Fix market data bugs found in code review

backend/app/market/massive_client.py

@@ -102,12 +102,15 @@ async def _poll_once(self) -> None:
                     # Massive timestamps are Unix milliseconds → convert to seconds
                     timestamp = snap.last_trade.timestamp / 1000.0
 
-                    # Best-effort previous-close anchor. If the field is missing/None on
-                    # this snapshot (pre-market, a thin plan tier, a transient partial
-                    # response), fall back silently to PriceCache's own "first observed"
-                    # default by passing anchor=None — never let a missing anchor drop
-                    # the price update.
+                    # Best-effort previous-close anchor. If the field is missing/None/zero
+                    # on this snapshot (pre-market, a thin plan tier, a transient partial
+                    # response, a newly-listed ticker with no prior close), fall back
+                    # silently to PriceCache's own "first observed" default by passing
+                    # anchor=None — never let a missing anchor drop the price update, and
+                    # never anchor day-change math on a zero baseline.
                     anchor = getattr(getattr(snap, "day", None), "previous_close", None)
+                    if not anchor:
+                        anchor = None
 
                     self._cache.update(
                         ticker=snap.ticker,

backend/app/market/reconcile.py

@@ -56,7 +56,7 @@ async def on_watchlist_remove(source: MarketDataSource, db: TrackedTickerStore,
     position for this ticker — an open position keeps it priced even off the
     watchlist."""
     position = await db.get_position(ticker)
-    if position is None or position.quantity == 0:
+    if position is None or position.quantity <= 0:
         await source.remove_ticker(ticker)
 
 
@@ -70,9 +70,8 @@ async def on_trade_executed(source: MarketDataSource, db: TrackedTickerStore, ti
        that nothing references it, stop tracking it.
     """
     position = await db.get_position(ticker)
-    on_watchlist = await db.is_on_watchlist(ticker)
 
     if position and position.quantity > 0:
         await source.add_ticker(ticker)  # covers case 1; no-op if already tracked
-    elif not on_watchlist:
+    elif not await db.is_on_watchlist(ticker):
         await source.remove_ticker(ticker)  # covers case 2

backend/app/market/validation.py

@@ -23,7 +23,10 @@ def validate_ticker(raw: str) -> str:
         - LLM `trades[].ticker`             (chat-initiated trade)
         - LLM `watchlist_changes[].ticker`  (chat-initiated watchlist change)
     """
-    ticker = raw.strip().upper()
-    if not _TICKER_RE.match(ticker):
+    stripped = raw.strip()
+    ticker = stripped.upper()
+    # Some Unicode codepoints expand under .upper() (e.g. 'ß' -> 'SS'), which could
+    # otherwise slip a non-ASCII, non-letter input through the length/format check below.
+    if not stripped.isascii() or not _TICKER_RE.match(ticker):
         raise InvalidTickerError(f"Invalid ticker '{raw}': must be 1-5 letters (A-Z).")
     return ticker

backend/tests/market/test_massive.py

@@ -232,6 +232,21 @@ async def test_missing_previous_close_falls_back_to_first_observed(self):
 
         assert cache.get_anchor("AAPL") == 190.50
 
+    async def test_zero_previous_close_falls_back_to_first_observed(self):
+        """A previous_close of 0.0 (thin snapshot / newly-listed ticker) must not be
+        treated as a real anchor, or day-change% would be pinned to a bogus baseline."""
+        cache = PriceCache()
+        source = MassiveDataSource(api_key="test-key", price_cache=cache, poll_interval=60.0)
+        source._tickers = ["AAPL"]
+        source._client = MagicMock()
+
+        snap = _make_snapshot("AAPL", 190.50, 1707580800000, previous_close=0.0)
+
+        with patch.object(source, "_fetch_snapshots", return_value=[snap]):
+            await source._poll_once()
+
+        assert cache.get_anchor("AAPL") == 190.50
+
     async def test_anchor_stays_sticky_across_polls(self):
         """Test that a later poll's previous_close does not overwrite the captured anchor."""
         cache = PriceCache()

backend/tests/market/test_reconcile.py

@@ -120,6 +120,15 @@ async def test_remove_watchlist_unknown_ticker_removes(self):
         await on_watchlist_remove(source, db, "NOPE")
         assert source.remove_called
 
+    async def test_remove_watchlist_tiny_negative_quantity_removes(self):
+        """Guards against float drift (e.g. -1e-16) after a 'full' sell leaving
+        quantity just below zero instead of exactly 0.0."""
+        db = FakeDB()
+        db.set_position("AAPL", quantity=-1e-16)
+        source = FakeSource()
+        await on_watchlist_remove(source, db, "AAPL")
+        assert source.remove_called
+
 
 @pytest.mark.asyncio
 class TestOnTradeExecuted:

backend/tests/market/test_validation.py

@@ -30,6 +30,12 @@ def test_invalid_tickers_raise(self, raw):
         with pytest.raises(InvalidTickerError):
             validate_ticker(raw)
 
+    def test_unicode_case_folding_expansion_rejected(self):
+        """'ß'.upper() == 'SS' would otherwise pass the 1-5-letter regex despite
+        being a single non-ASCII character, not 1-5 letters in the input."""
+        with pytest.raises(InvalidTickerError):
+            validate_ticker("ß")
+
     def test_error_message_includes_original_input(self):
         with pytest.raises(InvalidTickerError, match="NOT-A-TICKER"):
             validate_ticker("NOT-A-TICKER")