SAFETY-95: N=1 identity for every drain end; plainer DOCS line

test_safety95.py: the N=1 byte-identity now covers all six drain ends
(Off and stale link were missing); end_at()/measure() read through a
default, so test_named_absence.py passes (it failed on bdec66e); a check
that a dropped battery's start is 0 W even under a pinned charge (it
kills a mutation that survived).

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

goodwe_controller/DOCS.md

@@ -1702,9 +1702,9 @@ When a charge ends, the other batteries take over one slew step a cycle,
 and none starts charging from the grid (SAFETY-93).
 When a battery's link drops, the others take over one slew step a cycle,
 and control does not stall on the dropped battery's power (SAFETY-96).
-When a drain ends (done, Off, timeout, abort, link, refusal), the others
-cover the house at once but never take over its export; from there control
-moves one slew step a cycle (SAFETY-95).
+When a drain ends (done, Off, timeout, abort, lost link, refused), the
+other batteries cover the house at once but do not export its drain; then
+they move one slew step a cycle (SAFETY-95).
 
 #### Capacity-tariff exposure of the grid-following loop