SAFETY-107: a refusal held under another writer is learned once (#183)

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

goodwe_controller/DECISIONS/SAFETY-107-refusal-under-another-writer.md

@@ -0,0 +1,96 @@
+# SAFETY-107 - a refusal held under another writer is learned once
+
+**Status: for review.** Tests: `test_safety107.py`. One inverter only; nothing
+changes at N>1 (SAFETY-73's unit refusal has no "another writer" end).
+
+**The defect** (MAINT-13 F5, MAINT-14 "seen again"). A full pack under a
+maintenance charge in a cheap window takes no charge. At N=1 the action log then
+showed "BATTERY REFUSES asked -2500 W ..." and "BATTERY REFUSES ENDED: another
+writer" every cycle: 548 + 548 lines in 15 min on the MAINT-13 rig head,
+652 + 651 in 12 min on its base, 33 + 32 in 60 s in MAINT-14's c2b. The 40-line
+log flooded and the hint under the buttons changed every second, so the
+MAINT-13 notice was gone at once.
+
+**Cause** (`main.py`, the SAFETY-52 block before `compute()`). The end tested
+`self.target != self.loop_w`: the wire differs from the loop's ask. A held
+refusal makes the loop ask 0 W, so any claim that binds (the maintenance
+charge's `hi`, the peak guard's `lo`, a trade's SET) differs from it on every
+cycle. The refusal was ended against the same writer it had been learned
+against. `sat_count` is not reset by that end, so `compute()` learned the same
+refusal again in the same cycle. Nothing about the battery or the wire had
+changed; only the log and the hint did.
+
+**Other writers.** The same flap comes from any writer that holds the wire
+while the loop is refused, as long as the evidence lasts: a trade (a SET at
+P_ARBITRAGE) into a full pack, and the peak guard over an empty pack: 335
+refusal lines in 15 min each at a 5 s meter (`test_safety107.py` part 2, run on
+release/1.0).
+A maintenance drain or hold does not flap: its SET resets `sat_count` each cycle.
+
+**The rule** (`_refusal_update()`, `rejudged`). When another writer held the
+wire, the held refusal is judged afresh: `compute()` gets `refused=0` and no
+probe, exactly as before the change. Then:
+
+1. it finds the same refusal against that writer's ask: the same episode
+   continues, with no line and no hint. The probe clock restarts, as it did on
+   the old end and start: a probe is the loop's ask, and it is not on the wire
+   while another writer is;
+2. it does not: the refusal ends, logged "another writer", or "the battery
+   gives power" when the reading shows it (it was "another writer" before);
+3. it finds the other direction: end, then a new start, as before. In
+   practice 2 comes first: SAFETY-94's evidence restarts when the ask changes
+   sign, so a writer that turns round ends the refusal at once and the other
+   way is learned ~12 cycles later (`test_safety107.py` part 3e).
+
+**Why this rule.** The end now means what SAFETY-52 meant by it: the refusal no
+longer describes what is on the wire, judged by the same test that learns it.
+`compute()` sees the same inputs as before and the state after each cycle is
+the same (`batt_refused`, `batt_refused_at`), so every command is unchanged.
+Keeping the held refusal into `compute()` instead (mutation M5) would also
+stop the lines, but it holds the loop at 0 W where the old law let it ask past
+a writer's limit, which changes commands; it also removes SAFETY-52's
+owner-decided "another writer" exit.
+
+**Evidence.**
+- Differential trace (`goodwe/scratch/SAFETY-107/probe/trace.py`, not in this
+  repo; the real Controller in the CI image, release/1.0 bf3ac79 against this
+  tree): 300 seeds, N=1 (153) and
+  N=2 (147), 1/2/5 s meter, full/empty/dead/healthy battery windows, a stepping
+  house, maintenance charge with the cheap window opening and closing, P1 and
+  the peak guard, trade windows, stop/start; 427 680 cycles, 294 seeds with a
+  refusal held. Every command, site target, integrator, `sat_count`, refusal
+  state and reason is identical. Refusal lines: 100 748 before, 2 188 after.
