goodwe-addon/goodwe_controller/MUTATION.md

# Mutation runs in this repository — and the one way they lie

Nearly every safety claim in this add-on was established the same way: change
the shipped module, run the suites, watch one go **red**, put the module back,
watch it go **green**. There is no coverage tool here and there is not meant to
be — the check that matters is whether a *check* notices when the behaviour it
names is removed.

That method has exactly one silent failure mode, and TEST-15 exists because we
walked into it.

## The defect

FCST-03's developer reverted `self.provisional` to `here.provisional`, re-ran,
and reported the mutation as a **survivor**. It was not. CPython decides a
cached `.pyc` is still valid from two numbers:

* the source file's **size in bytes**, and
* the source file's **mtime truncated to whole seconds**.

`self` and `here` are the same length, and the revert happened in the same
second as the edit. Neither number moved, so the interpreter loaded the
bytecode it already had. Confirmed at the time by disassembly: **the source read
`here`, the running code loaded `self`.** The suite had graded code that was not
there — no error, no warning, exit status 0.

The same collision, in the other direction, can leave a **red** standing on
correct source after a revert that never took.

### Which way it lies, and why that scopes everything

A mutation that never took effect leaves the suite **green**, and a green run of
a mutated tree is reported as a survivor. So stale bytecode **manufactures
survivors**; it cannot manufacture a red. The false-red case exists but
announces itself, because a developer chases a failure they cannot explain.

Two consequences, and both are used below:

* a recorded **"all red, no survivors"** result is not at risk from this defect;
* a recorded **survivor** — and a recorded *zero*, such as a coverage-audit
  count of 0 — is exactly what this defect produces.

`test_control.py`'s coverage-audit table says the same thing in its own terms:
the error is one-directional, so every figure there is a lower bound at worst.

## The rule

**Purge `__pycache__` before every mutation run.** Not afterwards, not usually,
not when the edit looks big enough.

```sh
cd goodwe_controller
tools/mutation_run.sh                     # every test_*.py in this directory
tools/mutation_run.sh . test_tariff.py    # or just the ones you are watching
tools/mutation_run.sh "$GOODWE_ADDON_REPO/goodwe_controller"   # from elsewhere
```

The harness purges, prints a `sha256`/byte-count fingerprint of every `app/*.py`
it is about to grade, runs each suite under `python3 -B`, and fails if a cache
appeared during the run. Diff two fingerprints and the file you mutated is the
line that changed — which is also how a mutation report proves *which source*
produced it.

### What does **not** fix this

| | writes bytecode | reads a stale `.pyc` |
|---|---|---|
| `python3 -B` | no | **yes** |
| `PYTHONDONTWRITEBYTECODE=1` | no | **yes** |
| purging `__pycache__` | (unchanged) | **no — nothing to read** |

Both flags are *write-side only*. A mutation run always has a cache already,
because the previous run wrote it, so a harness that only adds `-B` closes
nothing. This is measured, not read off documentation: `test_bytecode.py`
part 2 arranges the collision and shows both flags still running the old code.

`-B` is still worth passing — it stops **this** run leaving a cache for the
**next** edit to inherit, which is the one nobody is thinking about three
mutations into a batch. Purge for this run, `-B` for the next one.

### And not a `sleep`

One-second mtime resolution is the *mechanism*, not the enemy. Waiting out the
clock would slow every run down, and would still only cover the edit somebody
remembered to slow down. Stop trusting mtime instead.

## Reporting a mutation

State the things a reviewer cannot reconstruct afterwards:

1. **the byte delta** of the mutated file (`+5 B`, `+0 B`). `+0 B` is the risky
   one — say so;
2. **that the mutated line was on disk** when the run started (the harness
   fingerprint, or a `grep` of the line);
3. **which suite went red, and on which named check** — "the suite is red" and
   "the check that watches this is red" are different claims;
4. for a **survivor**, that the run was purged. An unpurged survivor is not a
   result.

## The other thing a mutation sweep cannot see: masking (TEST-16)

Stale bytecode is not the only way a survivor lies. **Two guards can mask each
other**, and a sweep that mutates one line at a time is structurally blind to it.

TEST-16 is the worked example. `static_tariff.arbitrage()` refuses a
one-firm-hour series at `len(firm) < 2`, and refuses a flat series at
`spread == 0.0`. A single firm hour *also* has a spread of zero. So:

* weaken the firm-pair rung alone → the flat rung refuses the stimulus anyway;
* weaken the flat rung alone → the tiny-spread stimulus is still refused, just
  for the wrong reason;
* and the suite, grading `kind == "refused"`, reports **nothing either way**.

