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.

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.

⚠️ AND FCST-05 WALKED INTO IT AGAIN, IN ITS OWN NEW CHECK, WHICH IS WHY THE RULE IS “mutate every check you add”. price_history.py reports a malformed point row from two places into one field: _usable_days() records what it FOUND when the file was opened, and _remember() records what it DROPPED on the next refresh. Both land in last_error, and words prints last_error. The first draft of the new check asked "malformed point row" in words — which whichever rung is still standing satisfies — so deleting _remember()'s note entirely was a −1 B SURVIVOR of the whole suite, on the half of the fix that tells an operator the cache self-healed. It is graded on the TENSE now (… in <day> at open, … dropped from <day> after the refresh), the two are asserted to DIFFER, and the paired mutation — both notes deleted, −91 B — is red on 15 named checks. Same shape as TEST-16 and the same fix: grade the reason, not the verdict, and when two rungs answer one stimulus, mutate them together.

⚠️ AND FCST-06 FOUND THE COUNT ITSELF LYING — LOW, NOT SILENT. A mutation whose red is a traceback does not report one red; it reports however many checks ran before the traceback, and grades none of the ones after it. The new section drove M4 (self._days = before → self._days = {}) and the run printed 1 FAIL. The true figure is 3: an f-string in the next check read len(read.points), and .points on a no_data raises Absence by design, so the harness died mid-section with the remaining checks ungraded. That is why()'s and derived()'s rule — "it answered nothing" and "it broke on the way to answering" must not grade the same — arriving in the printed operand of a check rather than in its condition, which is the half that is easy to miss because it looks like formatting. Two things follow:

• a mutation report's red COUNT is only a lower bound until the run is seen to have reached the end of its section. Read the output, not the count;
• the total accessor has to cover what a check PRINTS, not only what it asserts. test_price_history.py 5d added npts() beside why() for exactly this, and re-driving M4 against it moved 1 FAIL to 3.

Worse, had the traceback landed one check earlier the mutation would have produced no named red at all — a result that reads like a broken harness and gets retried rather than read.

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. TWELVE 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 THE ELEVENTH IS IN A MEASURING INSTRUMENT RATHER THAN IN A CHECK, which is where the seventh was too. SAFETY-38 round 4's render probe - the thing that decides whether a mutation changed the SENTENCE and not merely the bytes - numbered each interpolated operand BY ORDER OF APPEARANCE. After a transposition the other operand takes the same number, so all thirteen mutant renders came back BYTE-IDENTICAL to the clean tree: the probe compared the swap against itself, and its output read exactly like "the edit is inert". Keying the value to the operand's NAME fixed it. Habit 16.

⚠️ 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.

• ⚠️ ARCH-02's OWN REHEARSAL HARNESS, CAUGHT BY ITS OWN MUTATION BATTERY — the THIRTEENTH instance, and the third in an INSTRUMENT rather than in a check. tools/rehearse_roster.py reports orphaned Home Assistant entities by composing the ids the add-on announces before the roster switch and after it, and diffing. Both sides are composed by the same build. So the two mutations that change the id composition itself — renaming the MQTT device ("GoodWe" -> "GoodWe Controller"), renaming one site sensor ("Grid power" -> "Grid power W") — moved every id on both sides equally, and the harness reported "no orphans" about a change that orphans the entire live entity list. It read exactly like a clean transition. The first draft's M5/M6 came back exit 0 and exit 2, and neither was the failure they name.

  The fix is habit 2 with a filename: the reference has to be data that does not move with the code. --live-entities takes a list of the ids the install actually has, tools/rehearsal/live-entities-recorded.txt is the recorded stand-in that keeps it live in CI, and a build that announces an id the list does not carry is now a COMPOSITION DRIFT finding rather than a silence. ⚠️ The anchor moved for the same reason: it had been compose(mqtt.DEVICE["name"], p1["name"]) == "sensor.goodwe_p1_sample_age", which any renaming of the device satisfies by moving both operands, and it is now composed from two recorded literals.

  Ask of an instrument what habit 4 asks of a check: where did each side of this comparison come from — and if a mutation of the subject moves both sides, the instrument is decoration.

  ⚠️ AND REVIEW FOUND TWO MORE IN THE SAME CARD, ONE OF THEM INSIDE THE FIX FOR THE OTHER — the FOURTEENTH and FIFTEENTH. Both are the pin, not the tool, and both are the same sentence in a new costume: a check whose data cannot reach the failure it names.