+- The card's case: 1 line in 15 min at N=1 and N=2, 1/2/5 s meter, house
+  importing or exporting (release/1.0: 335-1 753 at N=1; N=2 was already 1).
+
+**Mutations** (`tools/mutation_run.sh` on purged copies; reds in
+test_safety107 / test_refusal / test_refusal_units; trace = seeds of 300 whose
+commands differ from release/1.0):
+
+| | mutation | reds | trace |
+|---|---|---|---|
+| M1 | `now == rejudged` -> `False` (every such cycle ends: the old flap) | 26 / 0 / 0 | 0 |
+| M2 | `rejudged` always 0 (another writer never ends it) | 5 / 1 / 2 | 29 |
+| M3 | the probe clock is not restarted on a continued episode | 1 / 0 / 0 | 2 |
+| M4 | a probe may open while rejudged | 0 / 0 / 0 | 0 |
+| M5 | the held refusal goes into `compute()` while rejudged | 2 / 1 / 2 | 27 |
+| M6 | an end while rejudged always says "another writer" | 1 / 0 / 0 | 0 |
+
+M4 is equivalent: a probe matters only if `compute()` engages in that call,
+which needs `SETTLE_CYCLES` saturated against the writer, and each of those
+cycles restarted the clock. The line stays because it states the rule.
+
+**Cost.** None in power. A takeover by a different writer while the battery
+still refuses is logged as an end and, ~12 cycles later, a new start against
+that writer (3 lines for the episode, `test_safety107.py` part 3a).
+
+**Not covered.**
+- A perfectly flat reading under a writer. The stale-reading gate trips, stops
+  the site and seeds the refusal (SAFETY-52 decision 3). After the stop the
+  writer's ask returns fresh, `compute()` has no saturation history against it,
+  so the refusal ends at the first cycle and the next trip seeds it again: 2
+  lines per gate cycle (29 in 15 min, house exporting), the same as release/1.0.
+  The gate cycle itself (0 W, then the writer's ask) is the cause; stopping it
+  changes commands. None of the rig runs showed it: real readings move.
+- At N=1 a refusal shapes only the loop. A writer above it still asks the
+  battery; at N>1 SAFETY-73's P_SAFETY claim binds every writer.

goodwe_controller/DOCS.md

@@ -605,6 +605,10 @@ still moving towards the request, such as one turning from charging to
 giving (SAFETY-94). "Gives" is counted from what the battery's reading shows
 at rest, which the add-on learns after two quiet minutes and keeps: some
 inverters show about -100 W at rest (SAFETY-97).
+While another task sets the power, such as a maintenance charge, the peak
+guard or a trade, the refusal stays as long as the battery still refuses that
+task's request. It is logged once, and the 200 W test waits until control sets
+the power again (SAFETY-107).
 
 **With two or more inverters** the same rule works per inverter. An inverter
 whose battery gives less than 100 W for 12 cycles, and at least 22 s, while
@@ -618,7 +622,7 @@ If the battery refuses to give power while its level reads above its “Battery
 cut-out level”, the log adds one warning ending in `REFUSES_ABOVE_CUT_OUT`: check that setting.
 A battery that refuses is not reported as *not delivering*.
 
-*For installers:* SAFETY-52 and SAFETY-73. The event log reads
+*For installers:* SAFETY-52, SAFETY-73 and SAFETY-107. The event log reads
 `BATTERY REFUSES …` and `BATTERY REFUSES ENDED …` (with the inverter's name at
 N>1), and the INFO line ends in `BATTERY_REFUSES`.
