fix(data): keep future/undated news out of historical windows

The yfinance news date filter only ran when an article had a parsed date, so
flat-format and undated articles bypassed it and leaked future news into
historical/backtest runs. Parse the flat providerPublishTime, apply one
look-ahead-safe window rule across ticker and global news (undated kept only
when the window reaches the present), and return an informative message when
everything is filtered out.

tests/test_news_lookahead.py

@@ -0,0 +1,80 @@
+"""yfinance news must not leak future-dated (or undated, in a backtest) articles
+into a historical window.
+
+Regressions for #992 (flat articles bypassed the date filter), #1007 (global
+news injected future articles), #993 (empty-after-filter returned a blank body).
+"""
+import time
+from datetime import datetime
+from unittest import mock
+
+import pytest
+
+import tradingagents.dataflows.yfinance_news as ynews
+
+
+def _epoch(date_str):
+    return int(time.mktime(datetime.strptime(date_str, "%Y-%m-%d").timetuple()))
+
+
+@pytest.mark.unit
+def test_flat_article_publish_time_is_parsed():
+    # #992: flat articles now carry a pub_date (was always None -> unfilterable).
+    data = ynews._extract_article_data(
+        {"title": "X", "publisher": "P", "link": "l", "providerPublishTime": _epoch("2025-05-09")}
+    )
+    assert data["pub_date"] is not None
+    assert data["pub_date"].strftime("%Y-%m-%d") == "2025-05-09"
+
+
+@pytest.mark.unit
+def test_window_excludes_future_and_undated_in_backtest():
+    start = datetime(2025, 5, 1)
+    end = datetime(2025, 5, 9)  # historical window (well in the past)
+    inside = datetime(2025, 5, 5)
+    future = datetime(2025, 6, 1)
+    assert ynews._in_news_window(inside, start, end) is True
+    assert ynews._in_news_window(future, start, end) is False     # look-ahead blocked
+    assert ynews._in_news_window(None, start, end) is False        # undated -> excluded in backtest
+
+
+@pytest.mark.unit
+def test_window_keeps_undated_in_live_window():
+    # Live window (reaches today): undated articles can't be "future", so keep them.
+    start = datetime.now()
+    end = datetime.now()
+    assert ynews._in_news_window(None, start, end) is True
+
+
+@pytest.mark.unit
+def test_global_news_future_flat_article_excluded(monkeypatch):
+    # #1007: a flat, future-dated global article must not appear in a historical run.
+    future_article = {"title": "FUTURE EVENT", "publisher": "P", "link": "l",
+                      "providerPublishTime": _epoch("2025-06-01")}
+    past_article = {"title": "PAST EVENT", "publisher": "P", "link": "l",
+                    "providerPublishTime": _epoch("2025-05-05")}
+
+    class FakeSearch:
+        def __init__(self, *a, **k):
+            self.news = [future_article, past_article]
+
+    monkeypatch.setattr(ynews.yf, "Search", FakeSearch)
+    out = ynews.get_global_news_yfinance("2025-05-09", look_back_days=7, limit=10)
+    assert "PAST EVENT" in out
+    assert "FUTURE EVENT" not in out  # #1007
+
+
+@pytest.mark.unit
+def test_global_news_empty_after_filter_is_informative(monkeypatch):
+    # #993: everything filtered out -> a clear message, not a blank-bodied report.
+    only_future = {"title": "FUTURE", "publisher": "P", "link": "l",
+                   "providerPublishTime": _epoch("2025-06-01")}
+
+    class FakeSearch:
+        def __init__(self, *a, **k):
+            self.news = [only_future]
+
+    monkeypatch.setattr(ynews.yf, "Search", FakeSearch)
+    out = ynews.get_global_news_yfinance("2025-05-09", look_back_days=7, limit=10)
+    assert "No global news found" in out
+    assert "###" not in out  # no empty article body