Both rungs could then be weakened *together* and still nothing would report —
which is precisely the state in which the next edit to either one opens a real
hole. It survived four rounds of review on TARIFF-03 and FCST-03.

Two rules come out of it, and both are cheap:

1. **Grade the reason, not just the verdict.** "Refused" and "refused for the
   right reason" are different claims, and a masked rung is the case where the
   first is true and the second is false. A refusal sentence is what the
   operator reads; it is also the only observable that moves when one rung
   quietly absorbs another's work.
2. **When two rungs can answer the same stimulus, mutate them together.** One
   extra run per suspected pair. If a sweep finds two survivors in the same
   function, that pair is the first thing to try — TEST-16's two survivors were
   adjacent lines in one function and neither was individually live.

## The third way a check lies: its DATA cannot reach the failure it names

Stale bytecode manufactures survivors from a mutation that never ran. Masking
manufactures them from a second guard doing the first one's work. This one
manufactures them from a **fixture**: the check runs, the assertion is
evaluated, the sentence above it is true — and the numbers it compares are
arranged so that the failure it describes could not have changed the answer.

It is not hypothetical and it is not rare. TEN instances in two weeks; four
were found by review, two - CFG-04's fixture pair - by an author's own mutation
battery, which is the cheaper place, one by review again, in the one
place nobody had thought to point the rule at: not a check in the suite, but a
COMMITTED EVIDENCE ARTIFACT four documents cite - the eighth INSIDE THE FIX
WRITTEN TO CLOSE THE SEVENTH, the ninth inside the SITE HALF of the card
that names the rule in its own text - and the TENTH INSIDE THE FIX WRITTEN TO
CLOSE THE NINTH, for the second time in this list. See SAFETY-38 below: the
check that closed it asserted a NUMBER and not the number's POSITION.

⚠️ **AND IT HAS NOW APPEARED IN SIX CONSECUTIVE CARDS.** The seventh instance,
MAINT-05's, is the one that says why: the defect is not carelessness about
fixtures, it is that **a check and the thing it checks were built from the same
constant**. Ask of every difference-claim not "is this assertion true" but
"where did each side of this comparison come from" - and if the answer is the
same place twice, the check is decoration.

* **ARB-03** shipped a call-site scan asserting that every `claims.append` in
  `cycle()` routes through `actuator_of()`. Its own parse **saw 3 of the 8
  appends**; the other five were invisible to it and would have passed however
  they were routed.
* **ALLOC-01** shipped a replay generator to hunt for envelope escapes. It found
  **0**. A widened generator over the same allocator found **39,991**.
* **DEV-02** shipped `"each unit's supervised bound is ITS OWN max_w — give
  inverter B a different rating and the claim filed on inverter B moves with
  it"`, comparing inverter B's bound against `_b2.max_w`. The fixture defaulted
  B's rating to A's, so it compared `(-5000, 5000)` against `(-5000, 5000)` —
  **a number against itself**. Filing both per-unit bounds from
  `self.inverters[0]` left **all 19 files green**.
* **CFG-04** wrote *"an entry that omits `soc_entity` has NO SoC sensor and does
  not borrow the flat one"* against a fixture whose **flat `soc_entity` was
  blank**. Inherited and not-inherited were both `""`, so the mutation that
  makes `build_roster()` fall back to the flat key survived. The fixture now
  sets a real entity there, and the check asserts that the flat value is present
  as well as that the entry's is empty.
* **CFG-04** also wrote *"main.py runs the per-unit range check
  UNCONDITIONALLY"* as a **substring test over `app/main.py`'s source**. The
  mutation that defeats it puts the call back inside `if entity:` — one level of
  indentation — and the substring is still there. That is habit 4 below in a new
  costume: the check asserted against the TEXT of the thing under test rather
  than against its behaviour. It now drives the shipped `run_control()` on a
  two-inverter config, **under a deadline**, because the mutation's real symptom
  is that the controller enters its loop and never returns.
* **MAINT-05** shipped `Controller.__init__` calling
  `migrate_maint_keys(store, self.inverters[0].name, ...)` under a comment
  saying *"it targets `self.inverters[0].name` and NOT `UNIT_A` ... writing
  `UNIT_A` here would deposit an install's whole maintenance history under a
  name that is not on the roster at all"*. `inverter.UNIT_A` **is** the string
  `"inverter-a"`, and every two-pack fixture in `test_maintenance.py` named its
  first roster entry `inverter-a` — so the two expressions were the same value
  in every check that existed, and swapping them left **all 19 files green**
  while losing a real install's whole maintenance history. Two-pack fixtures are
  now `["garage", "shed"]`, each behind a precondition check (habit 1) that the
  first name is not `UNIT_A`.