 `DECISIONS/SAFETY-52-a-battery-that-refuses.md` has the replay figures and

goodwe_controller/app/main.py

@@ -1279,9 +1279,26 @@ class Controller:
         _LOG.info("The battery refusal ends, control asks for power again: %s.",
                   why)
 
-    def _refusal_update(self, decision, asked_w, batt_w, probe) -> None:
+    def _refusal_update(self, decision, asked_w, batt_w, probe,
-        """Follow `compute()`'s carried refused direction, and say so."""
+                        rejudged: int = 0) -> None:
+        """Follow `compute()`'s carried refused direction, and say so.
+
+        `rejudged`: the refusal held while another writer had the wire, so
+        `compute()` judged it afresh against that writer's ask (SAFETY-107).
+        """
         now = decision.refused or 0
+        if rejudged:
+            if now == rejudged:
+                # Still refused against the ask on the wire: the same episode.
+                # The probe clock restarts, as it did when this was an end and
+                # a new start: a probe is the loop's ask, and it is not on the
+                # wire while another writer is.
+                self.batt_refused_at = self._now_mono
+                return
+            gave = (rejudged * (batt_w - self._site_idle_w())
+                    >= _ctl.PROBE_ANSWER_W)
+            self._refusal_end("the battery gives power" if gave
+                              else "another writer")
         if now and not self.batt_refused:
             self._refusal_start(now, f"asked {asked_w:+.0f} W, the battery "
                                      f"gave {batt_w:+.0f} W for "
@@ -4973,11 +4990,15 @@ class Controller:
             if trade_was and not mode_trade:
                 self._reseed_run_edge(claims)
             # SAFETY-52: another writer overrode the loop, so a refusal learned
-            # against the loop's own ask no longer describes the wire. A gap
+            # against the loop's own ask may no longer describe the wire. A gap
             # (`loop_w` None: blind or stopped) keeps it: the stale-reading stop
             # is what seeds it, and dropping it there restarts the ~70 s cycle.
+            # SAFETY-107: it ends only if compute() no longer finds it against
+            # that writer's ask (`_refusal_update()`). A held refusal makes the
+            # loop ask 0 W, so any claim that binds differs from it every cycle.
+            rejudged = 0
             if self.loop_w is not None and self.target != self.loop_w:
-                self._refusal_end("another writer")
+                rejudged = self.batt_refused
             # SAFETY-96: a battery that dropped out of the split leaves the
             # loop's start point (SAFETY-93's own if its charge ended too).
             self._reseed_drop(_live96)
@@ -4986,7 +5007,8 @@ class Controller:
             # SAFETY-95: then a drain that ended, last (it reads the start
             # the others left).
             self._reseed_drain_end(maint_results, _live96)
-            probe = self._refusal_probe()
+            # No probe while it is judged afresh (the loop does not hold the wire).
+            probe = False if rejudged else self._refusal_probe()
             if len(self.inverters) > 1:
                 probe = any(_probing.values())
             # ⚠️ `actual_w` IS THE SITE SUM AND THAT IS DEV-02's OTHER HALF.
@@ -5029,7 +5051,8 @@ class Controller:
                 # limit already closes an empty battery's discharge end.
                 # SAFETY-73: at N>1 the site law holds 0 W only while every
                 # unit refuses the same way. Otherwise None, the old law.
-                refused=self.batt_refused if len(self.inverters) == 1
+                refused=(0 if rejudged else self.batt_refused)
+                if len(self.inverters) == 1
                 else self._site_refused(),
                 probe=probe,
                 # SAFETY-94: at N=1 the engage also needs the reading to have
@@ -5055,7 +5078,8 @@ class Controller:
             self.loop_w = decision.target_w
             self._loop_decision = decision
             if len(self.inverters) == 1:
-                self._refusal_update(decision, loop_prev, site_batt, probe)
+                self._refusal_update(decision, loop_prev, site_batt, probe,
+                                     rejudged)
             # --- TEL-10 ------------------------------------------------------
             # ⚠️ THE INTEGRATOR HAS NEVER LEFT THIS PROCESS, AND THAT IS WHAT
             # THE CARD IS. `self.i_w` is carried between cycles and published

goodwe_controller/test_safety107.py

@@ -0,0 +1,307 @@
+"""Runnable check for SAFETY-107: a refusal held while another writer has the
+wire is learned once. `python3 test_safety107.py`
+
+A full pack under a maintenance charge in a cheap window took no charge. At
+one inverter SAFETY-52's "another writer" end then fired every cycle, and
+compute() learned the refusal again in the same cycle: "BATTERY REFUSES" and
+"BATTERY REFUSES ENDED: another writer" each second on the rig (MAINT-13 F5).
