Optimize signal read paths and enforce score invariants

tests/unit/test_alert_service.py

@@ -95,7 +95,17 @@ async def test_score_drop_seeds_then_alerts(session):
     msgs = await svc._collect_score_drops(session)
     await session.commit()
     assert msgs == []
-    assert await svc._watermark(session, "AAA") == 80.0
+    watermarks = (
+        await session.execute(
+            select(AlertLog.value)
+            .where(
+                AlertLog.alert_type == svc.WATERMARK_TYPE,
+                AlertLog.dedup_key == "AAA",
+            )
+            .order_by(AlertLog.created_at.desc(), AlertLog.id.desc())
+        )
+    ).scalars().all()
+    assert watermarks == [80.0]
 
     # Drop the composite well past the threshold
     row = (await session.execute(
@@ -111,7 +121,71 @@ async def test_score_drop_seeds_then_alerts(session):
     assert key == "scoredrop:AAA"
     assert "AAA" in text
     # rebaselined to the new (lower) level
-    assert await svc._watermark(session, "AAA") == 60.0
+    watermarks = (
+        await session.execute(
+            select(AlertLog.value)
+            .where(
+                AlertLog.alert_type == svc.WATERMARK_TYPE,
+                AlertLog.dedup_key == "AAA",
+            )
+            .order_by(AlertLog.created_at.desc(), AlertLog.id.desc())
+        )
+    ).scalars().all()
+    assert watermarks[0] == 60.0
+
+
+async def test_score_drop_uses_latest_watermark_when_timestamps_tie(session):
+    await _seed_watchlisted_ticker(session, "AAA", 50.0)
+    timestamp = datetime.now(timezone.utc)
+    session.add_all([
+        AlertLog(
+            alert_type=svc.WATERMARK_TYPE,
+            dedup_key="AAA",
+            value=90.0,
+            created_at=timestamp,
+        ),
+        AlertLog(
+            alert_type=svc.WATERMARK_TYPE,
+            dedup_key="AAA",
+            value=70.0,
+            created_at=timestamp,
+        ),
+    ])
+    await session.commit()
+
+    msgs = await svc._collect_score_drops(session)
+
+    assert len(msgs) == 1
+    assert "from 70" in msgs[0][1]
+
+
+async def test_score_drop_seeds_when_latest_watermark_has_no_value(session):
+    await _seed_watchlisted_ticker(session, "AAA", 80.0)
+    session.add(
+        AlertLog(
+            alert_type=svc.WATERMARK_TYPE,
+            dedup_key="AAA",
+            value=None,
+            created_at=datetime.now(timezone.utc),
+        )
+    )
+    await session.commit()
+
+    msgs = await svc._collect_score_drops(session)
+    await session.commit()
+
+    assert msgs == []
+    values = (
+        await session.execute(
+            select(AlertLog.value)
+            .where(
+                AlertLog.alert_type == svc.WATERMARK_TYPE,
+                AlertLog.dedup_key == "AAA",
+            )
+            .order_by(AlertLog.created_at.desc(), AlertLog.id.desc())
+        )
+    ).scalars().all()
+    assert values[0] == 80.0
 
 
 def test_format_qualified_includes_current_price_and_target_move():