OPT-20: a refusal probe asks only PROBE_W, not the whole trade

The probe's trade was sized at the probing battery's rating. Its SAFETY-73
pin held 200 W of that, and the allocator put the rest on a battery with no
mode range (one in a maintenance phase): TEST-23 OPT-15 g7, -2300 W on A in
its maintenance charge for 34 s, grid 3100 W.

modetrade.decide() now asks PROBE_W for the probing battery plus what the
other chargers would have had without the probe; size() adds the probe on top
of their share, or files PROBE_W exactly, or nothing. _mode_trade() carries
the pin only on the ticks it is filed, so the window's first and last cycle
do not move another battery's share either. Modes off and modes on with no
probe are unchanged (bf9019e digests). Tests: test_opt20.py.

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

goodwe_controller/DECISIONS/OPT-11-battery-modes.md

@@ -132,6 +132,23 @@ P1 is its section 6 P1, and the pull request lists what was measured.
     own, and a rise past that is the peak floor's, which ends the hold.
     A maintenance drain, hold or charge that starts during the hold ends it
     on that tick (replayed at edge + 3 s).
+- OPT-20 (TEST-23 OPT-15 g7, `test_opt20.py`): a probe asks only PROBE_W.
+  The trade was sized at the probing battery's rating (2500 W), B's pin held
+  200 W of it, and the allocator put the other 2300 W on A, in its
+  maintenance charge phase (no mode range there, so nothing kept it out):
+  grid 3100 W for 34 s. Now the ask is PROBE_W for the probing battery plus
+  what the other chargers would have had without the probe (none: 200 W
+  alone), and it carries the pin only on the ticks the pin is filed (the
+  window's first and last cycle moved another battery's share by 200 W).
+  - Chosen: the probe sits on top of a headroom-sized charge, so beside a
+    normal charger its command is the same and the grid rises 200 W (about
+    7 W on the quarter) rather than that charger giving 200 W up. A probe
+    that the headroom or the bound cannot hold at 200 W is not filed.
+  - Unchanged, same on bf9019e: with a charge ask the other batteries cannot
+    give (one sign), so an idle-looking A that gives the house stops for the
+    window and the grid rises by what it gave. The trade line now says 200 W
+    for a probe alone; its words are UX-38's. The base P4 F4 path (a normal
+    trade on a battery in maintenance charge) is not touched.
 
 ## P4: the solar forecast and the day plan (2026-09-29)
 - Input: a Home Assistant forecast sensor (`pv_forecast_entity`, kWh left