SAFETY-78: maintenance drain at N=2 no longer stalls

At two inverters the drain pins its pack and the site target is split
around the pin. Below the pin the other pack had to charge, the allocator
refused the opposite directions, and the site sat at 0 W with an ARBITER
line every cycle (house below or above the drain rate, or a grid charge).

main.py now files a site limit `drain` (lo = what the pin places, at
P_MAINTENANCE) at N>=2 while a pack drains, so the other pack only adds
power in the same direction. A drain that cannot give power waits with
one log line. With battery modes on, no grid charge while a pack drains,
and the other battery's card says why. N=1 is byte-identical.

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

goodwe_controller/test_batteries_screen.py

@@ -93,7 +93,8 @@ WANT = {
     "off": ("solar_first", "off"),
     "off_peak": ("peak", "off_peak"),
     "refusal": ("refuses_give", "other_refuses"),
-    "maint": ("cycle_mode", "leftover"),
+    # SAFETY-78: the other battery says why it does not charge.
+    "maint": ("cycle_mode", "other_cycle"),
 }
 
 # ============================================================================ #
@@ -317,6 +318,14 @@ _cases = [
     (dict(role="charge", refused=-1), "refuses_charge"),
     (dict(role="sell", peak=True), "peak"),
     (dict(role="hold", off=True), "off"),
+    # SAFETY-78: another battery drains for its monthly cycle.
+    (dict(other_cycle="A"), "other_cycle"),
+    (dict(other_cycle="A", modes_on=False, giving=True), "other_cycle"),
+    (dict(other_cycle="A", mode=packmode.CHEAP_HOURS, role="charge"),
+     "other_cycle"),
+    (dict(other_cycle="A", peak=True), "peak"),
+    (dict(other_cycle="A", refused=-1), "refuses_charge"),
+    (dict(other_cycle="A", off=True), "off"),
 ]
 _wrong = [(kw, want, why(**kw)) for kw, want in _cases if why(**kw) != want]
 print(f"    {_wrong}")