OPT-15: price-run fixes (quarter edge, charge-end overshoot, refusal probe)

F1: with battery modes on, the peak guard projects the quarter `now` is in
even before its first P1 sample (PeakTracker.project(roll=True)), and only
a measured stop latches the period. The edge tick no longer reads "no
seconds left", so a charge is not stopped and latched at a quarter edge.

F2: after a run edge the loop is held at E until the meter shows the step
(EDGE_HOLD_S, longer while the battery still moves). The replay gained a
lag model (dead time, reading age, P1 debounce, 1 s cycles) that shows
TEST-23's overshoot without the hold.

F3: a charge refuser's SAFETY-73 probe inside a cheap run is a charger
pinned at PROBE_W, the others rest, so the probe actually runs.

Modes off stays byte-identical to 5a4cdc2 (new late-P1 identity scenarios).

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

goodwe_controller/DOCS.md

@@ -537,9 +537,9 @@ With battery modes on, these choices replace the *Charging and selling on price*
 
 **What always comes first.**
 - The peak limit, the safety stops and the monthly cycle come before a battery's mode.
-- A grid charge is sized so the 15-minute period stays under the peak limit less its margin (`peak_margin_w`). It starts only at 500 W or more. Once the peak limit stops it, it stays off for the rest of that 15-minute period.
+- A grid charge is sized so the 15-minute period stays under the peak limit less its margin (`peak_margin_w`). It starts only at 500 W or more. Once the peak limit stops it, it stays off for the rest of that 15-minute period. The start of a new period does not stop it.
 - While one battery charges from the grid, the others rest, and the house uses the grid.
-- A battery that refuses to charge or give power takes no part in a run in that direction.
+- A battery that refuses to charge or give power takes no part in a run in that direction. In a cheap run it is still tested every 15 minutes: it charges at 200 W for about half a minute while the others rest.
 
 **In Home Assistant.** With MQTT set up, each battery also gets a *Mode* list and a *Use* switch, for example `select.goodwe_inverter_a_mode` and `switch.goodwe_inverter_a_use`. They do the same as the Batteries screen. Turn battery modes off and restart, and they are removed.
 
@@ -547,7 +547,7 @@ With battery modes on, these choices replace the *Charging and selling on price*
 
 *For installers:* a mode is a limit at priority 35, kept apart from the hard limits. It gives way only as far as a limit above it (the peak guard) needs. A mode range always holds 0 W, so a mode can forbid a direction and never force one. With one inverter the mode also bounds the loop. The record is `DECISIONS/OPT-11-battery-modes.md`.
 
-*For installers:* when a charge or sale ends, the loop restarts at the house's own level rather than at the trade's watts. On the replay model that removes a ~3 kW import spike after a 2.5 kW charge and halves the settling time; about 0.1 × the battery's power still overshoots as export. The *Mode* list gains *Cheap hours only* in Home Assistant, at the end.
+*For installers:* when a charge or sale ends, the loop restarts at the house's own level rather than at the trade's watts, and holds there until the meter shows the change (at most 18 s, up to 36 s while the battery is still moving). This removes the ~3 kW import spike after a 2.5 kW charge and the export overshoot that readings a second or two old caused (-1120 W on the test rig); with the hold it stays within 0.15 × the battery's power. The *Mode* list gains *Cheap hours only* in Home Assistant, at the end.
 
 ### Reading the grid-following loop: `Loop integrator`, `Loop integrator lead`, `Loop reason`