TARIFF-24 round 2: a usable solar forecast replaces the "no weather" x1.5 (AUDIT-02 F1)

With battery modes on, the price gap a mode needs was always widened x1.5 by
Uncertainty.NO_WEATHER, even with a solar forecast read, so a 0.08 day/night
gap never traded at the shipped cycle cost. The doubt is now added only when
no usable forecast is read (solar_fc is None, the day plan's own test), in the
run plan (_price_runs), the charge gate (_mode_roles) and Home's mirror
(homeview.trade_verdict). The rule is one helper, arbitrage.weather_uncertainty();
the modes-off trade path (main.py cycle) keeps its literal NO_WEATHER.

DOCS "Battery modes" sentence, CHANGELOG 0.19.1 line and the DECISIONS note
follow. Tests: test_tariff24_weather.py.

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

goodwe_controller/DECISIONS/TARIFF-24-modes-need-the-tariff-task.md

@@ -33,3 +33,32 @@ exactly what the cycle sees without the task.
 battery on Solar first. The same cause, and this fix clears it for a site with
 a static profile (`test_tariff24.py` part 5). A site with no profile and no
 feed still has no prices, and Home still says so.
+
+## Round 2 (AUDIT-02 F1): the forecast replaces the "no weather" doubt
+
+**Decided 2026-10-28 (owner), in the same hotfix.** The price gap a mode needs
+was `cycle_cost_threshold_eur` x 1.5 (`Uncertainty.NO_WEATHER`) whether or not
+a solar forecast was read. At the shipped cost 0.10 that is 0.15, so a
+day/night gap (0.08) and many dynamic days never traded, and the screens said
+only "Prices differ too little".
+
+**Why the doubt goes with a forecast.** The widening stands in for not knowing
+the weather. The forecast is that knowledge, and the day plan already trusts it
+for how much to charge. Trusting it for the plan but doubting it for the gap
+was one input judged twice.
+
+**The rule** (`arbitrage.weather_uncertainty()`). With battery modes on and a
+usable forecast (`solar_fc` not None, the day plan's own test) the doubt is
+not added: the gap needed is the cycle cost, widened by the price product only.
+No forecast, or a stale or unusable one: 1.5 x, as before. It is read in three
+places that must agree: the run plan (`_price_runs()`), the charge gate
+(`_mode_roles()`) and Home's mirror (`homeview.trade_verdict()`). The forecast
+is read at most every 60 s and the plan key already holds "forecast or not", so
+the gap follows in the cycle the read changes, both ways. A run already under
+way is kept to its end (`priceruns.keep_started()`), as for any change.
+
+**Not changed.** Modes off (the site trade) keeps the doubt always. The
+shipped cost 0.10 still needs a gap of 0.10 even with a forecast: a 0.08
+day/night site must set *Battery cycle cost* to 0.08 or less. Showing the two
+numbers on the screens (AUDIT-02 F1 option b) is a separate card.
+