# SAFETY-31 — what "acted on" means for circulating power, and what it cannot mean **Status: DECIDED 2026-09-04.** The trip **stops the site**: a `SET 0 W` claim at `P_SAFETY` on the **site** actuator, latched, persisted, and re-announced after a restart. This document records why that is an action rather than theatre, given that [[HW-01]] established a wedged inverter cannot be commanded at all — and it records the numbers the threshold and the window were read off, because "establish the window from the rig, do not pick a round number" is an acceptance criterion and a number without its measurement is a guess. Filed with SAFETY-31. Card `6a99e0022b6a6c8ca15dbe3e`. --- ## 0. The two halves, and which one this card built Half of this card was already shipped, and it is not the half below. | | **ALLOC-01, AC 7 — the COMMAND half** | **SAFETY-31 — the MEASUREMENT half** | |---|---|---| | what it is | `allocator.REFUSE_SIGN` | `circulation.circulating_w()` + `CirculationWatchdog` | | what it sees | the shares the allocator is about to hand out | each inverter's **own measured power** (`Inverter.batt`, register 0x0518) | | what it does | **refuses** the allocation, names both units, returns no shares | **stops the site**, latches, alarms durably | | what it covers | circulating power the allocator would have **commanded** | circulating power **nobody commanded** | | graded by | `test_alloc.py` part 6 | `test_watchdog.py`, the SAFETY-31 section | **They are complements, not duplicates.** The gate refuses an allocation before it is written and cannot see one millisecond past that. This card reads the hardware and does not care what was written. Neither replaces the other, and **a sensor built on the allocation record would collapse the second into the first and detect nothing** — see §2. ## 1. What "acted on" means > **The trip files `Claim.set("circulation", P_SAFETY, 0.0)` on the SITE > actuator. Every inverter is commanded 0 W and held there until an operator > starts control again.** ### The objection, which is correct [[HW-01]] is on the record: on 2026-09-02 the comms subsystem failed and the power stage went on executing its last instruction for **6 h 25 m**, through every command this add-on sent it. If the cause of the circulation is a unit that has stopped listening, **a command is not a remedy**, and shipping one as though it were is theatre. ### The answer **A circulating loop needs two participants.** In every cause on this card's list — a unit ignoring its share, a unit lagging it, a stale share still being executed, a maintenance or [[SAFETY-25]] pin holding one unit while the loop drives the other, or HW-01's wedged power stage — **exactly one participant is the unit that stopped listening, and the other one is this controller**, faithfully commanding the sibling to a share computed to sum with a number the wedged unit is not actually producing. Stopping the commanding half does two things a notification cannot: 1. **It halves the loop.** The unit that *is* still listening stops being driven into the one that is not. That is real energy and real cycles off a real pack, and it needs no cooperation from the wedged unit to take effect. 2. **It makes the residue visible — and this is the more important half.** Circulating power hides *because it nets to zero at the meter*. With this controller's contribution removed, whatever the wedged unit is still doing stops being cancelled and appears at P1 as a plain net flow, where SAFETY-02's sign watchdog, the peak guard and the capacity tariff can all see it. **The fault stops being invisible.** Measured on the [[TEST-19]] rig, and this is the number that makes the case: in the card's own scenario — A at −3000 W, B at +3000 W, house load 0 W — the meter reads **+0 W** and the shipped `SignWatchdog`'s predicate is **false on every one of 30 cycles**, because it gates on `abs(grid_w) > 300` and the gate never opens. ### What it does not do, said plainly **It does not stop the wedged inverter. Nothing this add-on can send will.