fix(dataflows): write cache files whole, through a temp file of their own

- the OHLCV cache and the SEC EDGAR cache go through dataflows.files.replace_file: a reader sees the old file or the new one, and concurrent writers never share a temp file

tests/test_cache_writes.py

@@ -0,0 +1,84 @@
+"""Cache files are replaced whole: a reader never sees a half-written file, and
+concurrent writers (tool calls run in parallel) never share a temp file."""
+
+import os
+from pathlib import Path
+
+import pandas as pd
+import pytest
+
+from tradingagents.dataflows.vendors import sec_edgar
+from tradingagents.dataflows.vendors.yahoo import ohlcv
+
+
+def _recording_replace(monkeypatch):
+    moves = []
+    real = os.replace
+
+    def replace(src, dst):
+        moves.append((Path(src), Path(dst)))
+        real(src, dst)
+
+    monkeypatch.setattr(os, "replace", replace)
+    return moves
+
+
+@pytest.mark.unit
+def test_sec_edgar_writers_never_share_a_temp_file(monkeypatch, tmp_path):
+    monkeypatch.setattr(sec_edgar, "get_config", lambda: {"data_cache_dir": str(tmp_path)})
+    monkeypatch.setattr(sec_edgar, "_fetch_json", lambda url: {"url": url})
+    moves = _recording_replace(monkeypatch)
+
+    sec_edgar._cached_json("https://example/a", "facts.json")
+    (tmp_path / "sec_edgar" / "facts.json").unlink()
+    sec_edgar._cached_json("https://example/a", "facts.json")
+
+    temps = [src for src, _ in moves]
+    assert len(set(temps)) == 2
+    assert all(src.parent == dst.parent for src, dst in moves)
+
+
+@pytest.mark.unit
+def test_the_price_cache_is_replaced_whole(monkeypatch, tmp_path):
+    frame = pd.DataFrame({"Date": pd.bdate_range("2026-01-02", periods=3), "Open": 1.0, "High": 1.0,
+                          "Low": 1.0, "Close": 1.0, "Volume": 1})
+    monkeypatch.setattr(ohlcv, "get_config", lambda: {"data_cache_dir": str(tmp_path)})
+    monkeypatch.setattr(ohlcv.yf, "Ticker", lambda s: type("T", (), {"history": lambda self, **k: frame.set_index("Date")})())
+    moves = _recording_replace(monkeypatch)
+
+    ohlcv.load_ohlcv("AAPL", "2026-01-06")
+
+    assert [dst.name for _, dst in moves] == ["AAPL-YFin-data.csv"]
+    assert moves[0][0].parent == tmp_path and moves[0][0] != moves[0][1]
+    assert not list(tmp_path.glob("*.tmp*"))
+
+
+@pytest.mark.unit
+def test_a_replaced_file_keeps_the_usual_permissions(tmp_path):
+    from tradingagents.dataflows.files import replace_file
+
+    plain = tmp_path / "plain.txt"
+    plain.write_text("x")
+    replaced = tmp_path / "replaced.txt"
+    replace_file(replaced, lambda temp: Path(temp).write_text("x"))
+
+    assert replaced.stat().st_mode & 0o777 == plain.stat().st_mode & 0o777
+
+
+@pytest.mark.unit
+def test_a_file_held_open_elsewhere_keeps_its_old_content(monkeypatch, tmp_path):
+    """On Windows a file another reader has open cannot be replaced; the cache
+    write is skipped rather than failing the call that produced the data."""
+    from tradingagents.dataflows import files
+
+    target = tmp_path / "cache.csv"
+    target.write_text("old")
+
+    def locked(src, dst):
+        raise PermissionError("in use")
+
+    monkeypatch.setattr(files.os, "replace", locked)
+    files.replace_file(target, lambda temp: Path(temp).write_text("new"))
+
+    assert target.read_text() == "old"
+    assert list(tmp_path.iterdir()) == [target]