fix: don't slow EMA smoother across zero-crossings for high alpha (#373)

The sign-flip "catchup" branch in SmoothedPowermeter was meant to react
faster when raw power crosses zero by boosting the effective alpha to
`alpha * 4`, capped at 0.5. But `min(0.5, alpha * 4)` is only a boost
while `alpha < 0.125`; for any larger configured alpha it just clamps to
0.5, and for alpha > 0.5 it actively reduces the step.

Users running near self-consumption with a high `SMOOTH_TARGET_ALPHA`
(e.g. 1.0 for instant tracking) therefore saw randomly halved deltas
whenever the raw reading happened to straddle zero, often dragging the
smoothed value back into the deadband and snapping it to 0.

Raise the catchup alpha to at least the configured alpha so the branch
can only ever speed the smoother up, never slow it down.

Refs #371

Co-authored-by: Claude <noreply@anthropic.com>

Author: tomquist

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Next
 
+- **Fixed** EMA smoother slowing down across zero-crossings when `SMOOTH_TARGET_ALPHA` was configured above 0.5: the sign-flip "catchup" branch capped the effective alpha at 0.5, which actually reduced responsiveness for users who picked a larger alpha (e.g. 1.0 for near-instant tracking). The catchup boost now never drops below the configured alpha ([#371](https://github.com/tomquist/astrameter/issues/371)).
 
 ## 2.0.1
 

src/astrameter/powermeter/wrappers/smoothing.py

@@ -74,7 +74,7 @@ async def get_powermeter_watts(self) -> list[float]:
 
         catchup_alpha = self._alpha
         if (raw_total > 0) != (self._value > 0):
-            catchup_alpha = min(0.5, self._alpha * 4)
+            catchup_alpha = max(self._alpha, min(0.5, self._alpha * 4))
         delta = catchup_alpha * (raw_total - self._value)
 
         if self._max_step > 0:

src/astrameter/powermeter/wrappers/smoothing_test.py

@@ -82,10 +82,27 @@ async def test_sign_change_catchup(self):
         # Sign flip: raw goes negative
         fake.set([-100.0])
         await sm.get_powermeter_watts()
-        # catchup_alpha = min(0.5, 0.1 * 4) = 0.4
+        # catchup_alpha = max(0.1, min(0.5, 0.1 * 4)) = 0.4
         # delta = 0.4 * (-100 - 100) = -80 → new = 20
         assert sm.smoothed_value == pytest.approx(20.0)
 
+    @pytest.mark.asyncio
+    async def test_sign_change_does_not_slow_high_alpha(self):
+        fake = FakePowermeter([1.0])
+        sm = SmoothedPowermeter(fake, alpha=1.0)
+
+        await sm.get_powermeter_watts()
+        assert sm.smoothed_value == 1.0
+
+        # Sign flip: the catchup branch must not reduce alpha below the
+        # configured value, otherwise large user-chosen alphas (e.g. 1.0)
+        # respond slower across zero-crossings than they do anywhere else.
+        fake.set([-99.0])
+        await sm.get_powermeter_watts()
+        # catchup_alpha = max(1.0, min(0.5, 4.0)) = 1.0
+        # delta = 1.0 * (-99 - 1) = -100 → new = -99
+        assert sm.smoothed_value == pytest.approx(-99.0)
+
     @pytest.mark.asyncio
     async def test_max_step_limits_delta(self):
         fake = FakePowermeter([100.0])