** If the loop persists at the meter after this trip, the remaining actuator is a human at the isolator, and the notification says so in those words. ### Why the claim is SITE-scoped `arbiter.CLAIM_SCOPE` classifies `circulation` as `SCOPE_SITE`, beside `loop`, `peak`, `arbitrage` and `safety`. The neighbouring `failsafe` entry looks like it and is not: SAFETY-02 has site-wide *evidence* and a per-unit *conclusion*, because it compares the meter against the command **this controller put on one actuator**. Circulating power has no such conclusion available. It is `Σ|Bᵢ| − |ΣBᵢ|` — defined over the whole roster, **identically zero for any one unit** — and there is no fact of the matter about which of two opposing inverters is the offender: *a unit ignoring its share* and *a sibling faithfully executing a share computed to sum with it* produce **identical readings**. Filing this per-unit would require inventing an attribution the measurement cannot support, and would park one inverter while the other went on feeding the loop — quite possibly parking the only one still listening. The same argument is why the latch is **flat** in the store (`circ_tripped`, `circ_reason`) and not namespaced like SAFETY-02's. One site, one latch. ## 2. Why the sensor is MEASURED, and why the cheap version is worthless The obvious cheap version computes the same formula over `Allocation.shares`. It would be simpler, would never be `None`, and would be **worth nothing**, for two independent reasons: 1. **It cannot fire.** ALLOC-01's sign-coherence gate already refuses any allocation whose shares carry two signs. A record-derived sensor is therefore a sensor over a set that is **guaranteed sign-coherent**. It reads zero *by construction*, forever. 2. **It is [[MUTATION.md]]'s third failure mode.** It could only ever confirm that the allocator agrees with itself — a check whose data cannot reach the failure it names. Verified rather than argued. On the rig, with inverter B wedged on a stale discharge while PV drives the site to charge: ``` S = -2500 W shares a = -1250 W b = -1250 W <- record: ok, ONE sign, sums to S MEASURED A = -1250 W B = +1000 W <- hardware sensor over the RECORD : 0 W sensor over MEASURED power : 2000 W -> trips at 190 s ``` And the card's own headline scenario, driven on the same rig — A at −3000 W, B at +3000 W, house load 0 W: ``` METER (P1) : +0 W <- the site looks IDLE sensor over MEASURED power : 6000 W -> trips at 100 s SAFETY-02 SignWatchdog : predicate false on 30 of 30 cycles ``` The same pair is asserted in `test_watchdog.py` **with the precondition written as its own check and printed**, per MUTATION.md's rule, and mutation **M10** (the property rewritten to read `self.allocation.shares`) takes it **red**. ## 3. The numbers, and where they come from Both were read off a curve produced on `admin/goodwe`'s `sim/` two-master rig, used read-only: the add-on's own `compute()`, its own `allocator.plan()` and its own `circulating_w()`, driving `plantsim.Plant` through the firmware's own encoder, with the sensor input taken from each unit's holding register 0x0518. **924 closed-loop runs in which nothing is faulty** — every unit executes the share it was given — over both families of stimulus that can produce legitimate opposition (7 reversals × 5 write staggers, and 7 flap periods × 4 amplitudes), each swept across the **whole range `config.yaml` accepts** for the two settings that decide how fast the site can turn around: `gain` `float(0.05,1.0)` and `slew_w` `int(50,5000)`. ### Reproducing it The rig lives in `admin/goodwe` (`sim/`) and was used **read-only**; the harness is not committed here because it imports that repo's `plantsim`/`frame_check`, which are not present in this one or in CI. What it does is small enough to restate: build `Site([Inverter.from_spec("A", INVERTER_A), Inverter.from_spec("B", INVERTER_B)])`, close the loop with the add-on's own `compute()` and `allocator.plan()`, put each share on its unit's wire through `Inverter.command()` (which goes out through the firmware's real encoder), and read the sensor from `inv.reg(0x0518)` — **the same register the live add-on's `batt_entity` binds**, so the input is the one the shipped code gets. Point it at a checkout with `GOODWE_ADDON_REPO`. ⚠️ MUTATION.md's note applies: those harnesses write `__pycache__` into **both** trees, so purge both by hand before grading a mutation through one. Every figure below was re-run against the final shipped `CirculationConfig` (`min_w=700`, `hold_s=75`) rather than against the draft values they were first measured at. ### Worst CONTINUOUS legitimate opposition, by threshold | threshold | worst continuous | runs that ever cross it | |---:|---:|---:| | 100 W | **505.0 s** | 281 / 924 | | 200 W | 445.0 s | 174 / 924 | | 250 W | 40.0 s | 132 / 924 | | 300 W | 10.0 s | 115 / 924 | | **400 W** | **5.0 s** | 74 / 924 | | 700 W | 5.0 s | 33 / 924 | | 1000 W | 5.0 s | 16 / 924 | | 1700 W | 0.0 s | 0 / 924 | ****With the shipped `min_w=700 W` and `hold_s=75 s`, 0 of those 924 runs trip.