fix(dataflows): report windows a feed cannot observe as unavailable

- Yahoo news and the Reddit and StockTwits feeds serve only recent items, so a
  historical window trimmed to nothing was reported as "no news" or "no
  posts", and the sentiment analyst scored that silence as a neutral signal
- judge each empty window in one shared rule: it is a real absence only when
  the feed's coverage reaches the window's first day and the window ends by
  today; otherwise report it unavailable with where coverage starts
- coverage comes from the returned timestamps, which are newest-first on these
  feeds, plus Reddit's one-week search lookback; merged global-news searches
  prove no continuity and are bounded by the present alone
- state in the sentiment analyst that historical sentiment inputs are not
  guaranteed to be point-in-time

tests/test_news_lookahead.py

@@ -101,5 +101,115 @@ def test_global_news_empty_after_filter_is_informative(monkeypatch):
 
     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
+    # Only a later article came back, so the feed does not reach this window.
+    assert "unavailable" in out and "not an absence" in out
+
+
+
+def _ticker_with(articles, monkeypatch):
+    class FakeTicker:
+        def __init__(self, *a, **k):
+            pass
+
+        def get_news(self, count=20):
+            return articles
+
+    monkeypatch.setattr(ynews.yf, "Ticker", FakeTicker)
+
+
+@pytest.mark.unit
+def test_ticker_news_window_before_feed_coverage_is_unavailable(monkeypatch):
+    # Yahoo serves only recent articles: a historical window gets none of them,
+    # which must read as "cannot answer", not "no news happened".
+    recent = [{"title": "RECENT", "publisher": "P", "link": "l",
+               "providerPublishTime": _epoch("2026-09-10")}]
+    _ticker_with(recent, monkeypatch)
+    out = ynews.get_news_yfinance("AAPL", "2026-08-07", "2026-08-14")
+    assert "RECENT" not in out
+    assert "unavailable" in out and "not an absence" in out
+    assert "2026-09-10" in out  # says how far back the feed actually reaches
+
+
+@pytest.mark.unit
+def test_ticker_news_covered_but_empty_window_is_a_real_absence(monkeypatch):
+    articles = [{"title": "RECENT", "publisher": "P", "link": "l",
+                 "providerPublishTime": _epoch("2026-09-10")},
+                {"title": "OLDER", "publisher": "P", "link": "l",
+                 "providerPublishTime": _epoch("2026-07-01")}]
+    _ticker_with(articles, monkeypatch)
+    out = ynews.get_news_yfinance("AAPL", "2026-08-07", "2026-08-14")
+    assert "No news found" in out
+    assert "unavailable" not in out
+
+
+@pytest.mark.unit
+@pytest.mark.parametrize("dates, expect_gap", [
+    ([], True),                                              # empty feed: covers at most now
+    ([None], True),                                          # undated only: same
+    ([datetime(2026, 5, 20, tzinfo=timezone.utc)], True),    # all after the window
+    ([datetime(2026, 5, 4, tzinfo=timezone.utc)], True),     # starts mid-window: partial
+    ([datetime(2026, 5, 1, 18, tzinfo=timezone.utc)], False),  # reaches the first day
+    ([datetime(2026, 5, 20, tzinfo=timezone.utc),
+      datetime(2026, 4, 1, tzinfo=timezone.utc)], False),    # coverage reaches back
+])
+def test_coverage_gap_boundaries(dates, expect_gap):
+    from tradingagents.dataflows.date_window import coverage_gap
+
+    out = coverage_gap(dates, "2026-05-01", "2026-05-08", "Feed", "items")
+    assert (out is not None) is expect_gap
+    if expect_gap:
+        assert "unavailable for 2026-05-01..2026-05-08" in out and "not an absence" in out
+
+
+
+@pytest.mark.unit
+def test_ticker_news_empty_feed_for_a_past_window_is_unavailable(monkeypatch):
+    _ticker_with([], monkeypatch)
+    out = ynews.get_news_yfinance("AAPL", "2026-08-07", "2026-08-14")
+    assert "unavailable" in out and "not an absence" in out
+
+
+@pytest.mark.unit
+def test_ticker_news_null_feed_is_handled(monkeypatch):
+    # Yahoo can return None instead of a list; that is unavailability, not an error.
+    _ticker_with(None, monkeypatch)
+    out = ynews.get_news_yfinance("AAPL", "2026-08-07", "2026-08-14")
+    assert "unavailable" in out and "Error" not in out
+
+
+@pytest.mark.unit
+def test_global_news_empty_feed_for_a_past_window_is_unavailable(monkeypatch):
+    class FakeSearch:
+        def __init__(self, *a, **k):
+            self.news = []
+
+    monkeypatch.setattr(ynews.yf, "Search", FakeSearch)
+    out = ynews.get_global_news_yfinance("2025-05-09", look_back_days=7, limit=10)
+    assert "unavailable" in out and "not an absence" in out
+
+
+@pytest.mark.unit
+def test_global_news_does_not_infer_coverage_from_a_stale_search_hit(monkeypatch):
+    # Global news merges fuzzy searches; one old hit before the window says
+    # nothing about the days in between, so the window stays unavailable.
+    stale = {"title": "STALE", "publisher": "P", "link": "l", "providerPublishTime": _epoch("2025-01-01")}
+    fresh = {"title": "FRESH", "publisher": "P", "link": "l", "providerPublishTime": _epoch("2025-06-01")}
+
+    class FakeSearch:
+        def __init__(self, *a, **k):
+            self.news = [fresh, stale]
+
+    monkeypatch.setattr(ynews.yf, "Search", FakeSearch)
+    out = ynews.get_global_news_yfinance("2025-05-09", look_back_days=7, limit=10)
+    assert "unavailable" in out and "No global news found" not in out
+
+
+@pytest.mark.unit
+def test_coverage_gap_future_window_is_unavailable():
+    from datetime import timedelta
+
+    from tradingagents.dataflows.date_window import coverage_gap
+    today = datetime.now(timezone.utc).date()
+    out = coverage_gap([], str(today), str(today + timedelta(days=3)), "Feed", "items")
+    assert out is not None and "past today" in out