Fix Massive API timestamp unit conversion (ns, not ms)

backend/app/market/massive_client.py

@@ -99,8 +99,8 @@ async def _poll_once(self) -> None:
             for snap in snapshots:
                 try:
                     price = snap.last_trade.price
-                    # Massive timestamps are Unix milliseconds → convert to seconds
-                    timestamp = snap.last_trade.timestamp / 1000.0
+                    # Massive client timestamps are Unix nanoseconds → convert to seconds
+                    timestamp = snap.last_trade.timestamp / 1_000_000_000
                     self._cache.update(
                         ticker=snap.ticker,
                         price=price,

backend/tests/market/test_massive.py

@@ -8,13 +8,13 @@
 from app.market.massive_client import MassiveDataSource
 
 
-def _make_snapshot(ticker: str, price: float, timestamp_ms: int) -> MagicMock:
+def _make_snapshot(ticker: str, price: float, timestamp_ns: int) -> MagicMock:
     """Create a mock Massive snapshot object."""
     snap = MagicMock()
     snap.ticker = ticker
     snap.last_trade = MagicMock()
     snap.last_trade.price = price
-    snap.last_trade.timestamp = timestamp_ms
+    snap.last_trade.timestamp = timestamp_ns
     return snap
 
 
@@ -34,8 +34,8 @@ async def test_poll_updates_cache(self):
         source._client = MagicMock()  # Satisfy the _poll_once guard
 
         mock_snapshots = [
-            _make_snapshot("AAPL", 190.50, 1707580800000),
-            _make_snapshot("GOOGL", 175.25, 1707580800000),
+            _make_snapshot("AAPL", 190.50, 1707580800000000000),
+            _make_snapshot("GOOGL", 175.25, 1707580800000000000),
         ]
 
         with patch.object(source, "_fetch_snapshots", return_value=mock_snapshots):
@@ -55,7 +55,7 @@ async def test_malformed_snapshot_skipped(self):
         source._tickers = ["AAPL", "BAD"]
         source._client = MagicMock()  # Satisfy the _poll_once guard
 
-        good_snap = _make_snapshot("AAPL", 190.50, 1707580800000)
+        good_snap = _make_snapshot("AAPL", 190.50, 1707580800000000000)
         bad_snap = MagicMock()
         bad_snap.ticker = "BAD"
         bad_snap.last_trade = None  # Will cause AttributeError
@@ -84,7 +84,7 @@ async def test_api_error_does_not_crash(self):
         assert cache.get_price("AAPL") is None  # No update happened
 
     async def test_timestamp_conversion(self):
-        """Test that timestamps are converted from milliseconds to seconds."""
+        """Test that timestamps are converted from nanoseconds to seconds."""
         cache = PriceCache()
         source = MassiveDataSource(
             api_key="test-key",
@@ -94,7 +94,7 @@ async def test_timestamp_conversion(self):
         source._tickers = ["AAPL"]
         source._client = MagicMock()  # Satisfy the _poll_once guard
 
-        mock_snapshots = [_make_snapshot("AAPL", 190.50, 1707580800000)]
+        mock_snapshots = [_make_snapshot("AAPL", 190.50, 1707580800000000000)]
 
         with patch.object(source, "_fetch_snapshots", return_value=mock_snapshots):
             await source._poll_once()
@@ -189,7 +189,7 @@ async def test_start_immediate_poll(self):
         cache = PriceCache()
         source = MassiveDataSource(api_key="test-key", price_cache=cache, poll_interval=60.0)
 
-        mock_snapshots = [_make_snapshot("AAPL", 190.50, 1707580800000)]
+        mock_snapshots = [_make_snapshot("AAPL", 190.50, 1707580800000000000)]
 
         with patch("app.market.massive_client.RESTClient"):
             with patch.object(source, "_fetch_snapshots", return_value=mock_snapshots):

planning/MARKET_DATA_DESIGN.md

@@ -192,8 +192,9 @@ Design decisions:
 - **`change` / `change_percent` / `direction` are computed properties, not stored fields.**
   They are pure functions of `price` and `previous_price`, so storing them would be a
   chance to store them inconsistently. `to_dict()` materialises them for the wire.
-- **`timestamp` is Unix seconds (float).** Massive returns milliseconds; the client divides
-  by 1000 at the boundary so everything inside the layer speaks one unit.
+- **`timestamp` is Unix seconds (float).** Massive's `last_trade.timestamp` is in
+  nanoseconds; the client divides by `1_000_000_000` at the boundary so everything inside
+  the layer speaks one unit.
 
 Worked example:
 
@@ -1101,8 +1102,8 @@ class MassiveDataSource(MarketDataSource):
             for snap in snapshots:
                 try:
                     price = snap.last_trade.price
-                    # Massive timestamps are Unix milliseconds → convert to seconds
-                    timestamp = snap.last_trade.timestamp / 1000.0
+                    # Massive client timestamps are Unix nanoseconds → convert to seconds
+                    timestamp = snap.last_trade.timestamp / 1_000_000_000
                     self._cache.update(
                         ticker=snap.ticker,
                         price=price,
@@ -1711,7 +1712,7 @@ if price is not None:
 self._cache.update(
     ticker=snap.ticker,
     price=snap.last_trade.price,
-    timestamp=snap.last_trade.timestamp / 1000.0,
+    timestamp=snap.last_trade.timestamp / 1_000_000_000,
     baseline=getattr(snap.day, "previous_close", None) or None,
 )
 ```