SAFETY-52: a battery that refuses is asked for 0 W, with a 200 W probe every 15 min

At the BMS cut-out the saturation freeze held the last request for hours
(+5000 W for 11.87 h on 09-06, +1940 W for 3 h 55 m on 09-19) until the grid
error changed sign. compute() now carries a refused direction: after
SETTLE_CYCLES of a ~0 W reading against a larger ask it holds that direction
at 0 W, probes 200 W (below the gate's 250 W) every 15 minutes, and lets go
on charge, an answered probe, stop/start or another writer. A stale-reading
trip on a frozen ~0 W reading seeds the same hold, which ends SAFETY-59's
~70 s cycle. One inverter only; no SoC in the loop (SAFETY-25 Option A).

test_refusal.py drives the real Controller and gate; tools/replay_refusal.py
replays the 16-day capture. test_clamp.py and test_delivery.py re-baselined
where they asserted the old hold. DECISIONS/SAFETY-52 has the record and what
SAFETY-58/59 must take into account.

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

goodwe_controller/app/control.py

@@ -265,6 +265,30 @@ _SAT_COUNT_CAP = SETTLE_CYCLES + 1                           # 13
 # `slew_limit_w()` and therefore with the rail.
 SLEW_LEAD_STEPS = 1
 
+# ---------------------------------------------------------------------------
+# SAFETY-52. A BATTERY THAT REFUSES IS ASKED FOR 0 W, NOT HELD AT ITS LAST ASK.
+#
+# At the BMS cut-out the pack delivers ~0 W whatever it is asked, so the
+# saturation freeze below holds the command where it stood (the recorded
+# 09-06 case: +5000 W for 11.87 h) until the grid error changes sign. The
+# freeze's own exit cannot help: a reading of ~0 against a large ask is inside
+# the interval a limit can produce. So a refused DIRECTION is held at 0 W,
+# carried between cycles like `sat_count`, and left again when the loop wants
+# the other direction, when a small probe is answered, or when the caller
+# resets it (stop, start, another writer). The record is DECISIONS/SAFETY-52.
+#
+# PROBE_W is below freshness.MOVE_W (250 W) on purpose: a probe that small can
+# never arm the stale-reading gate, so it cannot start the gate's ~70 s cycle.
+# test_refusal.py pins the inequality. The cadence and length are the owner's
+# 2026-09-27 answer (every 15 minutes) and freshness.BATT_OBLIGED_S twice over
+# (17 s is how long a healthy reading needs to show a command).
+REFUSED = "battery refuses"
+PROBING = "battery probe"
+PROBE_W = 200.0
+PROBE_ANSWER_W = PROBE_W / 2
+PROBE_EVERY_S = 900.0
+PROBE_S = 34.0
+
 
 @dataclass(frozen=True)
 class Tuning:
@@ -346,6 +370,9 @@ class Decision:
     i_bound_w: float = 0.0
     requested_w: float = 0.0
     clamped_w: float = 0.0
+    # SAFETY-52. The refused direction to carry back in (+1 discharge, -1
+    # charge, 0 none), or None when the caller does not carry it.
+    refused: int | None = None
 
 
 def slew_limit_w(tuning: Tuning) -> float:
@@ -442,6 +469,8 @@ def compute(
     tuning: Tuning,
     sat_count: int = 0,
     i_w: float | None = None,
+    refused: int | None = None,
+    probe: bool = False,
 ) -> Decision:
     """One control cycle. A cycle is one meter update (~5 s on a HomeWizard P1).
 
@@ -449,6 +478,9 @@ def compute(
     `grid_w`   net grid power, + = importing
     `actual_w` what the inverter reports it is doing, + = discharging
     `i_w`      the carried integrator, or None to seed it from `prev_w`
+    `refused`  SAFETY-52's carried refused direction, or None to leave it out
+               (the `i_w=None` equivalence path does)
+    `probe`    the caller's clock says a refused direction may try PROBE_W now
     """
     reason = "tracking"
 
@@ -739,6 +771,26 @@ def compute(
             target = min(target, prev_w) if prev_w > 0 else max(target, prev_w)
             reason = "saturated-freeze"
 
+    # --- SAFETY-52: a refused direction is held at 0 W ----------------------
+    # Engages only where the freeze has held for SETTLE_CYCLES and the unit
+    # delivers ~nothing: a reading within `saturation_w` of 0 against an ask
+    # beyond it is a refusal, not a slow plant. The drop to 0 skips the slew
+    # limit because it only removes an ask the battery is not meeting.
+    if refused is not None:
+        if (refused == 0 and frozen and sat_count >= SETTLE_CYCLES
+                and abs(prev_w) > tuning.saturation_w
+                and abs(actual_w) < tuning.saturation_w):
+            refused = 1 if prev_w > 0 else -1
+        if refused and refused * i_w < 0:
+            refused = 0                          # the loop wants the other way
+        elif refused and probe and refused * actual_w >= PROBE_ANSWER_W:
+            refused = 0                          # the probe was answered
+        elif refused:
+            wants = refused * i_w > 0
+            i_w = 0.0
+            target = refused * PROBE_W if probe and wants else 0.0
+            reason = PROBING if probe and wants else REFUSED
+
     # --- quantise ----------------------------------------------------------
     # 10 W. The register is 1 W and the inverter reports at 1 W, but its
     # response lands on a coarser ladder (~17.6 W measured at ~900 W, consistent
@@ -749,7 +801,7 @@ def compute(
 
     return Decision(float(target), sat_count, frozen, reason, float(i_w),
                     i_clamped, clamped, float(i_bound_w), float(want),
-                    float(clamped_w))
+                    float(clamped_w), refused)
 
 
 def maintenance_charge_floor(