SAFETY-97: centre the band on the idle reading clamped to 75 W

Owner decision 2026-10-04 (review R1). A wrong idle reading more than
about 100 W off hid every refusal on that battery. Clamped under the band,
the band keeps 0 W +-25 W, so a battery reading about 0 W while refusing is
caught whatever was learned or restored. Samples are still taken to 250 W.
Beyond about +-170 W of idle a battery behaves as in 0.14.0.

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

goodwe_controller/DECISIONS/SAFETY-97-idle-offset.md

@@ -1,8 +1,9 @@
 # SAFETY-97 - "gives nothing" is graded against each battery's idle reading
 
 **Status: implemented 2026-10-04, folded into PR #171 (SAFETY-94), for
-review.** Tests: `test_safety97.py` (rig: `tools/safety94_rig.py`). Closes
-SAFETY-94 review finding F1.
+review.** Owner decision 2026-10-04: the band's centre is clamped to
++-75 W (see Bounds). Tests: `test_safety97.py` (rig: `tools/safety94_rig.py`).
+Closes SAFETY-94 review finding F1.
 
 ## The defect
 
@@ -27,10 +28,11 @@ B sat on the band's edge and never latched:
   than 50 W, and while refused it does not learn, so its refusal cannot be
   learned as idle. A capped battery under a big ask is not sampled either.
 - **How:** the first value is the mean of 120 s of samples; then it follows
-  drift with a 30 min time constant. A sample beyond 250 W (`IDLE_MAX_W`)
-  is dropped (a register held at a giving value); the value is clamped to it.
+  drift with a 30 min time constant. A sample beyond 250 W (`IDLE_SAMPLE_W`)
+  is dropped (a register held at a giving value). The band is centred on
+  the value clamped to 75 W (`IDLE_MAX_W`; owner decision below).
 - **Restart:** saved per unit (`unit/<name>/idle_w`, on first learn and each
-  5 W move) and restored, clamped. Without it a battery refusing from the
+  5 W move) and restored, clamped to 250 W. Without it a battery refusing from the
   start is never quiet, so never learned, so never caught.
 - **Until learned the idle reading is 0 W**: the rule as it was.
 
@@ -70,16 +72,29 @@ Every test of "gives nothing / gives / takes" now uses `reading - idle`:
 | SAFETY-30 per-unit sign | unchanged: opposition needs both over 250 W; B's 100 W idle cannot make or hide one alone |
 | SAFETY-42 shortfall | unchanged: B reads ~100 W short at every power, which errs towards reporting (report only) |
 
-## Bounds
+## Bounds: owner decision 2026-10-04 (review R1)
 
-- Band: `|reading - idle| < 100 W`, `|idle| <= 250 W`.
-- A correct idle reading: a refusing B behaves as a refusing A.
-- A wrong one (worst, 250 W off): a refusing battery reading outside the band
-  is not refused by this rule; a frozen register is still caught by the stale
-  gate at 35 s of asking. Learning only at a ~0 W command for 2 min keeps a
-  wrong value unlikely. Once learned, a 10 min transient moves it by 28 %;
-  the first value (a 2 min mean) is the exposed one.
-- An idle reading beyond 250 W is never learned: such a unit keeps 0 W.
+Band: `|reading - centre| < 100 W`, centre = idle clamped to +-75 W.
+
+- **Why a clamp under the band.** A wrong idle reading (taught during a
+  rest while the reading shows something else, e.g. a grid top-up of a unit
+  held at 0 W, or restored onto a swapped inverter) more than about 100 W off
+  hid every refusal on that battery, at N=1 and N=2; with the first +-250 W
+  clamp the rig missed a refusing A whenever the error was 110-250 W. At
+  +-75 W the band always keeps 0 W +-25 W, so a battery reading about 0 W
+  while refusing is caught whatever was learned or restored, and a wrong idle
+  cannot refuse a healthy 0 W battery (its ask is over 200 W).
+- **The trade-off.** Options: keep +-250 W (covers idle readings to about
+  +-350 W, any 100 W mis-learn hides refusals); clamp to +-75 W (chosen);
+  "old band or centred band" (rejected: a correct B would need to give 200 W
+  to answer its 200 W probe).
+- **Cost.** A battery whose idle reading is beyond about +-170 W is centred
+  at most 75 W out, so its refusal falls outside the band: it behaves as in
+  0.14.0 (not caught by this rule). B (-95 to -118 W) reads 20-43 W from its
+  clamped centre. B is caught across -150..+90 W of error in its idle
+  reading; learned 110 W or more too high it is missed, as in 0.14.0 at N=2.
+- A frozen register is still caught by the stale gate at 35 s of asking.
+- Recovery from a wrong value needs quiet time: tau 30 min.
 