** The knee is at 400 W and it is sharp.** Below ~250 W a flapping load holds the sensor above the threshold for *minutes* at a time, and no window shorter than the 900 s billing quarter could tell that from a fault. At 400 W and above the worst legitimate episode collapses to **5.0 s — one control cycle — and stays there**. The worst peak on any legitimate run is **1700 W**. That 5.0 s is the serialised write path doing exactly what it should: on a reversing cycle inverter B's new number lands up to a whole control cycle after A's, both then slew through zero at 800 W/s behind a 10 s lag, and **between the two zero crossings they genuinely oppose**. Nothing is wrong. A guard that tripped on it would be the fourth false-alarm generator of the week, and this project's doctrine on crying wolf is explicit ([[SAFETY-15]], [[SAFETY-19]]). ### `circulation_w: 700` — schema floor `400` `700` is **1.75× the measured knee**. The headroom is bought for one named reason: **inverter B does not physically exist.** Its ramp and lag in the rig are inverter A's, *copied*, carrying `measured=False`; [[SPIKE-04]] measures the real ones. A slower or faster second unit moves the transient's shape, and the margin above the knee is what absorbs that without re-opening this card. **Revisit when SPIKE-04 lands, not before.** The **schema floor is the knee itself**, 400 W, so a legally configured install cannot land in the 445–505 s regime. What the threshold costs: a circulating loop smaller than 350 W per unit is not reported, which is deliberate — at that scale the round-trip loss is a few watts. ### `circulation_hold_s: 75` — schema range `30..900` Three bounds, and the value clears all three: * **lower, from the rig — 5.0 s.** The worst continuous legitimate opposition above 700 W across all 924 runs. * **lower, from the firmware — 30 s (`inverter.LINK_STALE_S`).** A unit still executing a stale share for less than the firmware's own veto window is a *link* fault, and the add-on already answers it: liveness drops the unit and the survivors carry its share, with the record saying so. Firing inside that window would raise a second, louder alarm about a state already being handled. * **upper, from the bill — 900 s**, the quarter that sets the capacity tariff. **75 s** is fifteen control cycles: **15× the worst legitimate episode**, **2.5× the firmware veto**, and **12× inside the quarter**. It is deliberately not 60 or 120 — a round number here would be a guess wearing a measurement's clothes, and a check in `test_watchdog.py` asserts it is none of the values a guess lands on. ## 4. Why the window cannot be defeated the way SAFETY-02's was `allocator.py` records the measurement that makes SAFETY-02 blind to the broadcast fight: the sign disagreement **flips on alternate ticks**, so `disagree_since` is cleared between every pair of them and the 180 s hold never accumulates. Circulating power cannot do that. It is a **magnitude**, non-negative by construction, and a sustained loop holds it high on *every* cycle rather than every other one. An oscillation that genuinely alternated between opposing and agreeing is not a circulating loop and should not be reported as one — which is exactly the flapping-load case in §3, and it is why the window clears. ## 5. SAFETY-34: the latch is not the alarm `persistent_notification` is **in memory**. Home Assistant restarts and the card is gone while the fault runs on — which is precisely how the 2026-09-02 outage went unseen for **6 h 25 m with the detector correct throughout**. So the durable half and the visible half are joined, and the join is `Controller._circ_announced`: a **per-process** flag, deliberately *not* persisted. The latch in `/data/state.json` says *"this site is tripped"*; the flag says *"this process has put that in front of a human"*. A restart clears the flag and keeps the latch, so **the notification is re-raised on the first cycle after every start** — which is the first cycle after a Home Assistant restart, because the add-on restarts with it. **One code path serves both** the fresh trip and the restart, on purpose: two paths would be two chances for