+Now another writer ends a refusal only if compute(), judging it afresh
+against that writer's ask, no longer finds it. DECISIONS/SAFETY-107.
+
+Drives the REAL Controller (read_inputs + cycle) on opt11_identity's rig.
+1. The card's case: 15 min of a full pack under a maintenance charge, N=1
+   and N=2, at a 1, 2 and 5 s meter: at most 2 refusal lines, held throughout.
+2. Other writers: a trade and the peak guard over a battery that gives
+   nothing. One episode each, no flap.
+3. A refusal still ends: a different writer really takes over, the battery
+   delivers again, a writer asks the other way, stop. The probe clock.
+
+4. Not covered, pinned: a perfectly flat reading under a writer.
+
+Mutations (MUTATION.md, purged copies) are listed in DECISIONS/SAFETY-107.
+"""
+
+import functools
+import logging
+import os
+import sys
+import tempfile
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, HERE)
+sys.path.insert(0, os.path.join(HERE, "tools"))
+logging.disable(logging.WARNING)
+
+import opt11_identity as rig                                   # noqa: E402
+import safety79_identity as s79                                # noqa: E402
+import app.main as app_main                                    # noqa: E402
+from app import control                                        # noqa: E402
+from app.arbiter import Claim, P_ARBITRAGE                     # noqa: E402
+from app.main import Controller                                # noqa: E402
+from named_absence import nth, present                         # noqa: E402
+
+fails = []
+QUARTER = 900.0
+
+
+def check(name, cond):
+    print(f"  {'ok  ' if cond else 'FAIL'} {name}")
+    if not cond:
+        fails.append(name)
+
+
+def run(n=1, *, plant, house, dur=QUARTER, tick=5.0, maint=True,
+        cheap=lambda c, t: True, trade=lambda t: None, p1=False, cap=2500,
+        auto=lambda t: True):
+    """Rows (t, commands, site target, loop reason, refused, refused_at,
+    unit refusals) and every action-log line as (t, line, hint).
+
+    `plant(u, t, cmd)` is battery u's reading. `cheap(c, t)` opens the cheap
+    window. `trade(t)` is a SET claim at P_ARBITRAGE added to the claim list
+    (a writer above the loop), or None."""
