Merge release/1.0 (SAFETY-78, #154) into opt11-p4-solar-forecast

Conflicts: modetrade.decide() takes both the day plan (targets) and
SAFETY-78's draining flag; the Why line keeps SAFETY-78's other_cycle
ahead of the plan's word (test added).

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

goodwe_controller/DECISIONS/MAINT-05-per-pack-maintenance.md

@@ -285,32 +285,11 @@ cross-inverter `lo > hi` contradiction at `arbiter.py:114`. The only line this
 card changed there is **which** roster entry the claim is filed on: the one whose
 state machine produced the result, rather than `inverters[0]`.
 
-## 6. FOUND AND NOT FIXED: the site loop still contradicts a drain at N>=2
+## 6. FIXED BY SAFETY-78: the site loop contradicted a drain at N>=2
 
-Measured while wiring this card, and **pre-existing on `release/1.0` at
-`2d025ee`** — the same drain filed on `inverters[0]` produces the identical
-refusal with the two unit names swapped.
-
-The maintenance SET **pins** its pack. The loop's target is a **site** claim.
-When the site target is *below* the pin — a 2000 W drain while the house imports
-less than that, which is most of a night — the only split that sums to the site
-target asks the sibling to **charge** while the maintained pack **discharges**,
-and `allocator.plan()` refuses it by name as circulating power. The refusal is
-correct and fails safe: the whole site goes to 0 W with an `ARBITER: REFUSED`
-line in the action log.
-
-**The consequence an operator would see is a misdiagnosis.** The pack is held at
-0 W while its state machine believes it is draining, so after 12 h the DRAIN
-timeout fires and reports *"drain stuck"* — §12's words for a battery that is not
-following commands. The battery is fine; the site refused to allocate.
-
-**Why it is not fixed here.** The fix is to change what the site loop's target
-*means* while a unit is pinned — regulate the meter using only the unpinned
-packs — which is loop and allocator territory and changes the integrator's
-subject. MAINT-05 moves which pack is pinned and nothing else about it. It is
-pinned as a running check (`test_maintenance.py` part 12) rather than left as a
-comment, so it cannot be forgotten or quietly tuned away, and it wants a card of
-its own.
+Found here and pre-existing: below the pin the other pack had to charge, the
+allocator refused it and the site sat at 0 W. Fixed by a site `drain` floor;
+see [[SAFETY-78]] (`DECISIONS/SAFETY-78-drain-at-two.md`).
 
 ## 7. FOUND AND NOT FIXED: `migrate_unit_keys()` has the same hole, and it is a LATCH
 

goodwe_controller/DECISIONS/SAFETY-78-drain-at-two.md

@@ -0,0 +1,44 @@
+# SAFETY-78 - a maintenance drain at two inverters
+
+**Status: DECIDED 2026-09-29.** Fixes MAINT-05 §6 (OPT-11 P1 F1, UX-13 P3
+check 5, OPT-11 P3 F4). Tests: `test_safety78.py`.
+
+**The defect.** At N>=2 the drain pins its pack (a unit SET at
+`P_MAINTENANCE`) and the site target is split around the pin. Whenever the
+site target was below the pin, the other pack had to charge. The allocator
+refuses opposite directions (SAFETY-25 §0a, SAFETY-31), so the site went to
+0 W and logged `ARBITER: REFUSED` every cycle. That covers a house below the
+drain rate, a grid-charge trade, and a house above it too: after a refusal the
+loop restarts from 0 W and its 400 W slew step is below the pin again.
+
+**The fix.** While a pack drains at N>=2, main.py files a site limit
+`drain`, `lo` = what the pin really places (`allocator.pin_w()`: the drain
+rate inside that pack's own hard limits), at `P_MAINTENANCE`. So the site
+target is never below the pin and the other pack only adds power in the same
+direction. Opposite splits stay forbidden.
+
+- The order is the arbiter's own: a safety SET (100) outranks the limit and
+  the pin, so everything parks; the peak floor (50) and the drain floor are
+  both applied, so the higher wins; a trade or the loop below the drain is
+  lifted to it.
+- Below the drain rate the drained pack exports the rest, as the drain does at
+  N=1 (`maintenance.py`: "forced discharge, exports the surplus"). Holding it
+  to the house load would make N=2 drain differently from N=1; that is an
+  owner question, not this fix.
+- A draining pack that can place nothing (a refusal, a stale link) adds no
+  floor, and the wait is logged once per episode.
+- With battery modes on, no pack is a grid charger while another drains
+  (`modetrade.decide(draining=)`, why `cycle`), and the other battery's card
+  says why (`other_cycle`). Not while the drain waits: no floor is filed
+  then, so the other battery may charge from solar.
+- Not filed at N=1, where the drain is the site SET itself: byte-identical
+  (`tools/safety78_identity.py`, which hashes the claims too).
+
+**Not changed (measured in the PR #154 review, follow-ups).**
+- At N=1 a drain (60) outranks the peak floor (50), so the guard does not add
+  to it: a 5000 W house imports 3000 W against a 2500 W limit, a 6000 W house
+  4000 W. Pre-existing, kept by the N=1 identity.
+- At N=2 a maintenance CHARGE in a cheap window has the same stall: the
+  charging pack's `hi = -floor` against the loop asking the other to give is
+  refused on 141 of 261 cycles. The mirror fix is a site `hi`, which can meet
+  the peak floor's `lo` (0 W), so it is not this card.