the restart one to rot unnoticed, and the restart one is the case nobody exercises by hand. Mutations **M13** (flag initialised from the latch) and **M18** (the call removed) both take it red. ## 6. Mutation ledger Every run on a **freshly copied tree with no `__pycache__`, mounted `:ro`** into the CI image — the structural immunity MUTATION.md records for CI and for SAFETY-25 — so no stale `.pyc` could exist to be read. Byte deltas recorded; **three are `+0 B`, the risky delta, and are marked**. | # | file | mutation | Δ | result | |---|---|---|---|---| | M1 | `circulation.py` | `sum(abs(v))` → `sum(v)` in the sensor | −5 B | **RED** — the 6000 W, 2000 W and three-unit checks | | M2 | `circulation.py` | N≤1 returns `None` instead of `0.0` | +1 B | **RED** — AC 5's nine-reading sweep | | M3 | `circulation.py` | a missing reading at N≥2 returns `0.0` | −1 B | **RED** — "health from an absence" | | M4 | `circulation.py` | drop `max(0.0, ...)` | — | **EQUIVALENT, not run as a claim.** For a same-sign roster the two sums accumulate the same magnitudes in the same order and are bit-identical; 700 000 random rosters produced no negative. Argued at the line and in the check's own text. | | M5 | `circulation.py` | threshold `<=` → `<` | −1 B | **RED** — "exactly 700 W forever does not trip" | | M6 | `circulation.py` | window `<` → `<=` | +1 B | **RED** — "trips at 75 s, not before" | | M7 | `circulation.py` | the window removed entirely | −85 B | **RED** — both slew-transient checks | | M8 | `circulation.py` | `None` no longer clears the window | +34 B | **RED** — the stale-reading gap check | | M9 | `circulation.py` | the latch removed | −123 B | **RED** — "restored as tripped stays tripped" | | **M10** | `main.py` | **the sensor derived from `self.allocation.shares`** | +60 B | **RED** — AC 2's headline check. This is the card. | | M11 | `main.py` | the `circulation` claim never filed | −235 B | **RED** — `test_watchdog.py` **and** `test_peakguard.py` 10f/10g | | M12 | `main.py` | the latch not persisted to the store | −112 B | **RED** — all three durability checks | | M13 | `main.py` | `_circ_announced` initialised from the latch | +21 B | **RED** — SAFETY-34's re-raise | | M14 | `main.py` | the operator clear leaves `_circ_announced` set | −45 B | **RED** — "the next trip would raise nothing" | | M15 | `arbiter.py` | `circulation` scoped `SCOPE_UNIT` | **+0 B** | **RED** — `test_arbiter.py` ×3 and `test_peakguard.py` ×3 | | M16 | `config.yaml` | schema floor `400` → `100` | **+0 B** | **RED** — the measured-knee check | | M17 | `circulation.py` | default `700` → `500` | **+0 B** | **RED** — the CFG-03 pin and the not-a-round-number check | | M18 | `main.py` | `await self.check_circulating()` removed | −39 B | **RED** — all four notification checks | | M19 | `main.py` | publish `round(x or 0.0)` instead of `None` | −68 B | **survivor on the first battery — GAP CLOSED**, then RED | **M19 is recorded as a survivor because it was one.** The first battery found no check grading what `publish()` does when a per-unit reading is missing, so turning *"I do not know"* into *"0 W"* on the one surface an operator actually watches went unnoticed — the sensor's own `None` rule, defeated one layer out. A check was added and the mutation re-run; it is red now. The run that found it was purged, so it is a result and not an artefact. ## 7. What this card does NOT close * **Inverter B's ramp and lag are placeholders.** Every transient number in §3 was produced with inverter A's parameters copied onto B (`measured=False`). SPIKE-04 measures the real ones and is the revisit trigger for the 1.75× margin. **Do not present any figure here as a measurement of inverter B.** * **A wedged inverter still cannot be stopped by this add-on.** §1 says so; the notification says so; there is no software fix and this card does not pretend to one. * **A loop below ~350 W per unit is not reported.** Deliberate, §3. * **The saturation freeze fires under a wedged unit and leaves a standing grid error.** Observed on the rig while producing §2's numbers: with B wedged, the loop's anti-windup test compares a site target against a measured site power that cannot track it, freezes the integrator and leaves the meter parked at −3750 W. Nothing alarms on that today — a freeze is an ordinary control action by design. It is a real finding, it is **not** in scope here, and it wants a card of its own.