TARIFF-03: static day/night and fully-fixed tariffs, first-class

§9.2 puts a large share of the Belgian installed base on a static profile, and
an EMS that only works under dynamic pricing is an EMS for a minority. A new
`static_profile` option describes a two-period day/night tariff - or a single
fixed price - and app/static_tariff.py turns it into the same canonical
{start, eur_per_kwh, provisional} series the fetched providers emit.

Not a sixth provider plugin, for two mechanical reasons. capabilities() is a
classmethod, so a plugin's PriceProduct is fixed when the class is written -
but §9.2 makes STATIC and FIXED two different products and which one a site is
on is a property of the operator's data; StaticProfile.product derives it from
the number of distinct prices. And the plugin framework exists to stop a
FETCHED figure being marked up twice, which a number typed as all-in cannot be.
So the profile sits where §11.4 already says it does - under the providers, as
the fallback. Configured product and feed-is-down are one generator differing
in one flag, so the degradation path cannot rot unused.

"No arbitrage" is a type. TariffPlan.arbitrage() returns a variant whose
ALLOWED arm carries the spread and the cheapest/dearest hours and whose REFUSED
arm carries a reason and nothing else - .spread_eur_kwh on a refusal raises
rather than answering 0.0, so an optimiser cannot compute a trade from one.
Four refusals, all derived: peak guard holding, no price data, plan
provisional, or the series is FLAT. The last is AC2: a fixed tariff disables
arbitrage by arithmetic, not by matching on an enum. peak_guard_active is a
required keyword argument, so §10.1's priority 2 over 3 cannot be skipped.

Time-window shifting reaches the one shiftable load that exists: main.py's
cheap-window flag falls back to the static profile, and the UI gained a Tariff
row. Cheap is STRICTLY below the seven-day mean - `<=` would call every hour of
a flat tariff cheap, and 48 h taken on a Friday is two-thirds weekend.

A profile must tile every day type exactly once, checked at startup; a gap is
refused with the range named rather than filled in. `22:00-07:00 mon-fri` does
not cover Saturday morning, and that trap is what the check catches.

validate.py rule 7's stated reason expired exactly as TARIFF-02 predicted: the
test_price.py section 12 tripwire went red naming static_tariff.py. The message
now says what is true instead, and the tripwire is re-aimed rather than removed
- consumer set pinned, expired phrase asserted gone. Rule 7 also grew a second
refusal for static_profile alongside the HA price pair, the same silent-loser
conflict and a live one.

CFG-03 is not widened: static_profile went into price.py's PRICE_OPTION_DEFAULTS
- the one in-code mirror pinned to config.yaml by a check - and the new module
carries no defaults dict of its own.

Measured on the two committed days of this house's real P1 meter. 2026-08-20
(Thursday): 15.220 kWh imported, 9.606 day / 5.614 night, EUR 4.7185 under
day/night vs EUR 4.6725 flat, shifting saves EUR 0.8069 = 9.606 kWh x the
0.0840 spread, derived twice. 2026-08-23 (Sunday): 0.728 kWh, all of it
night-priced, which is the weekend row proving itself. §17 names six Belgian
scenarios; this is the seventh, and it is two days rather than a season - the
file says so rather than implying an annual figure.

All 12 suites green. Eleven mutations of static_tariff.py were each caught by
at least one check.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015VXjA3LWccN1rJsk3okyPC

goodwe_controller/app/main.py

@@ -45,6 +45,7 @@ from .hass import HomeAssistant
 from .maintenance import IDLE, MaintConfig, Maintenance
 from .mqtt import MqttPublisher
 from .p1 import P1Ingest, build_source, is_enabled
+from .static_tariff import static_status
 from .tariff import PeakStore, PeakTracker
 from .validate import ConfigRefused, refuse, validate_startup_config
 from .watchdog import SignWatchdog, SignWatchdogConfig, loop_is_following
@@ -208,6 +209,10 @@ class Controller:
         self.grid = self.soc = self.batt = None
         self.peak_fc = None
         self.cheap = False
+        # TARIFF-03. One line of prose for the status page saying WHICH tariff
+        # window we are in and why it is or is not cheap - so "Cheap window:
+        # no" is an evidenced answer rather than a bare no.
+        self.tariff_words = "no static profile"
         self.last_write = None
         self.last_write_at = None
         self.last_write_ok = None
@@ -261,9 +266,31 @@ class Controller:
             now_p = await self.hass.number(now_e)
             avg_p = await self.hass.number(avg_e)
             self.cheap = (now_p is not None and avg_p is not None and now_p <= avg_p)
+            self.tariff_words = "Home Assistant price entities"
         else:
-            # Fixed-tariff site: never force a paid grid top-up, wait for sun.
-            self.cheap = False
+            # TARIFF-03. §9.2 makes a static day/night tariff a first-class
+            # product, and its required EMS handling is TIME-WINDOW SHIFTING.
+            # The add-on has exactly one shiftable load in 0.5.x - the
+            # maintenance cycle's cheap-window grid top-up, ~15 lines below in
+            # cycle() - so this is where the window reaches something that moves
+            # energy. With `static_profile` empty this returns False and the
+            # behaviour is bit-for-bit what it has always been: "fixed-tariff
+            # site, never force a paid grid top-up, wait for sun".
+            #
+            # ⚠️ SYNCHRONOUS AND I/O-FREE, ON PURPOSE. The provider-backed
+            # resolver (static_tariff.resolve_tariff) can perform an HTTP fetch,
+            # and this coroutine is on the path that feeds the ESP32 heartbeat -
+            # a supplier's TLS timeout here would be a supplier able to push the
+            # add-on towards layer 1's 30 s veto. Generation from a static
+            # profile is pure arithmetic, so §2.3's "regenerate on the tick"
+            # applies and there is nothing to block on. Putting a fetched series
+            # on this path needs a BACKGROUND refresh and belongs with OPT-04.
+            #
+            # ⚠️ AND IT CANNOT BE BOTH. validate.py refuses static_profile
+            # alongside the two Home Assistant entities, because this `if` picks
+            # one and the loser is silent.
+            self.cheap, self.tariff_words = static_status(
+                o, datetime.now(timezone.utc))
 
         if self.inputs_ok:
             if self.inputs_bad_since is not None:
@@ -998,6 +1025,7 @@ class Controller:
             ("Maintenance phase", self.maint.phase),
             ("Maintenance due", "now" if next_due is None else next_due.strftime("%Y-%m-%d")),
             ("Cheap window", "yes" if self.cheap else "no"),
+            ("Tariff", self.tariff_words),
         ]
         return {
             "banner": banner, "level": level, "rows": rows, "checks": checks,