  • Fourteenth — a COUNT cannot tell one red leg from two. The rehearsal reports two independent routes to the disarmed latch (SAME-STEP and STAGED) and prints every finding twice per red leg: once in that leg's own block and once in the closing summary. The check named "NOT THE SAME-STEP PATH ALONE" was written `out.count("LATCH CAME UP DISARMED")

    = 2, so **one** red leg always satisfied it. Measured on three builds: shipped code (both legs red) → 4; migrate_unit_keys()handed the roster name (SAME-STEP fixed) → 2, **passes**; a guard-side fix (both fixed) → 0. The check reportedok` on the build whose only remaining failure is the path it says is not the only one. The fix is to parse the legs and require the finding in each, which is habit 2 again: grade the thing, not a total over the thing.

  • Fifteenth — and it is INSIDE THAT FIX, which is the third time this file has had to write that sentence. The first leg-splitter opened on a LEG <id> marker and never closed, so every line after the last marker was attributed to that leg — including the closing summary, which repeats every finding from every leg. The last leg therefore read red whenever any leg was red, and the new per-leg check was the old count with extra steps. It was caught by building the one fixture that separates them: a tree in which SAME-STEP is genuinely clean and STAGED is not. The tool now prints END LEG <id> and the splitter closes on it.

    The rule that falls out, and it is the cheap one: a per-thing check that has never seen the things DISAGREE is a total. Part 5b exists to make them disagree on every run.

    ⚠️ AND ONE THAT HAS ONLY SEEN THEM DISAGREE IN ONE ARRANGEMENT IS A TOTAL OVER THAT ARRANGEMENT. Review found this by attacking the fix itself. Part 5b does make the legs disagree, on every run - and was still blind to a build that merely REORDERS them, because it had only ever seen the clean leg printed LAST. Three edits, two of them ordinary refactors (reorder the report legs, reword a summary line), produced all checks passed from a splitter that closed ZERO legs.

    A fixture cannot enumerate the arrangements, so the STRUCTURE is asserted instead: a leg may not open while one is open, and every leg that opens must be explicitly closed. That fires on the FIRST edit of all three attacks, whatever the order or the wording. When a fixture cannot enumerate the arrangements, assert the invariant they share.

• 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.

• ⚠️ SAFETY-47 IS THE TWELFTH, AND IT IS THE SECOND INSIDE A COMMITTED EVIDENCE ARTIFACT. DECISIONS/SAFETY-10-shadow-mode.md §6 tabulated a live run and a shadow run agreeing on arb_power_w, on the reason verbatim and on the arbiter's winner, and concluded that shadow mode reaches the same decision. Two independent reasons it could not have gone red, and closing either one alone closes nothing:

  • its fixture is peak_cap_w: 15000 against a 350 W house, so the capacity guard never engages and the thing whose invariance is being claimed — SAFETY-45's sizing of the buy leg from the billed-quarter meter — is in the run and inert. ⚠️ The harness's own comment says so: "at this scenario's peak_cap_w: 15000 it is not binding anyway". The rule was written down beside the check it disabled and nobody read it as a disclosure;
  • and every identity row reads _sa[0]/_la[0] — the first charging sample. At elapsed = 0 the projection is the held level, so the two runs agree to the float even at a cap that does bind. Measured: widening the fixture alone — the obvious fix — leaves that comparison passing.

  ⚠️ THE SECOND REASON IS A NEW SHAPE FOR THIS LIST: AN INDEX, NOT A FIXTURE. Ask of every identity claim not only "could this data differ" but "at the point I sampled it, could it differ yet". A comparison taken at t = 0 between two runs that diverge because one of them acts is a comparison of a plant with itself, and no amount of widening the fixture changes that. The replacement, test_arbitrage.py part 3d, grades the whole run — 716 of 720 charging cycles differ — and grades the [0] agreement as an expectation, so nobody rebuilds a check on it believing it covers something.

  ⚠️ AND THE FIX'S OWN FIRST DRAFT CARRIED A THIRTEENTH. The new part's action-log check could not reach the log line at all: the sentence was an f-string inside Controller._shadow_settle(), and the only suite that drives that method uses a meter_source: off fixture where no arbitrage decision — and therefore no caveat — exists. Deleting the caveat from it left all 29 files green. It is shadow.log_line() now. A sentence assembled at a call site is a sentence no check can grade, which is CFG-04's substring lesson arriving from the other direction.

