TARIFF-18: price_taxes_eur_kwh stops shipping at half the real figure

`price_taxes_eur_kwh` shipped at 0.06 EUR/kWh with no recorded provenance -
no card, no date, no component list - and roughly HALF the true Flemish
all-in non-energy figure. It now ships at 0.11736, and the rows it is made
of are in the code rather than in this message:

  Fluvius distribution (Antwerpen)              5,35   c EUR/kWh
  Bijzondere accijns, "Alle verbruik"           4,876
  Bijdrage groene stroom en WKK Vlaanderen      1,51
  Energiebijdrage (0 EUR/MWh since 2026-08-01)  0
                                               ------
                                               11,736 c EUR/kWh = 0.11736

Eneco residential card for Flanders, September 2026, incl. 6 % VAT.
`app/price.py`'s FLEMISH_TAXES_COMPONENTS_EUR_KWH carries the rows and
test_price.py section 1b re-adds them - and also compares the total against
the card's own figures typed in the test file, so an edit that moved the
rows and the default together is still caught.

WHAT THIS IS NOT. It is not an arbitrage-correctness fix and it cannot be.
This scalar is a LEVEL component: an additive constant cancels exactly in
`max - min` and leaves the argmin where it was. TARIFF-17 shipped that proof
and it is unchanged - test_price.py 16b drives six flat scalars spanning and
exceeding the whole per-DSO range and gets the identical cheapest hour and
the identical spread to the last digit. DOCS and the CHANGELOG say so in
those words.

WHAT IT IS. A display and guard fix:

  * every number an operator reads, which at half the true value made the
    add-on look considerably better than it is; and
  * §17's negative-price guard in arbitrage.py - the one rung that tests an
    ABSOLUTE all-in price rather than a difference. It fires when
    `spot < -(markup + taxes)`, so its boundary moves -0.09 -> -0.14736
    EUR/kWh of spot. test_arbitrage.py section 2c drives both sides through
    the shipped decide() and pins the boundary from below as well.

The default is Antwerpen's real row, near the LOW end of the 0.117-0.131
per-DSO band, and that is deliberate: the error directions are not
symmetric. Too high carries a genuinely negative hour above zero and the
add-on exports into paid-for disposal - §17's own case. Too low only
declines a discharge that would have paid.

TARIFF-17's INTERACTION, WHICH HAD TO BE DECIDED. Nothing in that rung
hardcoded 0.06; it read PRICE_OPTION_DEFAULTS, so moving the default moves
what it refuses. The Supervisor sets `App.options = deepmerge(config.yaml
defaults, stored options)`, so a saved blob carries the key whether it was
typed or not - every stored 0.06 became "non-default" with nobody editing
anything, and a working Walloon or Brussels site with a taxes table would
have met SystemExit(78) on the upgrade over an inert number. price.py now
carries SUPERSEDED_TAXES_DEFAULTS_EUR_KWH = (0.06,) and validate.py reads a
superseded default as untouched too. The rung is NOT weakened: 0.1198 beside
a table is still refused by name, and the refusal now names both figures.

config.yaml and PRICE_OPTION_DEFAULTS moved together; CFG-03's tripwire
(test_price.py section 1, test_defaults_pin.py) stayed green by agreeing.
test_price.py section 0's fourth check was REWRITTEN rather than re-pointed:
it used to justify the file's own grading constants by observing that the
shipped pair was degenerate (0.06 is exactly twice 0.03). TARIFF-18 ends
that coincidence, so the sentence is no longer true and is not kept.

29/29 test files green. Mutation ledger on the PR.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

goodwe_controller/app/custom_formula.py

@@ -520,13 +520,16 @@ def implausible_all_in(spec: FormulaSpec, taxes_eur_kwh: float):
 
     ⚠️ THE LOW END IS GRADED ON THE ENERGY COMPONENT AND THE HIGH END ON THE
     ALL-IN FIGURE, AND THAT ASYMMETRY IS THE CHECK RATHER THAN AN OVERSIGHT.
-    `price_taxes_eur_kwh` ships at 0.06, which is three times the low bound -
-    so a card read a HUNDRED times too small comes out at 0.0016 EUR/kWh of
-    energy, is carried over the floor by the flat tax addend alone, and passes
-    a band applied to the all-in total. The hundredfold error is precisely
-    what this exists to catch, so the floor is applied where it can still see
-    it. The ceiling is applied to the all-in figure because that is the number
-    the site is really billed at, and taxes only push it up.
+    `price_taxes_eur_kwh` ships at 0.11736 (TARIFF-18; it was 0.06 before, and
+    the argument was already decisive at that figure), which is nearly SIX
+    times the low bound - so a card read a HUNDRED times too small comes out at
+    0.0016 EUR/kWh of energy, is carried over the floor by the flat tax addend
+    alone, and passes a band applied to the all-in total. The hundredfold error
+    is precisely what this exists to catch, so the floor is applied where it
+    can still see it. ⚠️ Raising the default made this trap WIDER, not
+    narrower: the addend that does the carrying got bigger. The ceiling is
+    applied to the all-in figure because that is the number the site is really
+    billed at, and taxes only push it up.
 