  ⚠️ **AND THE POSTCONDITION HAD THE SAME SHAPE AS THE FIXTURE.**
  `store._verify_moves()` read back the keys it had just written, under the
  namespace it had just been handed — so it verified clean, and the caller
  stamped the schema marker, on a migration nothing would ever read. *A check
  that reads back the namespace it was handed cannot detect being handed the
  wrong one*: it compared a thing against itself, exactly as DEV-02's fixture
  compared `(-5000, 5000)` against `(-5000, 5000)`. The habit-2 fix is the same
  one — grade against something the thing under test did not supply, here the
  ROSTER the machines read.

  ⚠️ **AND THE FIX ITSELF CARRIED THE DEFECT, WHICH IS THE SIXTH CARD IN A ROW
  AND THE FIRST TIME IT HAS APPEARED *INSIDE* A REMEDY.** The fix round's
  recovery check was `migrate_maint_keys(_m5, ROSTER[0], ROSTER)` — the
  **corrected** name. It measures recovery along the one path where the operator
  has *already fixed the bug*, and nothing in the 19 files called
  `migrate_maint_keys()` twice with the **same wrong** `unit`. So the refusal
  the card was rejected twice to obtain lasted **exactly one start**: measured
  at Controller level over one persisted store, roster `["garage", "shed"]` —
  construction 1 `ok=False misdirected=4 moved=4 kept=0 marker=<absent>`,
  construction 2 `ok=True misdirected=0 moved=0 kept=4 marker=1`. On start 2
  rule 1 routes the wrongly-written keys to `rep.kept`, `rep.moved` is empty,
  the roster loop iterates over nothing, and the marker is stamped on a
  migration that reached no readable key — after which the early return skips it
  forever, *including after the call site is fixed*. The check was true and
  passed for the wrong reason. Habit **9** below is what falls out of it.

* **CFG-04's `tools/supervisor_shape_probe.py` §B** — and this one is the rule
  reaching outside the suite. The probe is the committed evidence that
  `config.yaml`'s `inverters: []` default is load-bearing, and four documents
  quoted it as answering *"Missing option 'inverters' in root"*. §B validated
  the reconstructed LIVE options blob, which is missing many required keys
  unrelated to this card, so its refusal named whichever of THOSE the validator
  reached first — `meter_freeze_s`, `p1_phase_export_entities` and
  `sign_disagree_w` on three different runs. The quoted string was never
  produced by the instrument. And the assertion was a bare **`not ok`**: delete
  `inverters: []` from `config.yaml` and §B went on printing **PASS**, blind to
  the exact regression it was cited for. §B is now an isolated counterfactual —
  the shipped defaults, and the same defaults minus that one key — asserting on
  the **key name in the refusal**; the mis-cited blob survives, relabelled, as
  §B2. Re-run with the default deleted it prints `2 CASE(S) FAILED` and exits 1.

  ⚠️ **A committed transcript is a check, and it decays like one.** Nothing in
  this document had been pointed at `tools/`, because the artifacts there are
  filed as *measurements* rather than as *checks* — and a measurement whose
  assertion cannot fail is exactly the thing this section is about. Two habits
  follow, and both are habit 5 and 6 below.

* **SAFETY-38** — `main.py`'s
  `site_standing = float(sum(standing.values()))`, the first argument of
  SAFETY-30's latching site sign detector *and* SAFETY-18's `looks_frozen()`
  input. `test_watchdog.py`'s `_sign_site` is the suite's **only** N≥2 site
  fixture, and it runs shares of about **−2500 W each** — every one
  individually over the 320 W gate it is configured with. On numbers like those
  `sum`, the mean and `max(key=abs)` **all agree**, so the reduction could be
  swapped for either of the other two and the site guard went **blind with the
  whole suite green** — still commanding −500 W of charge into a +2500 W import at
  t = 595 s with `following=True`. At a roster of **one** it is worse and it is
  not a fixture defect at all: `sum == mean == max == the one share`
  *identically*, so every such mutation is genuinely **equivalent** there and no
  N=1 fixture could ever separate them. The fixture that separates them is the
  one the detector exists for — **per-unit shares EACH BELOW the gate whose SUM
  clears it** — and it is now `test_watchdog.py` part 9, at asymmetric ratings
  so that all four candidate reductions give four **distinct** answers.

