Prevent rejected CPR positions from validating repeats (#204)

* fix(pipe): keep rejected CPR positions out of trusted history

* Format CPR position history update

---------

Co-authored-by: Paul de Jong <paul.de.jong@knmi.nl>

Author: paulmadejong

src/pyModeS/_pipe.py

@@ -674,12 +674,10 @@ def _update_position_history(
         lon: float,
         timestamp: float,
     ) -> None:
-        """Insert into the per-ICAO time-ordered ring buffer.
+        """Insert a trusted position into the per-ICAO time-ordered ring buffer.
 
-        Called for every resolved CPR pair regardless of whether
-        `_motion_consistent` accepted it — rejected positions still
-        enter the buffer so future real positions can find corroborating
-        neighbours even after a streak of phantoms.
+        Callers add positions only after motion consistency or bootstrap
+        validation. Rejected candidates must not validate themselves or repeats.
         """
         history = self._position_history.setdefault(icao, [])
         history.append((lat, lon, timestamp))
@@ -959,7 +957,10 @@ def _handle_cpr_pair(
                             d["latitude"] = None
                             d["longitude"] = None
                         self._stats["position_rejected"] += 1
-                    self._update_position_history(icao, lat, lon, position_timestamp)
+                    if accepted:
+                        self._update_position_history(
+                            icao, lat, lon, position_timestamp
+                        )
                     if (
                         accepted
                         and bds == "0,5"

tests/test_pipe.py

@@ -1284,8 +1284,16 @@ def test_rejection_increments_stat_and_clears_fields(self):
         # Pair was resolved but rejected — lat/lon must be absent or None
         assert r.get("latitude") in (None, 0, False) or r["latitude"] is None
         assert pipe.stats["position_rejected"] == 1
-        # Ring buffer still updated with the rejected position
-        assert len(pipe._position_history[self.ICAO]) == 3
+        assert len(pipe._position_history[self.ICAO]) == 2
+
+        # Repeating the same CPR pair must not be accepted because the first
+        # rejected position was not added to trusted history.
+        pipe.decode("8D40058B58C901375147EFD09357", timestamp=1002.0)
+        repeated = pipe.decode("8D40058B58C904A87F402D3B8C59", timestamp=1003.0)
+        assert repeated.get("latitude") is None
+        assert repeated.get("longitude") is None
+        assert pipe.stats["position_rejected"] == 2
+        assert len(pipe._position_history[self.ICAO]) == 2
 
     def test_eviction_prunes_old_position_history(self):
         pipe = PipeDecoder(eviction_ttl=10.0)