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 SINK IS HALF THE SCOPE, WHICH IS HOW THE FIRST THREE ROUNDS OF THIS SCAN MISSED THE PLACE THE CODEBASE ACTUALLY KEEPS ITS SENTENCES. The scan classified a sentence as operator-facing when it was appended, assigned to a reason-shaped name, or logged — and every one of its 16 reported members was one of those. None was RETURNED. A method formatting its own attributes and handing the string back — ClampResult.describe(), PeakDecision.explain(), every reason-builder in the tree — was outside all of it, and so were sentences handed to a constructor as reason= or placed under a "text" dict key. Four zero-byte survivors of a green 21-file suite were sitting there, two of them on the alarm SAFETY-40 and SAFETY-41 are about. The general form: an enumeration is scoped by a SINK as much as by a PREDICATE, and a sink list is a hand-written list like any other (habit 12). Ask of any such scan: which syntactic forms does this call a message, and what does the code under it actually use?

16. ⚠️ AN INSTRUMENT THAT ASSERTS A COMPLETENESS IT DOES NOT HAVE IS WORSE THAN NO INSTRUMENT, AND ITS BLIND-SPOT LIST IS PART OF THE CODE UNDER REVIEW. tools/symmetric_message_scan.py printed five honest gaps and a census count, and a reader — including its author, twice — took the count for the family. The gap that mattered, the RETURN sink, was in none of the five. A gap list is not a disclaimer; it is a claim, and it is the claim most likely to be believed because nothing else in the output argues with it. Two consequences:

    • State what is NOT scanned, largest hole first, as a list of forms — not "this under-reports". The tool now names %s-style lazy logging (_LOG.error("… %s … %s", a, b), where the operands are arguments, so no f-string census can ever see them), .format()/%/+/.join() sentences, sentences that leave through a dict or dataclass, yield, message attributes outside its own constant set, and everything outside app/. Where the list is derived from a constant in the file, it is printed from that constant, so the two cannot drift.
    • AND THE PROBE THAT GRADES THE MUTATIONS IS SUBJECT TO EVERY HABIT ABOVE. Round 4's render probe gave each interpolated operand a value by order of appearance — so after a transposition the other operand took the same number and all thirteen mutant renders came back byte-identical, which reads exactly like the edit changed nothing. Keying the value to the operand's NAME fixed it. That is habit 4, in the measuring instrument: the fixture's own values were arranged so the failure it was built to see could not change the answer. Eleventh instance of habit 4 in this file, and the second one in an instrument rather than in a check.

17. ⚠️ TWO TERMS OF A CONJUNCTION THAT MOVE TOGETHER IN EVERY FIXTURE ARE ONE TERM AS FAR AS THE CHECKS ARE CONCERNED - TWELFTH INSTANCE OF HABIT 4, and the third found by an author's own battery rather than by review. SAFETY-37's freshness gate is unchanged >= 35 s AND |standing| >= 250 W AND |travel| >= 250 W. Deleting the MIDDLE term left every check in the first draft green, because in all of them a command that had travelled 250 W had also ended up above 250 W: the fixture never separated the two, so one of them was decoration as far as the suite could tell. The case that separates them is a site being brought to REST - the register reaches its new value on the same read at which the OLD command is still standing, so the travel term alone reads 1300 W of unfollowed command while the site sits truthfully at +5 W. Ask of every conjunction: is there a fixture in which each term is the ONLY one that is false? If not, the suite cannot tell an AND from an OR.

18. ⚠️ AN UNVERIFIED REVERT IS THE SAME DEFECT AS STALE BYTECODE, AND TWO HARNESSES SHARING ONE BACKUP PATH IS THE WORST VERSION OF IT. SAFETY-37's sweep hit this twice, in ascending order of nastiness.

    • A mutation's container run overran a two-minute command budget and the wrapper was killed between the edit and the cp that puts the file back, leaving app/freshness.py mutated on disk. Nothing announced it; the next mutation's harness cheerfully fingerprinted and graded the mutant plus a second mutation.
    • Then two copies of the sweep were started - a scheduling mistake, not a tool defect - and the harness kept its backup at the FIXED path /tmp/mut.bak. One copy saved app/main.py there; the other restored it over app/freshness.py. The result was a 238 KB freshness.py that still parsed as Python, plus main.py left holding a live mutation. No error, no warning, and the only reason it was noticed is that the tree fingerprint did not match the recorded clean one.