 ## Catch times (rig, refusing from 200 s after a 400 s rest, +-4 W)
 

goodwe_controller/app/idle.py

@@ -9,16 +9,18 @@ Learned per unit, never configured:
 - only while control runs, the unit is not refused, stale or tripped, and
   its command has been within IDLE_ASK_W for IDLE_QUIET_S (a refusing battery
   is asked more than that, so it cannot teach its refusal as idle);
-- a reading beyond IDLE_MAX_W is not a sample, and the value is clamped to it;
+- a reading beyond IDLE_SAMPLE_W is not a sample;
 - first value: the mean of IDLE_FIRST_S of samples; then a slow follow
   (IDLE_TAU_S);
-- persisted per unit and restored, clamped, at start.
-Until learned the idle reading is 0 W, the rule as it was.
+- persisted per unit and restored, clamped to IDLE_SAMPLE_W, at start.
+The band is centred on it clamped to IDLE_MAX_W (owner, 2026-10-04). Until
+learned the idle reading is 0 W, the rule as it was.
 """
 
 import math
 
-IDLE_MAX_W = 250.0      # |idle| bound: a band centred further out hides too much
+IDLE_MAX_W = 75.0       # |idle| used: under the 100 W band, so it keeps 0 W +-25 W
+IDLE_SAMPLE_W = 250.0   # a reading beyond this is not a sample
 IDLE_ASK_W = 50.0       # a command this small counts as "asked ~0"
 IDLE_QUIET_S = 120.0    # 6 lags of 20 s: a 2500 W step has decayed to 6 W
 IDLE_FIRST_S = 120.0    # seconds of samples averaged for the first value
@@ -41,7 +43,7 @@ class IdleReading:
     def __init__(self, saved=None):
         v = _num(saved)
         self.value = (None if v is None
-                      else max(-IDLE_MAX_W, min(IDLE_MAX_W, v)))
+                      else max(-IDLE_SAMPLE_W, min(IDLE_SAMPLE_W, v)))
         self.saved = self.value
         self.quiet_since = None
         self.last = None
@@ -50,7 +52,10 @@ class IdleReading:
 
     @property
     def w(self) -> float:
-        return 0.0 if self.value is None else self.value
+        """The centre used: the learned value clamped to IDLE_MAX_W."""
+        if self.value is None:
+            return 0.0
+        return max(-IDLE_MAX_W, min(IDLE_MAX_W, self.value))
 
     def observe(self, reading, standing_w, now_mono, may_learn) -> bool:
         """One read. Returns True when the value should be persisted."""
@@ -66,7 +71,7 @@ class IdleReading:
             self.quiet_since = now
         b = _num(reading)
         if (now - self.quiet_since < IDLE_QUIET_S or b is None
-                or abs(b) > IDLE_MAX_W or dt <= 0.0):
+                or abs(b) > IDLE_SAMPLE_W or dt <= 0.0):
             return False
         if self.value is None:
             self.acc_w += b * dt
@@ -76,7 +81,6 @@ class IdleReading:
             self.value = self.acc_w / self.acc_s
         else:
             self.value += (b - self.value) * min(1.0, dt / IDLE_TAU_S)
-        self.value = max(-IDLE_MAX_W, min(IDLE_MAX_W, self.value))
         if self.saved is None or abs(self.value - self.saved) >= IDLE_SAVE_W:
             self.saved = self.value
             return True

goodwe_controller/test_safety97.py

@@ -169,7 +169,7 @@ def small_ask():
 b, b_old = small_ask(), without_fix(small_ask)
 check("SAFETY-42: B giving nothing at a small ask, idle -100 W, is parked "
       "(not latched as not delivering in 700 s; with idle 0 W it is)",
-      not b.delivery_wd.tripped and b.idle_w == -100.0
+      not b.delivery_wd.tripped and b.idle.value == -100.0
       and b_old.delivery_wd.tripped)
 
 # ============================================================================ #
@@ -213,8 +213,11 @@ check("⭐ a charge reversing into a discharge (lag 10 and 20 s, 1 s meter) "
 print("\n3. learning the idle reading")
 _t, r = caught(2, "b", 1.0)
 c = r["c"]
-check("learned during the rest: A about 0 W, B about -100 W, and saved",
-      abs(c.inverters[0].idle_w) < 5 and abs(c.inverters[1].idle_w + 100) < 5
+check("learned during the rest: A about 0 W, B about -100 W (used: -75 W), "
+      "and saved",
+      abs(c.inverters[0].idle_w) < 5
+      and abs(c.inverters[1].idle.value + 100) < 5
+      and c.inverters[1].idle_w == -idle.IDLE_MAX_W
       and abs(c.store.data.get(unit_key("inverter-b", "idle_w"), 0) + 100)
       < 5)
 
