SAFETY-97: "gives nothing" is graded against each battery's idle reading

B's power reading shows -95 to -118 W at idle (standby draw), so the
|reading| < 100 W refusal band never held a refusing B: never at N=2,
and since SAFETY-94's shared rule not at N=1 either (review F1).

Each unit now learns its idle reading (app/idle.py): only while control
runs, the unit is not refused/stale/tripped and its command has stayed
within 50 W for 120 s; first value a 120 s mean, then a 30 min follow;
samples beyond 250 W dropped, value clamped to 250 W; saved per unit and
restored. The shared refusal evidence, compute()'s N=1 engage and end,
the unit refusal ends, the stale-path refusal and SAFETY-42's "parked"
test are centred on it. Until learned it is 0 W, the rule as it was.

Refusing B caught at N=1 28/28/65 s and N=2 24/24/60 s (1/2/5 s
meters), before never; refusing A unchanged. Healthy B with its offset,
SAFETY-94's scenarios, 96 runs: 0 stale, 0 refused. Live replay: 0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019DBUfvndgHwaV339Fvd2gr

goodwe_controller/app/idle.py

@@ -0,0 +1,83 @@
+"""SAFETY-97: what a battery's power reading shows while it gives nothing.
+
+B's reading (0x0518) shows -95 to -118 W at idle (standby draw, live
+2026-10-03); A's shows -2 to -4 W. "The battery gives nothing" is graded
+against this idle reading, not against 0 W, or a refusing B never latches.
+DECISIONS/SAFETY-97-idle-offset.md.
+
+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;
+- 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.
+"""
+
+import math
+
+IDLE_MAX_W = 250.0      # |idle| bound: a band centred further out hides too much
+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
+IDLE_TAU_S = 1800.0     # then follow drift this slowly
+IDLE_SAVE_W = 5.0       # persist when the value moved this far
+IDLE_GAP_S = 10.0       # a longer gap between reads counts as this
+
+
+def _num(v):
+    try:
+        v = float(v)
+    except (TypeError, ValueError):
+        return None
+    return v if math.isfinite(v) else None
+
+
+class IdleReading:
+    """One unit's idle reading. `w` is what "gives nothing" is centred on."""
+
+    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)))
+        self.saved = self.value
+        self.quiet_since = None
+        self.last = None
+        self.acc_w = 0.0
+        self.acc_s = 0.0
+
+    @property
+    def w(self) -> float:
+        return 0.0 if self.value is None else self.value
+
+    def observe(self, reading, standing_w, now_mono, may_learn) -> bool:
+        """One read. Returns True when the value should be persisted."""
+        now = float(now_mono)
+        dt = (0.0 if self.last is None
+              else max(0.0, min(IDLE_GAP_S, now - self.last)))
+        self.last = now
+        standing = _num(standing_w)
+        if not may_learn or standing is None or abs(standing) > IDLE_ASK_W:
+            self.quiet_since = None
+            return False
+        if self.quiet_since is None:
+            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):
+            return False
+        if self.value is None:
+            self.acc_w += b * dt
+            self.acc_s += dt
+            if self.acc_s < IDLE_FIRST_S:
+                return False
+            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
+        return False