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_modes.py

@@ -112,6 +112,11 @@ try:
 finally:
     _undo_c()
     _undo_b()
+# SAFETY-78 changes n2_maint ON PURPOSE: on a5dddad and 5a4cdc2 its N=2 drain
+# was refused on 392 of 540 cycles (site at 0 W); now none is. Printed on the
+# SAFETY-78 tree the same way. Every other digest is unchanged.
+SAFETY78_N2_MAINT = \
+    "cd4d9cb5b7e29ff4ab4fe65dab5106683d8a599f09323fbdee4018ad9b28fcd1"
 for k in A5DDDAD:
     print(f"    {k:7} {'same' if _now[k] == A5DDDAD[k] else 'DIFFERS'} "
           f"{_now[k][:16]}")
@@ -119,8 +124,13 @@ check("⭐ at N=1 and N=2, with the option absent and with it false, every "
       "command, reason and allocation record over 540 cycles each is "
       "byte-identical to a5dddad (house steps, a solar surplus, a battery "
       "at its cut-out level, at N=2 a refusal with probes, both batteries "
-      "due for maintenance), and so is the arbiter on 6000 claim lists",
-      _now == A5DDDAD)
+      "due for maintenance; n2_maint apart, below), and so is the arbiter "
+      "on 6000 claim lists",
+      {k: v for k, v in _now.items() if k != "n2_maint"}
+      == {k: v for k, v in A5DDDAD.items() if k != "n2_maint"})
+check("...and n2_maint is the SAFETY-78 digest: the N=2 drain that a5dddad "
+      "refused on 392 of 540 cycles now runs (test_safety78.py)",
+      _now["n2_maint"] == SAFETY78_N2_MAINT != A5DDDAD["n2_maint"])
 check("...and no cycle in those runs filed a `mode` claim or handed "
       "`compute()` a bound",
       _claims and not any(c.source == "mode" for cl in _claims for c in cl)