  ⚠️ **AND THE CARD'S OWN SEARCH FOR ITS NEXT SURVIVOR FOUND ONE, WHICH IS THE
  POINT OF ASKING.** Having built the fixture, the question *what mutation would
  this NOT see?* produced `float(self.target)` — the arbiter's site target
  instead of the sum of what stands on the wire — at **−11 B**, green across the
  whole suite, because every fixture in the repository was built where the two
  are the same number. They separate only when a device's reported range is
  narrower than its `max_w`, since the `device` claim is filed **per actuator**
  and never bounds the site target. Closed in the same commit, by a
  counterfactual that asks for −500 W while −250 W stands.

  ⚠️ **AND THEN THE FIX ITSELF WAS THE TENTH INSTANCE — A SUBSTRING WHERE THE
  FAILURE WAS POSITIONAL.** The check written to pin the banner asserted
  `f"{sum(...):.0f} W" in reason`: that **"−500 W" appears somewhere** in the
  sentence. Swapping the detector's first two arguments
  (`evaluate(site_standing, self.grid, …)` → `evaluate(self.grid, site_standing, …)`)
  is a **ZERO-BYTE** edit that leaves both numbers in the string and moves each
  into the other's slot — so the substring is still found, **in the meter
  slot**, and the whole suite stayed green while the latching site-stopping
  banner told the operator which instrument read what **exactly backwards**.
  The fix is to assert the **ORDERED PAIR**,
  `f"commanded {sum:+.0f} W against a meter reading {grid:+.0f} W"`.

  ⚠️ **AND THE ELEVENTH WAS THE SAME DEFECT ONE CALL SITE OVER — THE ONE A
  SHIPPED INSTALL CAN ACTUALLY SEE.** Round 2 pinned the operand order of
  `SignWatchdog.evaluate()` at `main.py:1620`. That call site is the **site**
  detector, and `test_watchdog.py` part 9c asserts it is **never armed at a
  roster of one** — which is every install this add-on has. The **per-unit**
  call at `main.py:1560` was left unpinned, and swapping its first two
  arguments is the same **ZERO-BYTE** edit: `disagrees()` is symmetric in them
  (`commanded_w * against_w < 0` with an `abs()` gate on both), so **no trip
  decision can change** and the full 21-file suite stays green — measured. What
  moves is five banner lines, including the one persisted to `sign_reason` and
  re-read after a restart: *"commanded −1000 W against its own measured power
  +1000 W"*, operands inverted, on the only sign-disagreement sentence a
  one-inverter install can ever print. Closed in round 3 by the ordered pair on
  **both** per-unit banners — the N≥2 `its own measured power` one and the N=1
  `a meter reading` one — red on four named checks, green in the other twenty
  files. **Habit 15 is what falls out of finding the same shape twice in the
  same card.**

  The general habits are **14** and **15** below.

Note what these have in common with a masked rung: the mutation *runs*, and the
suite is *honestly* green. Nothing in a purge, a fingerprint or a disassembly
can see it, because the code under test really did behave identically on the
stimulus it was given. The defect is upstream of the assertion, in what the
check was handed.

**The rule, and it is one line:**

> **Any check asserting "X differs from Y" must be run once with X and Y
> actually made different.**

Cheap habits fall out of it, and all of them are now used in this repository:

1. **Write the PRECONDITION as its own check.** `test_peakguard.py` 10g asserts
   that A and B have different ratings *before* it asserts that B's bound is
   B's. If a later edit makes them equal again, the precondition goes red rather
   than the claim going quietly vacuous.
2. **Assert against literals, not against the expression under test.**
   `== [(-_b2.max_w, _b2.max_w)]` cannot distinguish "B's number" from "the
   number this fixture happens to have twice"; `== (-3000.0, 3000.0)` beside a
   printed `A = 5000` can.
3. **Print what the check saw.** Every one of the three above would have been
   caught by a human reading one line of output — `supervised bounds by
   actuator: {'inverter-a': (-5000, 5000), 'inverter-b': (-5000, 5000)}` is
   self-evidently not evidence of a difference.

