OPT-27 round 3: the kept-forecast wording states the 12 h limit (text only)

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

goodwe_controller/test_opt27.py

@@ -7,8 +7,9 @@ Forecast.Solar site was "no forecast": a price mode's night cheap run needed
 fresh reading of each sensor, for the day it is FOR:
 
 * up to `FRESH_S` when the sensor is missing or unavailable (a short outage);
-* from the end of the bell (20:00) until local midnight + 3 h however old it
-  is (the night plan); never beyond, never for another day.
+* from the end of the bell (20:00) until local midnight + 3 h, if the reading
+  is at most `KEPT_MAX_AGE_S` (12 h) old when used (the night plan); never
+  beyond, never for another day.
 
 DECISIONS/OPT-27-last-fresh-forecast-for-the-night.md.
 
@@ -166,7 +167,7 @@ check("... its sun is counted on the day it is for (06:00-20:00 on the 4th)",
       and fmid.between(at(4, 3, 0), at(4, 7, 0)) > 0.0)
 check("03:01 (midnight + 3 h): not used any more",
       rs(GONE, GONE, at(4, 3, 1), h2)[0] is None)
-check("... and not the next evening either (older than one night)",
+check("... and not the next evening either (past midnight + 3 h)",
       rs(GONE, GONE, at(4, 22, 0), h2)[0] is None)
 fe = rs(st(0.1, at(4, 21, 50)), GONE, at(4, 22, 0), h2)[0]
 check("... the next evening, with today fresh and tomorrow's sensor down, "