MAINT-24: keep the refusal probe beside a maintenance charge

The mode trade still lets a SAFETY-73 probe (PROBE_W alone) go on while a pack
is in its maintenance CHARGE phase; test_opt20.py g7 pins it. ch_ch_maint
digest moved (B no longer grid-charges beside A's charge).

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

goodwe_controller/DECISIONS/MAINT-24-charge-first.md

@@ -1,6 +1,6 @@
 # MAINT-24 - a started maintenance charge gets the cheap night
 
-**Status: for review.** Tests: `test_maint24.py`. No option added; the MAINT-13
+**Status: for review.** Tests: `test_maint24.py` (`test_opt20.py`'s `ch_ch_maint` digest moved with it). No option added; the MAINT-13
 timeout numbers are unchanged. Folds in SAFETY-80. SAFETY-111 stays on its card (section 3).
 
 **What happened (live 0.21.0, A, 2026-11-08..11).** A sat in its maintenance
@@ -18,7 +18,9 @@ charging time and ended the cycle. Report: `reports/MAINT-24-investigation-repor
 `modetrade.decide(maint_charging=)`, set in `_mode_roles()` when any pack is in
 its maintenance CHARGE phase. It is the mirror of `draining` (SAFETY-78): no
 grid-charge trade for the other packs, why `cycle`, the same Tick. The other
-packs keep their solar roles, so they may still take spare solar. B's night
+packs keep their solar roles, so they may still take spare solar. A refusal probe
+(SAFETY-73, PROBE_W alone, OPT-20) still goes on: it places no charge on the
+pack in maintenance, and `test_opt20.py` g7 pins it. The drain still blocks it. B's night
 charge waits for the nights A needs. At N=1 the only pack is the one in
 maintenance, so nothing changes.