@@ -250,10 +253,11 @@ try:
 finally:
     rig.Plant = real_plant
 b = r["c"].inverters[1]
-print(f"    refusing B reading -160 W: refused at {_t} s, idle {b.idle_w:.1f}")
+print(f"    refusing B reading -160 W: refused at {_t} s, idle "
+      f"{b.idle.value:.1f}")
 check("⭐ not learned while refused: 800 s held at 0 W reading -160 W leaves "
       "B's idle reading at -100 W",
-      _t is not None and b.refused and abs(b.idle_w + 100.0) < 1.0)
+      _t is not None and b.refused and abs(b.idle.value + 100.0) < 1.0)
 
 # Not learned while control is stopped (another owner may drive the battery)
 # or while the unit's sign watchdog has latched.
@@ -319,12 +323,58 @@ for t in range(0, 600):
 check("a reading beyond 250 W is not a sample (-300 W: never learned; a "
       "register held at 2000 W then -240 W: -240 W)",
       o.value is None and p.value is not None and abs(p.value + 240.0) < 1e-6)
-check("a saved value is clamped to 250 W, and garbage is ignored",
-      idle.IdleReading(900).w == idle.IDLE_MAX_W
+check("a saved value is clamped to 250 W, the band's centre to 75 W, and "
+      "garbage is ignored",
+      idle.IdleReading(900).value == idle.IDLE_SAMPLE_W
+      and idle.IdleReading(900).w == idle.IDLE_MAX_W
       and idle.IdleReading(-900.0).w == -idle.IDLE_MAX_W
+      and idle.IdleReading(-60.0).w == -60.0
       and idle.IdleReading("x").value is None
       and idle.IdleReading(float("nan")).value is None)
 
+# ============================================================================ #
+print("\n3b. a wrong idle reading (owner, 2026-10-04: centre clamped to 75 W)")
+
+
+def wrong_idle(n, unit, err, restore):
+    """Seconds from the cut to the refusal when the idle reading is `err` W
+    off: taught wrong during the rest, or restored wrong."""
+    cu = "a" if n == 1 else unit
+    true = -100.0 if unit == "b" else 0.0
+    if restore:
+        return caught(n, unit, 1.0, store={
+            unit_key(f"inverter-{cu}", "idle_w"): true + err})[0]
+
+    class _W(rig.Plant):
+        def advance(self, t):
+            rig.OFFSET[cu] = true + (err if t < REST else 0.0)
+            super().advance(t)
+    saved, real = dict(rig.OFFSET), rig.Plant
+    rig.Plant = _W
+    try:
+        return caught(n, unit, 1.0)[0]
+    finally:
+        rig.Plant = real
+        rig.OFFSET.clear()
+        rig.OFFSET.update(saved)
+
+
+A_WRONG = {(n, e, rs): wrong_idle(n, "a", e, rs) for n in (1, 2)
+           for e, rs in ((-250.0, False), (-150.0, False), (150.0, False),
+                         (250.0, False), (-250.0, True), (200.0, True),
+                         (250.0, True))}
+print(f"    A (reads about 0 W) refusing, idle off by E: {A_WRONG}")
+check("⭐ a battery reading about 0 W while refusing is caught whatever idle "
+      "reading was learned or restored (A, E -250..+250 W, N=1 and N=2)",
+      all(v is not None and v <= 32.0 for v in A_WRONG.values()))
+check("⭐ ...including a wrong saved idle_w of +200 W on A",
+      all(A_WRONG[(n, 200.0, True)] is not None for n in (1, 2)))
+B_WRONG = {(n, e): wrong_idle(n, "b", e, False) for n in (1, 2)
+           for e in (-150.0, -50.0, 90.0)}
+print(f"    B refusing, idle taught wrong by E: {B_WRONG}")
+check("B is caught across -150..+90 W of error in its idle reading",
+      all(v is not None and v <= 32.0 for v in B_WRONG.values()))
+
 # ============================================================================ #
 print("\n4. the rules at their edges")
 
@@ -378,8 +428,11 @@ check("compute(): a charge refusal ends when the battery takes 100 W more "
       and control.compute(actual_w=-205.0, idle_w=-100.0, **args).refused
       == 0
       and control.compute(actual_w=-110.0, **args).refused == 0)
-check("the idle bound is under the band's reach of a real delivery: 250 W",
-      idle.IDLE_MAX_W == 250.0 and idle.IDLE_ASK_W < control.PROBE_W)
+check("the band's centre stays within 75 W of 0 W, so the band keeps 0 W "
+      "+-25 W; samples to 250 W",
+      idle.IDLE_MAX_W == 75.0 and idle.IDLE_SAMPLE_W == 250.0
+      and control.REFUSED_BELOW_W - idle.IDLE_MAX_W >= 25.0
+      and idle.IDLE_ASK_W < control.PROBE_W)
 
 print()
 if fails: