MAINT-14: maintenance with no SoC reading: charge times out, drain holds at 0 W

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

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

@@ -0,0 +1,70 @@
+# MAINT-14 - no SoC reading in a maintenance cycle
+
+**Status: for review.** Tests: `test_maint14.py`. No option added; the one new
+number is a constant in `app/maintenance.py`.
+
+**The fault.** `Maintenance.tick()` returned early when the SoC was `None`,
+before any timeout check. (1) A charge on a pack whose SoC reading was lost
+never ended: no timeout, no back-off, no notice, and the 7-day backstop of
+MAINT-13 sat behind the same return. (2) A drain kept commanding `discharge_w`
+with an unknown level, which breaks the TEL-08 rule that an unknown level never
+allows discharge.
+
+## Rules
+
+1. **Charge, no SoC.** The charge timeout (`CHARGE_TIMEOUT_MIN`, gate-open
+   minutes) and the 7-day wall backstop still run. When one fires: if the last
+   SoC seen was >= target - 3 the charge counts as done (the MAINT-13 "close
+   enough to full" rule, HOLD follows); otherwise it fails: MAINT-13 back-off
+   and its one notification. If no SoC was ever seen, it fails.
+2. **Drain, no SoC.** DRAIN holds at 0 W and owns the setpoint, exactly as HOLD
+   does. The 12 h drain timeout still runs and fails as before.
+3. **SoC comes back.** Nothing is recorded; the drain continues at the drain
+   rate, the charge carries on, and the stall wait of MAINT-13 restarts from
+   what it was: it paused while the reading was missing, so a gap never counts
+   as "no more charge".
+4. **HOLD** is unchanged (0 W).
+5. **Log.** One line when a drain starts holding for this reason ("the battery
+   level is unknown, so the drain holds at 0 W until it is back"), and one line
+   when the level has been missing for `NOSOC_NOTE_MIN` = 15 min. Both are said
+   once per episode; the old line that repeated every tick is gone.
+
+## Why
+
+- **"Last seen", not "best seen".** A pack that was at 99 and then dropped to 50
+  before the reading went is not close to full. Only the last reading counts.
+  It is saved with the charge record (`charge_track.last`), and saved at once
+  when the reading first goes missing, so a restart mid-gap still knows it
+  (within the usual 5 min save interval otherwise).
+- **Failure when nothing was seen.** With no level we cannot call a pack full.
+  The failure costs a 7-day wait and one notice; calling it done costs a
+  missed balance and a month-long false "complete". The first is the honest one.
+- **Timeouts count the same minutes as with a reading.** Gate-open charging
+  minutes only; the wall backstop for a gate that never opens.
+- **15 min.** A judgement. A poll glitch of a few minutes should not write a
+  line; a reading lost for a quarter of an hour is worth one. Raise it if the
+  action log shows noise.
+- **0 W, not "stop the phase".** Aborting a drain on a short gap would throw
+  away the part already drained. Holding at 0 W loses nothing and the 12 h
+  timeout is the limit.
+
+## Cost
+
+- A drain that loses its reading stops draining, and the 12 h clock keeps
+  running. A gap of many hours can therefore fail a drain that was working. The
+  back-off then applies (7 days).
+- A charge whose reading is lost early (last SoC below target - 3) fails at the
+  timeout, even if the pack was in fact filling. The same 7-day wait applies.
+
+## 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 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
+  handling of a missing SoC (TEL-08 for the loop is a separate card).
+- A restart loses at most 5 min of accounting, as in MAINT-13. The "unknown for
+  long" line may be said again after a restart: the episode start is in memory.
+- Text added is two log lines, English only, like the other log lines.