trading_memory.md")}