     ⚠️ AND THE LIMIT, WITH THE CLAIM. This grades the CARD'S OWN POINT - one
     price, at the monthly index the card assumed - and not every hour of every

goodwe_controller/app/price.py

@@ -818,6 +818,69 @@ def plan_is_provisional(read: PriceRead) -> bool:
 # Options: what a plugin may see, and what it may not
 # --------------------------------------------------------------------------- #
 
+# --------------------------------------------------------------------------- #
+# TARIFF-18: what `price_taxes_eur_kwh` IS MADE OF
+# --------------------------------------------------------------------------- #
+
+# ⚠️ THE DEFECT THIS TABLE PREVENTS IS THE ONE THE SHIPPED 0.06 WAS: A NUMBER
+# NOBODY COULD SOURCE. 0.06 EUR/kWh is roughly HALF the real Flemish non-energy
+# figure, and because no reader could see what it was made of there was nothing
+# to argue with. Every row below is one line of the Eneco residential card for
+# Flanders, September 2026, INCLUDING 6 % VAT, converted from the c EUR/kWh the
+# card prints to the EUR/kWh this option takes. `price_taxes_eur_kwh`'s default
+# is their sum, and test_price.py section 1b re-adds them and refuses a default
+# that is not exactly that.
+#
+# ⚠️ THIS IS A PER-DSO FIGURE, AND IT IS THE DISTRIBUTION ROW THAT MOVES. Across
+# the eight Fluvius DSOs that row runs 5,28 c EUR/kWh (Midden-Vlaanderen) to
+# 6,70 (West), so the all-in Flemish total runs about 0.117 to 0.131 EUR/kWh.
+# A site outside Antwerpen should type its own total; the other two rows are
+# Flanders-wide and do not move with the DSO.
+#
+# ⚠️ AND THE DEFAULT SITS NEAR THE LOW END OF THAT BAND ON PURPOSE, BECAUSE THE
+# TWO ERROR DIRECTIONS ARE NOT SYMMETRIC. This scalar is a LEVEL component: it
+# cancels exactly in `max - min` and cannot move which hour is cheapest
+# (test_price.py 16b measures that as a family). The one DECISION it reaches is
+# §17's negative-price guard in arbitrage.py, which tests the ABSOLUTE all-in
+# price of the sell hour. A figure set too HIGH carries a genuinely negative
+# hour up above zero, and the add-on exports into paid-for disposal - the exact
+# case §17 exists to refuse. A figure set too LOW only declines a trade that
+# would have paid. So where a default must stand in for eight different DSOs,
+# it belongs at the bottom of the band and not in the middle of it.
+#
+# ⚠️ `energiebijdrage` IS ZERO, AND IT IS A ROW HERE RATHER THAN AN ABSENCE.
+# "Vanaf 1 augustus 2026 bedraagt de energiebijdrage 0 EUR/MWh" - it was merged
+# into the bijzondere accijns. Anyone re-deriving this total from a guide
+# written before that date will find a separate energiebijdrage line and add it
+# on top of an accijns that already contains it. The zero row is here so that
+# the double-count is visible as a decision rather than as an omission.
+FLEMISH_TAXES_COMPONENTS_EUR_KWH = (
+    ("Fluvius distribution, Antwerpen", 0.0535),
+    ("Bijzondere accijns, 'Alle verbruik' - no volume bands", 0.04876),
+    ("Bijdrage groene stroom en WKK Vlaanderen", 0.0151),
+    ("Energiebijdrage - 0 EUR/MWh since 2026-08-01, inside the accijns", 0.0),
+)
+
+# ⚠️ TARIFF-18, AND IT IS NOT HOUSEKEEPING - IT DECIDES WHICH CONFIGS START.
+# TARIFF-17's rung in validate.py refuses a site that sets `price_taxes_profile`
+# AND leaves `price_taxes_eur_kwh` at something other than the shipped default,
+# because the table wins and the scalar would decide nothing. It compares
+# against the DEFAULT rather than against presence, because the Supervisor sets
+# `App.options = deepmerge(config.yaml defaults, stored options)` and a saved
+# blob therefore carries every schema key whether the operator typed it or not
+# (measured: the reference install's export is 70 of 71 keys - CHANGELOG 0.9.0,
+# `tools/supervisor_selfapi_probe.py` §D).
+#
+# So moving the default turns a previously ACCEPTED configuration into
+# `SystemExit(78)`. A site that stored 0.06 - which is every install that has
+# ever saved its configuration - and that also carries a taxes table would stop
+# starting on the upgrade, over a number it never typed and that decides
+# nothing. That refusal would be TRUE and USELESS: the rung's subject is a
+# number the OPERATOR typed, and a superseded shipped default is not one. It
+# still reads as "untouched" here, and the rung's sentence names both figures.
+SUPERSEDED_TAXES_DEFAULTS_EUR_KWH = (0.06,)     # TARIFF-02 .. TARIFF-17
+
+
 # ⚠️ CFG-03, AND HOW THIS TICKET AVOIDS WIDENING IT. Option defaults in this
 # add-on already live in three places - config.yaml, main.py's `o.get(k, X)`
 # fallbacks, and a dataclass default - held apart only by a tripwire in
@@ -836,7 +899,9 @@ def plan_is_provisional(read: PriceRead) -> bool:
 PRICE_OPTION_DEFAULTS = {
     "price_provider": "off",
     "price_markup_eur_kwh": 0.03,      # §14 tariffs.energy_price.markup_eur_kwh
-    "price_taxes_eur_kwh": 0.06,       # §14 tariffs.energy_price.taxes_eur_kwh
+    # TARIFF-18: the sum of FLEMISH_TAXES_COMPONENTS_EUR_KWH above, to the
+    # card's own last digit. §14 tariffs.energy_price.taxes_eur_kwh.
+    "price_taxes_eur_kwh": 0.11736,
     "export_price_eur_kwh": 0.04,      # §14 tariffs.export_price_eur_kwh (AC4)
     "price_csv_path": "/share/goodwe_prices.csv",
     "price_feed_url": "",

