TARIFF-08: the day-ahead feed is read in the shape it actually publishes

`generic_dayahead` could not read one byte of `api.energy-charts.info`, and
never had been able to. `_points_from_json()` asks for `doc["data"]`, a list of
`{start, price_eur_mwh}` objects; that document does not exist. Fetched live on
2026-09-10 the feed returns COLUMNAR parallel arrays and no `data` key at all -
`unix_seconds` (96 UTC epoch seconds, 900 s apart), `price` (96 floats),
`unit: 'EUR / MWh'`. Driving the shipped parser against that body:
`SourceUnavailable: the feed carried no 'data' list`. It is the only shipped
provider whose endpoint anybody has reached, so dynamic pricing did not work.

AND §11.4 MADE IT SILENT, which is why it survived to release: a parse error
becomes no_data, becomes the static profile, becomes arbitrage off - the
CORRECT degradation, saying nothing about the cause. A site would have sat on
the fallback indefinitely.

AND THE SUITE COULD NOT SEE IT, because every fixture was built from the
parser's own assumption. test_price.py, test_price_history.py and
test_static_tariff.py each built `json.dumps({"data": [...]})`, a shape invented
here and published by nobody, so the checks graded the parser against the
parser's guess - a closed loop no coverage inside it could ever have escaped.
MUTATION.md habit 19 records it as the fourteenth instance of habit 4 and the
first where the fixture and the code under test shared a SHAPE, not a number.

WHAT CHANGED

* `_points_from_columnar_json()` - a SECOND function, not a sniff. A parser that
  decides which document it received is one that can decide wrong, and a
  wrong-but-parseable response then becomes a price. Feeding the row shape to
  `generic_dayahead` is now a graded no_data.
* Unequal arrays are refused in both directions, with the two lengths in the
  reason. `zip()` stops at the shorter list silently, and a truncated `price`
  array would have produced a real series missing the evening peak - traded on
  as complete, where no data at all switches arbitrage off.
* A unit that is not EUR/MWh is refused. The plugin converts with a fixed
  0.001, and `MAX_PLAUSIBLE_EUR_KWH` only bounds prices that are too LARGE.
* `unix_seconds` are read as UTC instants explicitly; §9.3's Brussels rendering
  stays in `assemble()` rather than being copied into the plugin, where a
  mutation could not tell it from a no-op (M4 proved exactly that on a first
  draft, and the line was removed rather than fenced).
* A published null is dropped and logged with a count; an all-null body is
  no_data named by this parser rather than by the boundary validator.

FIXTURES

Two unmodified response bodies under `scenarios/`, captured by hand on
2026-09-10: quarter-hourly (2026-09-10, 96 points at 900 s) and hourly
(2025-09-10, 24 at 3600 s - the same endpoint before Belgium's 15-minute MTU).
`energy-charts-be-price-captures.json` records the URL, retrieval time, unit,
licence-as-returned and a sha256 of each, and the replay RE-DERIVES the
checksums, so a fixture edited to make a check pass stops being a capture. Data
CC BY 4.0, Bundesnetzagentur | SMARD.de, via Energy-Charts (Fraunhofer ISE),
published without changes - the same BE-zone licence check DATA-02 established.

The surviving invented fixtures are renamed `synthetic_row_feed` at every call
site. `engie_dynamic`, `totalenergies_dynamic` and `eneco_eddy` are untouched
and have no capture: their URLs are unverified and withdrawing them is
TARIFF-07's open decision. Nothing should read their green checks as evidence
that those feeds parse.

MUTATIONS - 12, all red, no survivors. Purged tree, mounted `:ro`, `python3 -B`
(TEST-15). M1 drop the equal-length refusal; M2 make it one-sided; M3 drop the
unit check; M4 `assemble()` stops rendering at the Brussels offset; M5 read
`unix_seconds` as a naive local clock; M6 zero-fill a null instead of dropping
it; M7 drop the all-null refusal; M8 sniff for the row shape; M9 drop the
deprecated warning; M10 drop the dropped-nulls warning; M11 edit one price in
the committed capture; M12 point `generic_dayahead` back at the row parser -
red across all three price suites.

END TO END, LIVE, 2026-09-10: `resolve_tariff()` returns a `TariffPlan`,
`origin='provider'`, 96 quarter-hourly points, spacing [900] s, no decimation,
first point 2026-09-10T00:00:00+02:00 at 0.30608 EUR/kWh all-in. FCST-04's H1
fix was never theoretical. All 29 test files green.

STILL OPEN: `generic_dayahead` asks for no date range, so the default URL
returns one published day - a full 48 h horizon is reached only through §8.3's
carry-forward fill.

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

goodwe_controller/MUTATION.md

@@ -673,6 +673,45 @@ Cheap habits fall out of it, and all of them are now used in this repository:
       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.
+
 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