4. **Assert on the BEHAVIOUR, not on the source text of the thing under test.**
   A substring test over a module is a check on how the code is spelled;
   whitespace, an alias or a moved line defeats it while the property it names
   is gone. `test_inverter.py` part 10 has one of each — a source pin for a
   claim that genuinely IS about the code's shape, and a driven `run_control()`
   for a claim about behaviour — and the second replaced the first after the
   mutation battery walked straight through it.
5. **A check whose failure mode is a HANG needs a deadline.** Otherwise the
   mutation that defeats it produces a CI timeout with no name attached, which
   reads like flaky infrastructure and gets retried rather than read.
6. **Assert on the CONTENT of a refusal, not on the fact that one happened.**
   `not ok` is satisfied by any error at all, including one about a different
   key on a different blob. `"Missing option 'inverters' in root" in out` goes
   red the moment the refusal stops being about the thing it is cited for. This
   is habit 2 in the negative direction: a refusal, like a difference, has to be
   asserted against a literal.
7. **Vary ONE thing in a counterfactual, and vary it from an ACCEPTED
   baseline.** `supervisor_shape_probe.py` §B validates the shipped defaults
   first, precisely so the refusal on the next line has nowhere else to come
   from. Without the accepted baseline the second line is a refusal of unknown
   provenance, which is what §B used to print.
8. **A committed transcript is a check.** Anything under `tools/` that a
   document quotes is subject to every rule above, and to the mutation battery:
   break the property, re-run the instrument, and confirm the transcript goes
   red. `inverters: []` was deleted from `config.yaml` and the probe re-run
   against `ghcr.io/home-assistant/amd64-hassio-supervisor:2026.08.0` for
   exactly that reason.
9. **Exercise a refusal a SECOND time with the SAME wrong input — not the
   corrected one.** A guard that refuses once and then admits the same bad
   caller is not a guard, it is a delay, and the second call is a *different
   code path* whenever the first call left state behind. MAINT-05's roster
   grading iterated the keys it had just **written**; on the second start the
   same wrong caller found them already present, they moved to the
   `already namespaced` list, and the loop graded an empty set. Re-running with
   the **fixed** argument — which is what the check did — measures the operator's
   recovery, never the persistence of the refusal. Ask of every refusal: *what
   does this do when the caller has not been fixed and simply runs again?* And
   assert the **shape** of that second report, not only its verdict, so the
   check cannot silently revert to grading the first path.

10. **A fixture of N members cannot separate two reductions that agree on N
    members — so grade the FAMILY, and grade it from the SOURCE.** This is the
    only lesson SAFETY-32 cost four review rounds to learn, and it generalises
    past packs to every roster, list and window in this repository. Two packs
    cannot tell `max` from `min` from first from last. Three cannot tell `max`
    from `max(x[-2:])`. **The regress does not terminate in a fixture**: `[:1]`
    needs two members, `[:2]` three, `[:3]` four, and adding one more member
    moves the hole rather than closing it. Three things follow, and all three
    are now in `test_peakguard.py` parts 12c2, 12g, 12i and 12j:
    * the fixture is a **SET** — the extreme at every position of the roster,
      not one roster with the extreme somewhere;
    * the family table is **COMPUTED and PRINTED**, so a member no fixture kills
      shows up as a named survivor and takes the check red, instead of being
      absent from a list nobody re-derived;
    * where the claim is an **IDENTITY** ("this roster", "this list"), pin it
      **exactly on the AST** — `ast.unparse(arg) == "self.packs"` is false of
      every slice, where `"self.packs" in src` is true of all of them. Where the
      claim is **SEMANTIC** ("the maximum"), a shape pin would refuse honest
      refactors, so report the unreached width **with its size** instead.

11. **When a check of this shape is found, mutate its SIBLINGS before shipping
    the fix.** SAFETY-32 was rejected three times for the same defect one step
    over: the reduction, then the roster handed to it, then the reduction handed
    to the *other argument of the same call*. Enumerating the family from the
    AST and mutating each member took one afternoon and found **four more
    survivors in code the card never touched** — three of SAFETY-30's
    `any(i.sign_wd.tripped for i in self.inverters)` reductions, invisible
    because the only fixture that reached them was a roster of ONE, where
    `self.inverters[:1]` **is** `self.inverters`. Ask of every fix: *what is the
    sibling of the thing I just hardened, and does any fixture separate it from
    a slice of itself?*

12. **When the same shape has been found twice, STOP CLOSING SITES AND BUILD
    THE INSTRUMENT — and make it DISCOVER its own scope.** SAFETY-32 was
    rejected four times, and each round closed exactly the site it was handed:
    the reduction, then the roster handed to it, then the *sibling argument* of
    the same call, then the same family one *module* over, in validate.py.
    Round 4 did enumerate — and enumerated inside the `Controller` class,
    because that is where the four known sites lived. **A hand-written scope is
    the same defect as a hand-written fixture**: it is a check whose data cannot
    reach the failure it names, and it goes on passing while the thing it was
    supposed to cover sits in the file nobody added to the list. Round 5's pin
    parses every `.py` under `app/`, seeds itself from ONE option key, and
    propagates through returns, accumulator loops, attributes and *call
    arguments* to find the roster wherever it went — 183 reductions across 9
    modules. It rediscovered all four blockers without being told where to look,
    and it named two modules the hand-written list would not have contained
    (`maintenance.py`, `store.py`) while *omitting* one the list did contain
    (`watchdog.py`, which is strictly per-unit and reduces over no roster at
    all). **The list was wrong in both directions**, which is exactly what a
    computed scope is for.