+    log, rows, now = [], [], [0.0]
+    real_power, real_tick = rig._Hass.power, rig.TICK
+    real_log, real_resolve, real_c = (Controller.log_event, app_main.resolve,
+                                      rig.Controller)
+
+    def power(self, u):
+        return float(plant(u, self.t, self.cmd[u]))
+
+    def log_event(self, msg, hint=None):
+        log.append((now[0], msg, hint))
+        return real_log(self, msg, hint)
+
+    def resolve(claims, **kw):
+        v = trade(now[0])
+        if v is not None:
+            claims.append(Claim.set("arbitrage", P_ARBITRAGE, v, "trade"))
+        return real_resolve(claims, **kw)
+
+    def before(c, t):
+        now[0] = t
+        if not getattr(c.hass, "_s107", False):
+            read = c.hass.number
+
+            async def number(e, invert=False):
+                if e == "sensor.pnow":
+                    return 0.05 if cheap(c, c.hass.t) else 0.30
+                if e == "sensor.pavg":
+                    return 0.20
+                return await read(e, invert)
+            c.hass.number, c.hass._s107 = number, True
+        if p1:
+            s79._feed(c, t)
+        c.auto = auto(t)
+
+    def on_cycle(c, t):
+        rows.append((t, tuple(c.hass.cmd[u] for u in "ab"[:n]), c.target,
+                     c.loop_reason, c.batt_refused, c.batt_refused_at,
+                     tuple(i.refused for i in c.inverters)))
+
+    extra = {"price_now_entity": "sensor.pnow",
+             "price_avg_entity": "sensor.pavg"}
+    if maint:
+        extra.update({"maintenance_enabled": True,
+                      "maintenance_start_hour": 11,
+                      "maintenance_charge_w": 2000})
+    if p1:
+        extra.update(s79.P1, peak_cap_w=cap)
+    db = os.path.join(tempfile.mkdtemp(prefix="s107-"), "tariff.db")
+    rig._Hass.power, rig.TICK = power, tick
+    Controller.log_event, app_main.resolve = log_event, resolve
+    rig.Controller = functools.partial(real_c, peak_db_path=db)
+    try:
+        _, c = rig.run(n, extra=extra, dur=dur, load=house,
+                       soc=lambda u, t: 50.0, cut=lambda u, t: False,
+                       before=before, on_cycle=on_cycle,
+                       store=s79.store_charging(n) if maint else rig._Store())
+    finally:
+        rig._Hass.power, rig.TICK = real_power, real_tick
+        Controller.log_event, app_main.resolve = real_log, real_resolve
+        rig.Controller = real_c
+    return rows, log, c
+
+
+def full_a(u, t, cmd):
+    """A takes no charge (a full pack), its reading jittering by a few watts
+    as a real one does; B follows."""
+    return -1.0 - int(t) % 3 if u == "a" and cmd < 0 else round(cmd)
+
+
+def flat_a(u, t, cmd):
+    """`full_a` with a perfectly flat reading (the stale-reading gate trips)."""
+    return -1.0 if u == "a" and cmd < 0 else round(cmd)
+
+
+def empty_a(u, t, cmd):
+    """A gives nothing (an empty pack), its reading jittering by a few watts
+    (SAFETY-73's jitter shape, so the stale-reading gate stays out of it);
+    B follows."""
+    return -4.0 - int(t) % 3 if u == "a" and cmd >= -4.0 else round(cmd)
+
+
+def lines(log, word="REFUSES"):
+    return [x for x in log if word in x[1]]
+
+
+def ends(log):
+    return [x for x in log if "REFUSES ENDED" in x[1]]
+
+
+def refused(r):
+    """Row r holds a refusal (site at N=1, any unit at N>1)."""
+    return bool(r[4]) or any(r[6])
+
+
+def held_from(rows):
+    """True when, once learned, the refusal is held on every later row."""
+    first = next((k for k, r in enumerate(rows) if refused(r)), None)
+    return first is not None and all(refused(r) for r in rows[first:])
+
+
+# ==============================================================================
+print("1. the card: a full pack under a maintenance charge, 15 min")
+# ==============================================================================
+for n, tick, house in ((n, k, h) for n in (1, 2) for k in (1.0, 2.0, 5.0)
+                   for h in (800.0, -1500.0)):
+    rows, log, c = run(n, plant=full_a, house=lambda t: house, tick=tick)
+    ref = lines(log)
+    tag = f"N={n}, {tick:.0f} s meter, house {house:+.0f} W"
+    print(f"    {tag}: {len(ref)} refusal line(s): "
+          + " / ".join(x[1][:60] for x in ref))
+    check(f"{tag}: at most 2 refusal lines in 15 min (rig: 548 + 548)",
+          1 <= len(ref) <= 2)
+    check(f"{tag}: no end line", not ends(log))
+    check(f"{tag}: learned once and held to the end", held_from(rows))
+    # N=1: the charge's ceiling stays on the wire. N=2: SAFETY-73 closes A
+    # in the refused direction, as before.