    Two rules, and the first is the cheap one:

    • Fingerprint after the revert, not only before the run. tools/mutation_run.sh prints the tree it is about to grade for exactly this reason; the revert deserves the same treatment, and a mismatch is a stop-everything result rather than a note.
    • A harness's scratch file must be unique per invocation (mktemp), so that two of it cannot silently overwrite each other's work. A fixed path in a tool that edits source is a shared mutable global with a filename.

19. ⚠️ A FIXTURE IN A SHAPE NOBODY PUBLISHES GRADES THE PARSER AGAINST THE PARSER — FOURTEENTH INSTANCE OF HABIT 4, AND THE FIRST WHERE THE FIXTURE AND THE CODE UNDER TEST SHARED A SHAPE RATHER THAN A NUMBER. TARIFF-08. price.py's _points_from_json() read doc["data"] as a list of {start, price_eur_mwh} objects. api.energy-charts.info publishes parallel unix_seconds / price arrays and has no data key at all, so generic_dayahead raised SourceUnavailable on every live fetch it ever made — and the suite was green, because all three price suites built their bodies with json.dumps({"data": [...]}). The fixture was derived from the parser's guess, so no mutation of the parser and no amount of coverage inside that loop could ever have reached the failure. §11.4 then turned it into a correct silent degradation: parse error -> no_data -> static profile -> arbitrage off, with nothing naming the cause.

    Habit 2 with a network on the end of it: the reference has to be data the code under test did not shape. For a parser that means BYTES, captured from the source and committed unmodified, with the URL, the retrieval time and a checksum beside them - scenarios/energy-charts-be-price-*.json and its -captures.json provenance, re-derived by the replay so an edited fixture stops being a capture. Two granularities, because the same endpoint answers hourly before 2025-10-01 and quarter-hourly after it and a fixture at one spacing cannot grade an assumption about the other.

    ⚠️ AND THE SURVIVING SYNTHETIC FIXTURES ARE NAMED FOR WHAT THEY ARE. Three shipped plugins point at endpoints nobody has verified (TARIFF-07), so no capture exists for them; their fixture builder is called synthetic_row_feed at every call site, because the next reader's default assumption will otherwise be that a green check means the feed parses.

    ⚠️ ONE OF THIS CARD'S OWN NEW LINES WAS DECORATION AND THE BATTERY SAID SO. The columnar parser first rendered its instants with brussels() before returning them. assemble() already renders every plugin's points, so removing the parser's call changed nothing observable - M4 came back a survivor on a :ro, purged tree, which is not the direction stale bytecode fabricates. The line was removed rather than fenced with a check: a second copy of a rule that already has an owner is indistinguishable from a no-op, and the mutation that proves the rendering is real belongs on assemble(), where it is now aimed.

20. ⚠️ A FIXTURE GRADES THE RESPONSE. NOTHING ABOUT THE REQUEST IS REACHABLE FROM ONE, AND THE TRANSPORT HAD BEEN RECORDING IT ALL ALONG. TARIFF-09, and it is habit 19's closed loop with the other half still shut. generic_dayahead.fetch() took since and until and asked for the bare ?bzn=BE, which answers ONE Brussels day - so §8.3 dropped every hour past today from the trade set as provisional and the optimiser never saw tomorrow as firm, at any hour of any day. Measured at 09:00: 15 firm hours and 33 carried of 48, both ends of the permitted cycle inside one calendar day; at 23:00, 1 and 47, with the firm spread no longer clearing the round-trip cost.

    TARIFF-08 had just fixed the RESPONSE side of this same plugin by committing real bytes. It could not have caught this: a captured body is the answer to a URL, and no property of any body says which URL was asked for. canned() in test_price.py had recorded (url, timeout_s) on every call since TARIFF-02 and not one check had ever asserted on the first element - so the harness knew the plugin was ignoring its arguments and nothing asked it. The fix is one line of habit: where a plugin takes arguments that shape a request, assert on the REQUEST off the injected transport, not only on what comes back. Section 2c does, and the shipped-defect mutation (restore the bare URL, -173 B) is red on six named checks in test_price.py and two in test_price_history.py.