13. **Say what the instrument CANNOT see, with sizes, in the same breath.** A
    structural pin grades an **identity** ("this whole roster arrives"); it can
    never grade a **meaning** (`min` vs `max` is a zero-byte edit and invisible
    to it). Ship the pin AND the behavioural set, name the gap, and give every
    unreached case its byte delta — `cycle()`'s undeliverable-unit log line
    (+4 B, still green), a subscript by a *variable* rather than a constant, a
    slice taken through an intermediate call, anything outside `app/`. **An
    enumerated list with an honest gap is worth more than a claim of
    completeness a reviewer falsifies in ten minutes**, and every round of this
    card that claimed the latter was rejected for it.

14. **An `in` test against a formatted sentence grades PRESENCE, never
    ARRANGEMENT — so assert the ORDERED PAIR.** SAFETY-38 pinned the banner of a
    latching, site-stopping alarm with
    `f"{sum(_share38):.0f} W" in ...reason` — that `"-500 W"` appears
    *somewhere*. Swapping the detector's first two arguments at the call site
    (`evaluate(site_standing, self.grid, …)` →
    `evaluate(self.grid, site_standing, …)`) is a **ZERO-BYTE** edit: both
    numbers are still in the string, each in the other's slot. The substring was
    still found — **in the meter slot** — the whole suite stayed green, and the
    banner told the operator which instrument read what **exactly backwards**.
    Whenever the property you mean is "**this** value went in **this** slot" — a
    reason string, a log line, a notification, an MQTT payload — assert the
    surrounding **literal text with the value embedded in its own position**
    (`f"commanded {x:+.0f} W against a meter reading {y:+.0f} W"`), or assert
    the fields **before** they are formatted. Two values that both appear in one
    sentence can always be transposed by an edit that costs **nothing**, and
    that no byte delta, no fingerprint and no shape pin can see. ⚠️ Note where
    this one was found: **inside the fix written to close the previous instance
    of the same family**, which is the second time in this list.

    ⚠️ **AND THE FIX FOR IT WAS ONE CALL SITE WIDE, WHICH IS THE HALF WORTH
    KEEPING.** The ordered pair went onto `main.py:1620`, the **site** detector
    — armed only at N≥2, and part 9c asserts it is **absent at a roster of
    one**. The identical swap at `main.py:1560`, the **per-unit** detector, was
    still **ZERO BYTES**, still changed no decision, still left the 21-file
    suite green — and it is the **only** sign-disagreement sentence a shipped
    one-inverter install can ever print: *"commanded −1000 W against its own
    measured power +1000 W"*, backwards, in the log, on the status page and in
    `sign_reason` after the restart the latch is designed to survive. Measured
    size: **main.py:1560, 0 bytes, 21/21 green.** So habit 14 is not "pin the
    banner", it is **"pin every call site of the banner, and say which one the
    shipped roster reaches"** — and habit 15 is how you find them all.

15. **A SYMMETRIC PREDICATE MAKES ARGUMENT ORDER A PROPERTY OF THE MESSAGE
    ALONE — so ENUMERATE THAT FAMILY BY MACHINE, and grade the CALL SITES, not
    the function.** Where a callee is symmetric in two arguments, a swap at any
    call site is invisible to every behavioural check **by construction**: not
    "no fixture happens to separate them" but *no fixture can*. There is
    nothing for a mutation battery to find, because the mutant and the shipped
    tree take identical actions on every input. The only surface that moves is
    the sentence, and the only check that can see it is one asserting the
    **ordered pair** (habit 14) at **that** call site.
    Three consequences, and all three are why this is its own habit:
    * **The unit of coverage is the CALL SITE.** SAFETY-38 pinned
      `evaluate()`'s operand order and still shipped the defect, because the
      pin was on the call two lines below the one that matters. Ask of every
      banner: *how many places call this, and which does the shipped roster
      reach?*
    * **The scope must be COMPUTED** — habit 12's argument, and SAFETY-38 is
      its proof: the family was enumerated by hand twice and was short both
      times. `tools/symmetric_message_scan.py` renames each parameter pair,
      erases every formatted string, canonicalises the commutative operators
      and iterates to a **fixpoint** over `app/` (the symmetry is usually one
      call deep — `evaluate()` is symmetric only *through* `disagrees()`), then
      classifies each sentence by where it GOES. A returned string may be a
      **key** — swapping `store.unit_key(unit, key)` renames a store key, which
      is behaviour and is MAINT-05's card — or a **sentence**, which is this
      family.
    * **Say what the instrument cannot see, with shapes** (habit 13). That scan
      under-reports semantic symmetry no canonicaliser on its finite list can
      spell; its second census, for sentences the CALLER builds, pairs only
      expressions **one leaf apart** and never sees `%s`-style logging; it
      covers only `app/`; and it **over-reports in exactly one way** — it
      erases the sentence, so a swap that would make the FORMATTING itself
      raise is scored as changing no decision. It prints all of that on every
      run. The family, every member's call sites, and which of them are pinned
      are in `DECISIONS/SAFETY-38-site-standing-pin.md` §7 — **with two
      measured, still-open survivors named there rather than rounded off**,
      both zero bytes and both 21/21 green.

