MAINT-15: the balancing hold ends on time with no SoC reading

HOLD's time check moves into Maintenance._hold(), used by step() and
_no_soc(). A hold that loses its SoC now ends at hold_min, writes
last_completed and logs the same COMPLETE line. The 15 min HOLD line says
the hold still ends at its normal time. Behaviour with a reading is
unchanged (differential trace against db9e231).

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

goodwe_controller/DECISIONS/MAINT-14-no-soc-in-maintenance.md

@@ -58,10 +58,7 @@ allows discharge.
 
 ## What this does not cover
 
-- **HOLD with no SoC** still holds 0 W and, as before, does not end while the
-  reading is missing: its time check sits behind the same early return. A HOLD
-  needs no level to end, so this is a candidate follow-up, not part of this fix. It is card MAINT-15. The "no battery level" line in
-  HOLD says only that the hold waits for the level.
+- **HOLD with no SoC**: closed by MAINT-15 (`MAINT-15-hold-ends-without-soc.md`).
 - It does not tell the operator why the reading is missing (sensor, register,
   link). It does not reuse the stale-input gate; it is the cycle's own rule.
 - The charge itself is still driven by the control loop, which has its own

goodwe_controller/DECISIONS/MAINT-15-hold-ends-without-soc.md

@@ -0,0 +1,43 @@
+# MAINT-15 - the balancing hold ends on time with no SoC reading
+
+**Status: for review.** Tests: `test_maint15.py`. No option added.
+
+**The fault.** `step()` sent every tick with no SoC to `_no_soc()`, and for
+HOLD that returned 0 W without the time check. A hold that lost its reading
+never ended: `last_completed` was never written and the next due date never
+moved. Harmless for power (0 W), but the cycle was stuck. This was left open
+in MAINT-14.
+
+## Rule
+
+1. **HOLD ends at `hold_min` whether or not there is a reading.** One helper,
+   `Maintenance._hold()`, holds the time check and is used by both paths. When
+   the time is up it writes `last_completed`, goes IDLE and logs the same
+   "cycle COMPLETE" line. Before the time is up it commands 0 W as before.
+2. **Text.** The 15-min "no battery level" line in HOLD now reads "The hold
+   still ends at its normal time." Still once per episode.
+
+## Why
+
+HOLD is reached only after the charge counted as done. Every entry into HOLD
+is in `step()` or `_no_soc()` and follows a charge that reached the target,
+stalled near full (MAINT-13) or timed out near full (MAINT-13/14). Nothing else
+sets the phase to HOLD (`_enter(HOLD` has four call sites, all after a done
+charge). The hold is a wait for the BMS to balance; it never needed the level.
+So a hold that ends with no reading is a completed cycle. The "cycle COMPLETE"
+line is true without a reading: it names minutes of hold, not a level.
+
+## Cost
+
+- If the level was lost during the hold, the cycle is recorded as complete
+  without anyone seeing the final level. The charge had counted as done, so this
+  is the same trust MAINT-14 already gives a charge that ends with no reading.
+
+## What this does not cover
+
+- It does not check that the pack is still full at the end of the hold.
+- It does not say why the reading was lost.
+- With a reading, nothing changes (proved by a differential trace against
+  release/1.0 in `test_maint15.py`).
+- A state file written by an older version with `phase: hold` loads and ends on
+  time; the file is not changed in format.