    ⚠️ AND A MUTATION THAT TURNS A READ INTO no_data CRASHES A SUITE INSTEAD OF NAMING A CHECK, UNLESS THE CHECK EXPECTS IT. _NoData.points raises Absence by design, so derived(...) < derived(...) over two absent reads is a TypeError and [p for p in plan.read.points] is a traceback - habit 5's shape with an exception in place of a hang. The mutation that matters here is the "defensive" one somebody writes after reading this card: refuse when the feed returned fewer days than we asked for. It is exactly what a healthy feed does every morning before the ~13:00-14:00 CET auction, and switching arbitrage off for it would be a worse defect than the one being fixed. It is red BY NAME in test_price.py (33 checks, the AC's own line among them) and takes test_price_history.py down at FCST-04's section 1, whose _before read is unguarded - a red, but an unnamed one. That is recorded rather than retrofitted: guarding another card's section is a change to what its checks report, and it belongs to whoever next touches it.

21. ⚠️ A CHECK CAN BE GREEN UNDER ITS OWN CARD'S NAMED MUTATION, AND TWICE IN ONE FILE THE REASON WAS THAT THE WRONG QUANTITY EVENTUALLY REACHES THE RIGHT VALUE. TEL-10's acceptance was "a run that winds the integrator into the bound must show the published number reaching the bound", and its named mutation was "publish prev_w instead of i_w". The check was GREEN on the mutant: the command reaches the same bound too, twelve cycles later, and a check that only reads the VALUE cannot tell the two apart. The same file's "a stopped controller publishes not-running" was green under deleting that branch's assignments outright (−45 B and −67 B), because the fixture STARTED stopped and __init__ writes the same values. Both are habit 4 - the data could not reach the failure - and both were found by the card's own battery. The fixes are the shape to copy:

    • where two quantities CONVERGE, grade the order or the interval, not the value: "the integrator reaches the bound BEFORE the command does", and a PLATEAU (the lead sits at exactly −800 W for eight consecutive cycles) rather than a maximum, because a maximum is one tick and a plateau is the shape;
    • where a branch WRITES a value the constructor also writes, the fixture has to pass THROUGH the other state first. Stop the controller part-way through a run that has already wound the integrator to −5000 W, so a row left standing is a WRONG row and not merely an unset one.

22. ⚠️ AN EXPLANATION IN A COMMENT IS A CLAIM, AND SAFETY-48 SHIPPED TWO THAT WERE INVENTED. A gate was written one-sided (if target > slewed: min(...) elif target < slewed: max(...)) under a comment saying the two-sided band max(lo, min(hi, i_w)) was a BUG that would drag a trailing integrator toward the command, with a worked example. It is not a bug and the example was wrong: target is monotone in i_w, so the other clamp cannot reach, and the two spellings agree on 205 920 of 205 920 swept states. A second bullet said two placements of the same cap "differ on 118 of 256 252 ticks"; that 118 had been measured against a different pair and the placement actually being compared is bit-identical on the shipped configuration - 0 of 256 246 ticks. Both sentences were plausible, both were load-bearing for a design choice, and neither had been run. The rule: a comment that says "X would be wrong" is subject to the same battery as a check - BUILD X AND MEASURE IT. Where the answer is "equivalent", say so with the sweep size and keep the spelling for what it NAMES; where the answer is a number, quote the run it came from. An invented justification for a correct decision is still a defect, and it is the kind a reviewer cannot see because the code is right.

23. ⚠️ THE MUTATION IS SUBJECT TO EVERY HABIT ABOVE, HABIT 4 INCLUDED - AND THE PURGE, THE FINGERPRINT AND THE BYTE DELTA ALL SAY IT TOOK. SAFETY-57's battery reported a survivor at +21 B for a mutation of Freshness._open_window(): self.graded_from = float(now_mono) rewritten as float(self.changed_mono or now_mono), which is meant to re-anchor the verdict's window to the register's own history and so delete the card's whole exit. The harness purged, the tree fingerprint showed the edit on disk, the delta was non-zero, and the mutant really did run. It was still a survivor for a reason that has nothing to do with the property: in the fixture the register never moves after t = 0, so changed_mono is 0.0 - and 0.0 or x is x. The mutant was a no-op on that stimulus. Rewritten with an explicit is None test (+82 B) it is red on four named checks.