And the mutation-table consequence: **a variant is not covered because a
near-miss of it is.** DEV-02's table listed the *actuator* variant of the
per-unit claim defect (`device`/`supervised` filed without `inv`), which the
static routing pin catches. The *bound* variant — right actuator, wrong
numbers — is a different defect with a different fix, and it was absent. Both
are in the table now.

## Where each surface stands

* **Local and dev-harness runs — the exposed one.** This is where FCST-03 hit
  it. `goodwe_controller/__pycache__` and `app/__pycache__` are gitignored and
  are sitting in most working trees right now. Use the harness.
* **CI — structurally immune, and it was before this card.** `.gitea/workflows/
  checks.yml` bind mounts the checkout `-v "$WS:/w:ro"`, so the interpreter
  cannot write a `__pycache__` into the tree under test at all; measured for
  TEST-15, and it fails *silently* — no error, exit status 0. Each job also
  `rm -rf`s its workspace and clones afresh, so nothing crosses between jobs on
  the shared runner. `PYTHONDONTWRITEBYTECODE=1` is now set there too, as belt
  and braces: the `:ro` is one character wide and the next person debugging a
  write will be tempted by it.
* **The shipped add-on — not affected, and this is closed.**
  `goodwe_controller/Dockerfile` has carried `PYTHONDONTWRITEBYTECODE=1` since
  it was written. There is no deploy-side finding here; do not re-open it.
* **The infra repo's `sim/` harnesses — exposed, and NOT fixed by this card.**
  `sim/replay_sign.py` and friends import the add-on out of
  `$GOODWE_ADDON_REPO` and write `__pycache__` into *both* trees
  (`goodwe/sim/__pycache__` exists today). SAFETY-02's headline validation is a
  replay, not a suite, so a mutation graded through it carries the same
  exposure. `tools/mutation_run.sh` takes the tree to purge as its first
  argument precisely so that repo can call it, but the change belongs in that
  repo and some of those harnesses want the rig. **Anyone mutating a module
  graded by a replay must purge both trees by hand until then.**

## Survey — mutation claims of 2026-08-25 … 2026-09-01

Scoped **by the property, not by re-running everything**. A claim is at risk
only if a mutation could have preserved the file's byte count *and* been
reverted inside the same second, *and* the claim is of the kind stale bytecode
can fabricate (see "which way it lies"). Sources: `git log release/1.0` and the
commit and PR bodies.