+    check(f"{tag}: still in its charge, the wire as before",
+          c.maints[0].phase == "charge"
+          and all(r[1][0] == (-2000.0 if n == 1 else 0.0)
+                  for r in rows[-10:]))
+    # The hint under the buttons is set at most once for the refusal.
+    check(f"{tag}: the refusal hint is set once",
+          sum(1 for x in ref if x[2] is not None) == 1)
+
+# The probe clock: while the charge holds the wire no probe is tried (the
+# loop's ask is not on the wire), so the action log stays quiet.
+rows, log, _ = run(1, plant=full_a, house=lambda t: 800.0, dur=3600.0)
+check("N=1, an hour: still one line, no probe tried under the charge",
+      len(lines(log)) == 1
+      and not any(r[3] == control.PROBING for r in rows))
+
+# ==============================================================================
+print("\n2. other writers: a trade and the peak guard, no flap")
+# ==============================================================================
+# A trade (a SET above the loop) asks a full pack to charge for 15 min.
+rows, log, _ = run(1, plant=full_a, house=lambda t: 800.0, maint=False,
+                   trade=lambda t: -1500.0)
+print(f"    trade into a full pack: {len(lines(log))} line(s)")
+check("a trade into a full pack: learned once, held, no end",
+      len(lines(log)) == 1 and not ends(log) and held_from(rows))
+# The peak guard asks an empty pack to give while the house is over the limit.
+rows, log, c = run(1, plant=empty_a, house=lambda t: 4500.0, maint=False,
+                   p1=True)
+print(f"    peak guard on an empty pack: {len(lines(log))} line(s), "
+      f"guard floor {c.peak_guard.floor_w if c.peak_guard else None}")
+check("the peak guard on an empty pack: the guard holds the wire",
+      c.peak_guard is not None and c.peak_guard.engaged)
+check("the peak guard on an empty pack: at most 2 lines, held to the end",
+      1 <= len(lines(log)) <= 2 and held_from(rows))
+
+# ==============================================================================
+print("\n3. a refusal still ends")
+# ==============================================================================
+# a. Learned by the loop on an empty pack; at 300 s a trade really takes the
+#    wire and asks it to give 2000 W. The refusal was learned against the
+#    loop's ask: it ends, then is learned against the trade, once.
+rows, log, _ = run(1, plant=empty_a, house=lambda t: 2000.0, maint=False,
+                   trade=lambda t: 2000.0 if 300.0 <= t < 900.0 else None,
+                   dur=1200.0)
+e = ends(log)
+print("    " + " / ".join(f"{x[0]:.0f} s {x[1][:45]}" for x in lines(log)))
+check("a different writer takes over: the refusal ends, 'another writer'",
+      len(e) == 1 and "another writer" in e[0][1] and 300.0 < e[0][0] < 320.0)
+check("...and is learned again against the trade, once, and held",
+      len(lines(log)) == 3 and held_from([r for r in rows if r[0] > 400.0]))
+check("...and the loop keeps it when the trade leaves (no line)",
+      all(x[0] < 900.0 for x in lines(log)) and refused(nth(rows, -1)))
+# The writer asks the other way, which the empty pack takes.
+rows, log, _ = run(1, plant=empty_a, house=lambda t: 2000.0, maint=False,
+                   trade=lambda t: -1500.0 if t >= 300.0 else None)
+e = ends(log)
+check("a writer that asks the other way ends it ('another writer')",
+      len(e) == 1 and "another writer" in e[0][1] and present(nth(rows, -1))
+      and not refused(nth(rows, -1)))
+# b. The full pack starts taking charge again under the same writer.