    Stale bytecode is a mutation that never ran. This is a mutation that ran and could not change the answer on the data it was given, which is habit 4 exactly, one level up - and none of the three things a mutation report is required to state (MUTATION.md's own list) can see it, because all three are about the file rather than about the stimulus. Two rules:

    • Ask of every survivor what it would have had to change, and check that the fixture reaches that value. Here: "does any fixture have a non-zero changed_mono at the moment _open_window() is called?" The answer was no, and it is one line to ask.
    • Prefer a mutation that CANNOT be a no-op. or, and, truthiness on a numeric, a default argument and a getattr fallback all have a value at which the mutant and the shipped tree coincide. An explicit comparison, a constant swap or a deleted statement does not.

    ⚠️ Note where this one was found: in the battery of a card whose whole subject is a check that cannot reach the failure it names. Second instance in an instrument rather than in a check since habit 16, and the third overall.

    ⚠️ AND THE SAME CARD'S BATTERY CAUGHT A HABIT-22 COMMENT IN THE FIX ITSELF, WHICH IS WHY THESE TWO BELONG NEXT TO EACH OTHER. freshness.py shipped ⚠️ RELEASE BEFORE GRADE, AND THE ORDER IS LOAD-BEARING with a worked reason. Swapping the two calls is zero bytes and survived the battery: _grade() acts only when |standing| >= move_w and _release() only when |standing| < move_w, so at most one can act on any read and the order is not observable. Habit 22 says build X and measure it; the battery is what builds X. The comment now states the disjointness and the suite pins that - at 0, 100, 249, 250, 251 and 1300 W - rather than an order nothing depends on.

    ⚠️ SECOND INSTANCE, TEL-11, AND THE NO-OP WAS A SATURATED RAIL RATHER THAN A VALUE. The card's whole subject is that a PV reading must never reach the control law, so its central mutation is self.grid = self.grid - self.pv_w in read_inputs() - +106 B, on disk, purged, genuinely running - and it came back a SURVIVOR of a six-file battery. The property held in no sense: the fixture drove a 6 kW export over 12 cycles, which puts the loop against its rail, and a command moving slew_w every cycle produces the SAME ramp for -6000 W and for -14000 W of apparent error. The mutant ran and could not change the answer. Two things generalise past PV:

    • A SATURATED ACTUATOR IS A VALUE AT WHICH EVERY INPUT COINCIDES. The habit-23 list above names or, and, truthiness, default arguments and getattr fallbacks - all expressions with a coinciding value. A rail, a clamp, a slew limit, a deadband and a latched alarm are the same hazard in the plant: they are where a controller's output stops being a function of its input. A fixture that parks there cannot separate any two inputs, and this repository's control fixtures park there by default, because the dramatic stimulus is the saturating one.
    • SO THE PRECONDITION IS NOT "DOES IT COMMAND SOMETHING", IT IS "DOES IT REST SOMEWHERE THE MUTATION COULD MOVE IT FROM". test_pv.py part 6 now drives a 600 W import the loop SETTLES on, asserts the resting target is well inside the rail, and asks habit 23's own question as a check: shift the METER by the same 8 kW and confirm the commands really would have moved. On the first fixture that question answers NO, in one line, and it is the line that turns the identity into evidence.

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.

TARIFF-15 — the card-graded formula, mutation by mutation

Twenty-two mutations, one per check the card added, run rather than reasoned about. Harness: /home/homelab/.cache/t15-mut/run.py, backups beside it rather than in a shared scratchpad — two agents' harnesses collided in one this week. Each run restores from backup, purges __pycache__ on the host first, and grades through the CI image with the tree bind-mounted :ro, so the interpreter cannot write a cache into the tree under test at all (TEST-15's structural immunity, borrowed).

