OPT-27: the night plan keeps the last fresh solar forecast

Forecast.Solar's sensors stop updating in the evening, so at night every such
site had no forecast: the night cheap run needed 1.5x the cycle cost and
Leftover solar planned nothing. One missed poll also dropped it at once.

solarfc.Hold keeps the last fresh reading of each sensor, for the day it is
for. A missing or stale sensor is covered by it for up to FRESH_S (a short
outage), and from the end of the bell (20:00) until local midnight + 3 h
however old. A tomorrow figure is tomorrow's until midnight and then today's;
a today figure is only today's. Stored in the controller's store
(solar_fc_hold), so an evening restart keeps it. The forecast line says
'Solar forecast read 17:05, used for tonight's plan.' (EN, NL).

test_tariff24_weather.py runs with a hold that never covers: it tests what the
plan does when the forecast IS lost.

Co-Authored-By: Claude <noreply@anthropic.com>

goodwe_controller/app/main.py

@@ -208,6 +208,9 @@ EDGE_HOLD_S = _ctl.PLANT_SETTLE_S
 # OPT-11 P4: the store key of the house profile (dayplan.HouseProfile), and
 # how often the forecast sensors are read (they change hourly at most).
 HOUSE_PROFILE_KEY = "house_profile"
+# OPT-27: the forecast sensors' last fresh readings (`solarfc.Hold`), so an
+# evening restart keeps the figure the night plan uses.
+FC_HOLD_KEY = "solar_fc_hold"
 FORECAST_READ_S = 60.0
 
 
@@ -995,6 +998,8 @@ class Controller:
         self.solar_fc_why = (solarfc.NOT_SET if self.fc_entity is None
                              else solarfc.MISSING)
         self._fc_read_mono = None
+        self.fc_hold = solarfc.Hold(
+            (getattr(store, "data", None) or {}).get(FC_HOLD_KEY))
         self.day_plan = None
         self._plan_targets = None
         self.house_profile = None
@@ -3406,17 +3411,25 @@ class Controller:
         now = datetime.now(timezone.utc)
         fc, why, gaps = solarfc.read_sum(
             list(zip(self.fc_entities, states[:n])),
-            list(zip(self.fc_tomorrow_entities, states[n:])), now)
+            list(zip(self.fc_tomorrow_entities, states[n:])), now,
+            hold=self.fc_hold)
+        if self.fc_hold.changed:
+            self.fc_hold.changed = False
+            self.store.set(FC_HOLD_KEY, self.fc_hold.dump())
         # A member is named only in a sum of several; one entity reads as
         # before. Logged once per episode: on a change, never every read.
         gaps = tuple(g for g in gaps if len(
             self.fc_entities if g[0] == "today"
             else self.fc_tomorrow_entities) > 1)
+        was_kept = bool(self.solar_fc is not None and self.solar_fc.kept)
         if (fc is None) != (self.solar_fc is None) \
-                or why != self.solar_fc_why or gaps != self.solar_fc_gaps:
+                or why != self.solar_fc_why or gaps != self.solar_fc_gaps \
+                or bool(fc is not None and fc.kept) != was_kept:
             self.log_event(
-                "solar forecast: " + ("read" if fc is not None else
-                                      f"none ({why})")
+                "solar forecast: " + (
+                    "none (" + str(why) + ")" if fc is None else
+                    f"read, kept from {brussels(fc.at):%H:%M}" if fc.kept
+                    else "read")
                 + "".join(f", {d} {e} not usable ({w})"
                           for d, _i, e, w in gaps),
                 hint=messages.hint(