OPT-23, OPT-28: the day plan counts the sun right, and the night charge covers the expensive-hour shortfall

OPT-23: a state-only forecast is read from now for every span
(Forecast.between since=), so the plan's per-hour sun adds up to the day's
figure, today and tomorrow. Hourly splits are unchanged. The Forecast tab
reads spans the same way.

OPT-28: a Leftover solar battery buys, from the floor, the sum over the
expensive hours of max(0, house - trust x sun), / EFF. Several Leftover
solar batteries hold it together by capacity, the ceiling passes the rest
on, and what none can hold is said (Plan.uncovered_kwh). Home's grid block,
the Batteries line and the mode help (EN + NL) say the level, what it
covers, and that Leftover solar buys only what the sun will not give.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/DECISIONS/OPT-23-28-the-night-charge-covers-the-dear-hours.md

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+# OPT-23 and OPT-28 - the day plan counts the sun right, and the night charge covers the expensive-hour shortfall
+
+**Status: for review.** Tests: `test_opt23_28.py`.
+
+`dayplan.plan()` now buys, for Leftover solar batteries, what the house uses in the expensive hours less the sun counted for each hour, shared by capacity, and reads a state-only forecast from now for every span (OPT-23).
+
+- **Shortfall.** `sum_h max(0, house_h - trust x sun_h)` over every expensive hour, `/ EFF`, from the floor. It replaces the use over the run with no sun counted, which on a day and night tariff bought for the whole day (G1, `reports/UX-69-design-report.md`). The sun before the run is unchanged. A run with its dear hours after sunset gives the old number.
+- **House use.** An hour with sun is read at no less than the night base, as the sun sum reads it (the profile is net of the sun). An hour without is read as measured. An hour with no forecast counts no sun.
+- **Several batteries.** One total, shared by capacity with the ceiling passed on (`dayplan._spread()`). With the same floor and ceiling for all, they reach the ceiling together, so a shortfall that one battery cannot hold fills both to the same level, not one first. More than all hold: all go to the ceiling, `Plan.uncovered_kwh` is the rest, and the grid carries it at the expensive price.
+- **Cheap hours** still fills up and is not counted in the share; **Solar first** still never charges from the grid. The mode help says so.
+- **Not done:** the run length (OPT-25); netting what a Cheap hours or Solar first battery will hold against the shortfall.