fix(octopus): keep the current half hour out of the car-need gate

The surplus started at minutes_now, which usually falls mid-period, so the rest
of the current half hour lost its low rate once the car was full - even when
the car charged earlier in it, which makes Octopus bill the whole period cheap.
Surplus now starts at the next half-hour boundary. Clamping back to the start
of the current period instead would have marked elapsed minutes as surplus too,
and rate_add_io_slots() applies the skip to past minutes, misreporting today's
cost.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: chalfontchubby

apps/predbat/octopus.py

@@ -3819,6 +3819,9 @@ def octopus_surplus_minutes(self):
             return set()
         dispatch_minutes = set()
         needed_minutes = set()
+        # The current half hour is never surplus: the car may have charged earlier in it, which makes the whole
+        # period cheap, and once the car is full its slots no longer show that
+        next_period = ((self.minutes_now + 29) // 30) * 30
         for car_n in range(min(self.num_cars, len(self.octopus_slots), len(self.car_charging_slots))):
             car_slots = self.car_charging_slots[car_n]
             if not any(slot.get("octopus", False) for slot in car_slots):
@@ -3828,7 +3831,7 @@ def octopus_surplus_minutes(self):
                 if start_minutes == end_minutes:
                     continue
                 start_minutes, end_minutes = round_out_to_period(start_minutes, end_minutes)
-                dispatch_minutes.update(range(max(start_minutes, self.minutes_now), end_minutes))
+                dispatch_minutes.update(range(max(start_minutes, next_period), end_minutes))
             for slot in car_slots:
                 # A cancelled car's slots are zeroed with their kWh kept in kwh_cancelled (dynamic_load_car_check());
                 # cancellation decides their rate itself, so they still count as needed here

apps/predbat/tests/test_iog_car_need_gate.py

@@ -94,6 +94,15 @@ def run_surplus_minutes_tests(my_predbat):
     surplus = my_predbat.octopus_surplus_minutes()
     failed |= _expect("elapsed untouched", surplus == set(range(10 * 60, 11 * 60)), "expected 10:00-11:00 only")
 
+    # Mid half hour, with the car already full: the rest of the current half hour stays cheap (the car may have
+    # charged earlier in it), and nothing elapsed is ever touched
+    my_predbat.minutes_now = 14 * 60 + 10
+    my_predbat.octopus_slots = [[_slot(my_predbat, 13.5, 15, 20.0)]]
+    my_predbat.car_charging_slots = [[{"start": 14 * 60 + 10, "end": 15 * 60, "kwh": 0.0, "octopus": True}]]
+    surplus = my_predbat.octopus_surplus_minutes()
+    failed |= _expect("current half hour kept", surplus == set(range(14 * 60 + 30, 15 * 60)), "expected 14:30-15:00 only, got {}".format(sorted(surplus)[:1] + sorted(surplus)[-1:]))
+    my_predbat.minutes_now = 10 * 60
+
     # Rates are shared: a minute another car still needs stays cheap
     my_predbat.num_cars = 2
     my_predbat.octopus_slots = [[_slot(my_predbat, 13, 15, 20.0)], [_slot(my_predbat, 14, 14.5, 5.0)]]