| claim | verdict | why |
|---|---|---|
| **FCST-03** M9 `self.provisional`→`here.provisional` (dd40c56, 71cd784) | **re-verified** | this is the original false survivor. Re-run with the cache cleared, M9 is caught. The shipped source was correct throughout. |
| **FCST-03** X1, X6 degenerate stimuli (71cd784) | **not at risk** | run after the purge discipline landed in that branch. |
| **SAFETY-24** 11 author + 9 reviewer mutations (e709554, 4601682) | **not at risk** | the commit records them run under `python -B` with a purged `__pycache__` and real byte deltas. Its one survivor is an equivalent mutant, argued structurally rather than by a green run. |
| **SAFETY-26** tolerance sweep over `arbitrage.py` and `static_tariff.py`, 2 survivors (2b8b8cb) | **not at risk** | purge, printed `+5 B` delta, mutated line asserted present, tree re-read before each run. One survivor is explicitly recorded at `+0 B` — the risky delta — and was produced *under* the purge. **Both survivors are now closed by TEST-16** (`test_static_tariff.py` section 9), which also found that the two of them *masked each other* — each was individually non-live only because the other rung caught its stimulus, an arrangement single-mutation testing cannot see. Its own ledger is 7 mutations, 4 of them at `+0 B`, all red. |
| **OPT-04** mutations reported on PR #22 (bdd7f18) | **not at risk** | `test_arbitrage.py`'s header records the exact command: purge, then `python3 -B`. |
| **TEST-17** `checks()` dropping `when` (504e8da) | **not at risk** | a *red* claim, and dropping an argument changes the file length. Neither half of the collision is available. |
| **SAFETY-07** wiring mutations B1/B2/B3 and `test_peakguard.py` parts 7 and 10 (2d570d8, e7c95bf) | **not at risk** | those mutations are **executed in-process**, monkeypatched onto the imported module. No source file is edited, so no `.pyc` is consulted. |
| every **"all red, no survivors"** claim in the window — TARIFF-02 (24/0), TARIFF-03 (11), MAINT-04 (10), SAFETY-18 (6+4), SAFETY-03 (6), TEL-04 (10), TEL-05 (6) | **not at risk** | direction. Stale bytecode turns a red into a green survivor, never the reverse. A red is evidence that *something* changed under the check. |
| **TEST-06**'s deleted assertion, "no new notification while parked at 0 W" (c34b5a2) | **not at risk / superseded** | it was recorded as undecidable and then *falsified* — `test_freeze.py` records the one-line mutation that takes the file red 9 times. The stronger later claim is a red one. |
| **TARIFF-01** reviewer survivor: `record_block()` ignoring its `policy` argument (0dbd485) | **re-verified — still a survivor** | re-run here through `tools/mutation_run.sh` against the 15 suites that were on the record, all green with `billed_w(block, policy)` mutated to `billed_w(block, POLICY_NET)`. The recorded diagnosis holds: every block reaching the store is single-phase, where NET, SUM and MAX collapse. **Now CLOSED by TEST-13** (`test_tariff.py` section 7), which round-trips section 7's own unbalanced `(3000, 500, -200) W` block THROUGH the store under each policy - three distinct banked figures, so a hardcoded policy takes at least two of them red. Third instance of "a stimulus evaluated where the quantity it grades is degenerate", after WITNESS-02's span normalisation and TARIFF-01's own DST window. |
| **SAFETY-25** 8 mutations against `test_peakguard.py` part 10, then 9 more after review, all red | **not at risk** | each run against a tree copied fresh with `__pycache__` excluded and mounted `:ro`, so no `.pyc` existed to go stale - the same structural immunity recorded for CI above. Byte deltas recorded on the PR; none is `+0 B`. All are **reds**, which is the direction this defect cannot fabricate. ⚠️ The second round exists because the first round's mutations were all aimed at DISARMING the guard, and the claim part 10 actually made was about the guard being FIXED - the reviewer built the fix and the suite stayed green. Bytecode was never the issue there; an unaimed battery was. |
| **SAFETY-03** reviewer survivor: `abs()` dropped from `clamp_to_rating`'s limit (6aabb83) | **re-verified — still a survivor** | re-run the same way, all 15 green. Also as recorded: unreachable under the `int(100, 5000)` schema. |
| **MAINT-05 round 3**, `migrate_maint_keys()` marker gate `if rep.ok:` → `if rep.ok or rep.kept:` (`+12 B`) | **was a survivor — now CLOSED** | measured against head `65cddf3` under the purge, tree mounted `:ro`, `19/19 PASS`. It stamps the schema marker on a migration that LOST state, defeating the older `lost` guard as well as the new `misdirected` one, because every check that reached the marker did so on a store whose `kept` list was empty. Closed by `test_maintenance.py` **9d**; the mutation is now red on three named checks. |
| **MAINT-05 round 3**, `migrate_unit_keys()` marker gate `if rep.ok:` → `if rep.ok or rep.kept:` (`+12 B`) | **found here — SAFETY-02's half, now CLOSED** | the SAME mutation one function up, on the LATCH migration rather than the history one. Measured a survivor against this branch under the purge, `:ro`, `19/19 PASS`, then closed by `test_inverter.py` part 10's new fixture — a store with `unit/inverter-a/sign_reason` already present (so `kept` is non-empty) whose `sign_tripped: true` write is dropped. Shipped: marker withheld. Mutant: marker stamped on a **disarmed latch**, and the next start skips the migration that would have re-armed it. |
| **TARIFF-01**'s other three survivors, **SAFETY-03**'s `describe()` survivor, **TARIFF-02**'s M3/M5/M7, **SAFETY-18**'s three | **still unverified** | recorded before the purge discipline, with no byte delta on the record, so a `+0 B` same-second revert cannot be excluded. All are survivors, which is the direction this defect fabricates. TARIFF-02's and SAFETY-18's were **closed by later commits whose claims are reds**, so what is unverified is the *diagnosis*, not the current state of the code. |

**Nothing here says a past result is wrong.** The two survivors re-run above
both stood. What changed is that they are now on the record as measured rather
than assumed, and the rest are labelled honestly. The still-unverified rows are
cheap to close — one harness run each — and the right moment is when somebody
next touches that module, not in a re-run campaign nobody will read.