No survivors. Two entries are +0 B and are called out as such, per the reporting rule.

	mutation	file	Δ	red
M1	CARD_TOLERANCE widened to 100 — the self-check stops checking	custom_formula.py	+1 B	8
M2	CARD_TOLERANCE tightened to 0 — the other direction, so the tolerance is a number and not a shape	custom_formula.py	−1 B	16
M3	units becomes optional	custom_formula.py	+10 B	1
M4	the factor == 0 rung removed	custom_formula.py	−8 B	1
M5	the factor < 0 rung removed	custom_formula.py	−7 B	1
M6	the vat_pct band widened to ±1000	custom_formula.py	+6 B	2
M7	the non-finite rung removed from _finite()	custom_formula.py	−26 B	2
M8	the non-numeric rung removed from _finite()	custom_formula.py	−16 B	4
M9	an unknown top-level field ignored instead of refused	custom_formula.py	−2 B	1
M10	the plausibility floor applied to the all-in figure instead of the energy one	custom_formula.py	+0 B	2
M11	hourly stops averaging and emits the feed's own points	custom_formula.py	+12 B	3
M12	the hourly bucket takes the FIRST quarter instead of the mean	custom_formula.py	−11 B	1
M13	the preview drops the index column from each row	custom_formula.py	−13 B	1
M14	the preview is emitted on every refresh rather than once	price.py	−8 B	1
M15	custom_formula declares ALL_IN — the double-counting lie	price.py	−41 B	10
M16	a stale card never warns	custom_formula.py	−8 B	1
M17	a stale card REFUSES instead of warning	validate.py	−3 B	1
M18	the empty-formula refusal removed from the startup gate	validate.py	−38 B	1
M19	the index scaled to EUR/kWh before the formula — the factor-1000	price.py	+2 B	7
M20	an eval call planted in app/custom_formula.py	custom_formula.py	+14 B	1
M21	custom_formula stops passing the caller's range to the feed	price.py	+0 B	1
M22	PAIRED: M1 and the plausibility band removed, together	custom_formula.py	−60 B	12

The four that are worth reading rather than counting

M13 was a SURVIVOR of the whole suite on the first attempt, at −13 B. The check read "index EUR/MWh -> all-in EUR/kWh" in log — which is the preview's heading. Deleting the index column from every row left the heading saying it prints something it no longer printed, and nothing went red. That is this file's third failure mode arriving in the check written to close it: the assertion ran, the sentence was true, and the data could not reach the failure it named. It is graded on a rendered ROW now, built here from the captured document (' 216.080 -> 0.30123'), and M13 is red.

M10 is +0 B and it is a real defect, not a synthetic one. It came out of writing the mutation rather than out of review: implausible_all_in()'s floor was applied to the all-in figure, and price_taxes_eur_kwh shipped at 0.06 — three times the 0.02 floor — so a card read a hundred times too small (0.0016 EUR/kWh of energy) is carried over the floor by the flat tax addend alone and passes. The hundredfold error is exactly what that band exists for. The floor is applied to the energy figure now and the ceiling to the all-in one, both directions are graded, and the trap is stated as a check in its own right so the asymmetry cannot be "tidied up" later. (Annotated 2026-09-13: TARIFF-18 raised that default to 0.11736, nearly six times the floor. The addend that does the carrying got BIGGER, so the trap is wider than when M10 was measured and the asymmetry is more load-bearing rather than less.)

M15 is the one the framework CANNOT catch, and the reds say which half does. Declaring ALL_IN makes assemble() add nothing, and section 3's all-in check is derived from the declaration — so it passes on the lie, exactly as price.py's trap 1 says no code can catch a misdeclaration. What goes red is the docstring/declaration agreement check, the card reproductions, and the sources pin: ten reds, none of them from the arithmetic. That is the guarantee at its true size — the two claims are held to agree, and whether either is true about somebody else's tariff remains human.

M22 is the paired run (TEST-16). The card self-check and the plausibility band both answer a unit error, so each could be masking the other. Weakened together they produce twelve reds rather than the eight M1 alone produces, and the band's own checks stay red — so neither rung is doing the other's work.

What this battery does NOT establish

It does not establish that a card is the right card. Every mutation above moves the relationship between the coefficients and the printed price; none of them can move the relationship between the printed price and the operator's actual contract, because nothing in this repository observes that. A consistent-but-wrong pair passes every one of these checks, by construction, and DECISIONS/TARIFF-15-the-card-is-the-grader.md §3 says so in the same sentence as the claim.

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 -rfs 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-09 11 mutations over app/price.py and the two-day capture, all red, no survivors	not at risk	direction, and method: every mutation was applied to a FRESH cp -a of the clean worktree rather than reverted, so there is no revert to verify (habit 18) and no shared scratch path two runs could collide on. Each ran through tools/mutation_run.sh, which purges and fingerprints. Byte deltas recorded on the PR; one is +0 B - a single price digit edited inside the committed capture, the risky delta - and the re-derived sha256 catches 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.