+rows, log, _ = run(1, plant=lambda u, t, cmd: (
+    round(cmd) if t >= 400.0 else full_a(u, t, cmd)), house=lambda t: 800.0)
+e = ends(log)
+print("    " + " / ".join(f"{x[0]:.0f} s {x[1][:45]}" for x in lines(log)))
+check("the battery takes charge again: the refusal ends once, on its reading",
+      len(e) == 1 and "the battery gives power" in e[0][1]
+      and 400.0 <= e[0][0] < 430.0 and present(nth(rows, -1))
+      and not refused(nth(rows, -1)))
+# c. Stop and start still end it.
+rows, log, _ = run(1, plant=full_a, house=lambda t: 800.0,
+                   auto=lambda t: not 500.0 <= t < 520.0)
+e = ends(log)
+check("stopping control still ends it", any("control stopped" in x[1]
+                                            for x in e))
+# d. The probe clock. Learned under the charge; the cheap window closes when
+#    the refusal is 910 s old, and the loop holds the wire (a surplus, so it
+#    wants to charge). The first probe is a full PROBE_EVERY_S after the
+#    window closed, as before: never at once.
+close = [None]
+
+
+def window(c, t):
+    if close[0] is None and c.batt_refused:
+        close[0] = t + 910.0
+    return close[0] is None or t < close[0]
+
+
+rows, log, _ = run(1, plant=full_a, house=lambda t: -1500.0, cheap=window,
+                   dur=3000.0)
+probes = [r[0] for r in rows if r[3] == control.PROBING]
+print("    " + " / ".join(f"{x[0]:.0f} s {x[1][:45]}" for x in lines(log)))
+print(f"    window closed at {close[0]} s, first probe at "
+      f"{probes[0] if probes else None} s")
+check("the refusal carries over to the loop with no line",
+      len(lines(log)) == 1 and held_from(rows))
+check("the first probe after the writer left comes PROBE_EVERY_S later",
+      close[0] is not None and bool(probes)
+      and probes[0] >= close[0] + control.PROBE_EVERY_S - 10.0)
+# e. A writer turns round on a dead pack with no gap. The evidence restarts
+#    on the new sign (SAFETY-94), so the old refusal ends at once and the
+#    other way is learned once, ~12 cycles later.
+rows, log, _ = run(1, plant=lambda u, t, cmd: (
+    -2.0 - int(t) % 3 if u == "a" else round(cmd)), house=lambda t: 2000.0,
+    maint=False, trade=lambda t: 2000.0 if t < 300.0 else -2000.0)
+e = ends(log)
+print("    " + " / ".join(f"{x[0]:.0f} s {x[1][:45]}" for x in lines(log)))
+check("a writer turns round on a dead pack: one end, then the other way",
+      len(lines(log)) == 3 and len(e) == 1 and 300.0 < e[0][0] < 400.0
+      and present(nth(rows, -1)) and nth(rows, -1)[4] == -1)
+
+# ==============================================================================
+print("\n4. not covered: a perfectly flat reading under a writer")
+# ==============================================================================
+# The stale-reading gate trips on a flat reading while the command moves,
+# stops the site and seeds the refusal (SAFETY-52 decision 3). After the stop
+# the writer's ask comes back fresh, compute() has no saturation history
+# against it yet, so the refusal ends at the first cycle and the next trip
+# seeds it again: one pair per gate cycle, as on release/1.0 (the commands
+# are the same; DECISIONS/SAFETY-107 "Not covered"). Pinned so a change shows.
+rows, log, _ = run(1, plant=flat_a, house=lambda t: -1500.0)
+trips = len(lines(log, "STALE inverter"))
+print(f"    flat reading, house -1500 W: {trips} gate trips, "
+      f"{len(lines(log))} refusal lines in 15 min")
+check("flat reading: no per-cycle flap, at most one pair per gate trip",
+      trips >= 1 and len(lines(log)) <= 2 * trips)
+
+print()
+if fails:
+    print(f"{len(fails)} FAILED: " + ", ".join(fails))
+    sys.exit(1)
+print("all SAFETY-107 checks passed")