goodwe_controller/app/validate.py

@@ -330,7 +330,9 @@ from .inverter import roster_entries
 from .maintenance import MAINT_OPTION_DEFAULTS
 from .p1 import is_enabled, validate_meter_options
 from .peakguard import PEAK_OPTION_DEFAULTS
-from .price import PRICE_OPTION_DEFAULTS, PROVIDERS, RETIRED_PROVIDERS
+from .price import (
+    PRICE_OPTION_DEFAULTS, PROVIDERS, RETIRED_PROVIDERS,
+    SUPERSEDED_TAXES_DEFAULTS_EUR_KWH)
 from .static_tariff import (
     ProfileInvalid, TAXES_PROFILE_OPTION, parse_static_profile,
     parse_taxes_profile)
@@ -1444,13 +1446,32 @@ def _price_problems(opts: dict) -> list[str]:
         # the price-entity/static_profile pair above. The table decides when it
         # is set, so a non-default scalar left beside it is a number the
         # operator typed that changes nothing, on the quantity §11.4 makes
-        # hardest to notice. It is compared against the SHIPPED DEFAULT rather
+        # hardest to notice. It is compared against the SHIPPED DEFAULTS rather
         # than against presence, because the Supervisor writes every schema key
-        # into the options file whether the operator touched it or not.
+        # into the options file whether the operator touched it or not - so
+        # "the operator did not type this" has to be read off the VALUE.
+        #
+        # ⚠️ TARIFF-18: "UNTOUCHED" IS A SET, NOT ONE NUMBER, AND THE DEFECT
+        # THAT MAKES IT ONE IS AN UPGRADE THAT STOPS A BATTERY CONTROLLER
+        # STARTING. The Supervisor sets `App.options = deepmerge(config.yaml
+        # defaults, stored options)`, so a saved blob carries every schema key
+        # whether the operator typed it or not - the reference install's export
+        # is 70 of 71. When TARIFF-18 moved this default 0.06 -> 0.11736, every
+        # such blob went from "equal to the shipped default" to "not equal to
+        # it" without anybody editing anything, and a site that also carries a
+        # taxes table would have met `SystemExit(78)` on the upgrade. The
+        # sentence below is about a number the OPERATOR TYPED; a superseded
+        # shipped default is not one, so it still reads as untouched. The set
+        # is in price.py beside the default it supersedes, because the two only
+        # ever move together.
         scalar = _number(opts, "price_taxes_eur_kwh",
                          PRICE_OPTION_DEFAULTS["price_taxes_eur_kwh"])
         shipped = PRICE_OPTION_DEFAULTS["price_taxes_eur_kwh"]
-        if scalar is not None and abs(scalar - shipped) > 1e-12:
+        untouched = (shipped,) + tuple(SUPERSEDED_TAXES_DEFAULTS_EUR_KWH)
+        superseded = ", ".join(
+            str(u) for u in SUPERSEDED_TAXES_DEFAULTS_EUR_KWH)
+        if scalar is not None \
+                and not any(abs(scalar - u) <= 1e-12 for u in untouched):
             problems.append(
                 f"{TAXES_PROFILE_OPTION} is set AND price_taxes_eur_kwh is "
                 f"{scalar} rather than its shipped {shipped}. THE TABLE WINS: "
@@ -1458,7 +1479,10 @@ def _price_problems(opts: dict) -> list[str]:
                 f"the scalar, so the number you typed there would decide "
                 f"nothing and nothing would say so. Set price_taxes_eur_kwh "
                 f"back to {shipped}, or clear {TAXES_PROFILE_OPTION} to keep "
-                f"the flat figure.")
+                f"the flat figure. (A scalar still sitting on a SUPERSEDED "
+                f"default - {superseded} - is accepted and NOT refused: "
+                f"that is a number this add-on wrote into your options "
+                f"blob, not one you typed.)")
 
         # ⚠️ THE UNITS RUNG, AND IT IS A SECOND QUANTITY RATHER THAN A
         # RESTATEMENT. Every Belgian DSO prints these bands in c EUR/kWh