UX-54 round 5: give blocks end at the floor point, the tab on the clock-change days

daycurve.curve() puts a point where a giving battery reaches the floor
inside a step (_floor_cut(), as it already does for a grid charge reaching
its level), so _stops() ends a give block in the quarter control stops. A
walk where control moves the packs with its own model (not the curve's
levels) matches the tab quarter by quarter in 11 cases; 25/45 % with the
peak guard: control 17:00-20:15, block 17:00-20:06.

SolarToday keys an hour by its start taken back from the UTC instant, so
the two 02:00 hours of the autumn change stay apart. test_ux54_dst.py builds
the tab (forecast_payload()) at every quarter of 27-29 March and
30 October-1 November 2027, modes on and off, in the no-tzdata zone and,
where the host has tzdata, ZoneInfo, every call under a time limit raised
as a BaseException that forecast_payload() cannot swallow.

give_later: "No block shows while a battery has no energy to give." /
"Er verschijnt geen blok zolang een batterij niets kan leveren."
DECISIONS: what the walks prove, the modes-off charge drawn on a sunny day,
the clock-change days.

No decision, command, timing or option key changes.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/DECISIONS/UX-54-forecast-tab.md

@@ -31,22 +31,28 @@ battery's expected level with its blocks. It follows the add-on, as Home does
   block where the emptiest battery is at the floor by that count, and control
   does not give there. A charge is read from the floor: a full battery covers
   the house before the cheap hour, and control charges it back then. Walked
-  every 15 minutes on a cloudy day with the house (`test_ux54.py` part 7,
-  cases A-C), control charges and gives in exactly the quarters the tab has a
-  block.
+  every 15 minutes on a cloudy day, the packs moved by control and a 400 W
+  house (`test_ux54.py` part 7, cases A-D, one price quarter per leg),
+  control charges and gives in exactly the quarters the tab has a block.
 - **A block lasts as long as control acts.** A cheap run is sized for all the
   batteries charging together, so a slower one is still below
   `modetrade.charge_to()` when it ends, and control plans the next cheap slots
   (`Controller._price_runs()`). `dayview._levels()` asks the same functions,
   `modetrade.energy()` and `priceruns.plan()`, with the packs at the curve's
   level, and draws the grid block to where control stops. Each battery's block
-  then ends where the curve has it at its own level (the curve puts a point
-  there), and a give block where it reaches the floor (a step end, within the
-  0.1 % the tab shows). Control, walked every 15 minutes through tomorrow
-  (`test_ux54.py` part 7), charges and gives in exactly the quarters the tab
-  has a block. A GIVE role counts only where control's own discharge envelope
-  (`packshare.envelope()`) is open; the walk puts each pack's cut-out at the
-  floor.
+  then ends where the curve has it at its own level, and a give block where
+  it reaches the floor: the curve puts a point at both (`daycurve.curve()`
+  cuts the step there), and the block ends at the first point where the level
+  the tab shows (0.1 %) is there. What is proven: control walked every 15
+  minutes through tomorrow with its own model of the packs, not the curve's
+  levels (`_mode_roles()` each quarter; the house from the profile, the sun
+  at 100 % trust, a GIVE role counted only where control's own discharge
+  envelope `packshare.envelope()` is open, the cut-out at the floor), charges
+  and gives in exactly the quarters the tab has a block in 11 cases
+  (`test_ux54.py` part 7, `own_walk()`), e.g. 25/45 % with the peak guard:
+  control gives 17:00-20:15, the block is 17:00-20:06. With a cut-out under
+  the floor, or a house or sun that differs from the forecast and profile,
+  control differs (Limits).
 - **The sun** is what `solarfc` reads. An hourly split (Solcast
   `detailedForecast`, Open-Meteo `wh_period`) is used as given. A daily total
   (Forecast.Solar, and any other state-only sensor, the owner's three "today
@@ -89,7 +95,7 @@ is `SolarToday.add()` after the solar read, in a `try`, in memory.
   at its level (`charge_to()`) and giving at the floor.
 - Today, a give run in the plan on a battery that is empty now has no block on
   Home (no energy to give). The tab equals Home, and says so: "The add-on plans
-  to give power. No block shows while the battery has no energy to give." The
+  to give power. No block shows while a battery has no energy to give." The
   curve gives in that run if the sun fills the battery first.
 - With no forecast for tomorrow the curve stops at the first hour of the sun,
   `solarfc.BELL_FROM_H` (06:00): `Forecast.between()` has no answer past it. The
@@ -103,11 +109,22 @@ is `SolarToday.add()` after the solar read, in a `try`, in memory.
   hour, net of the solar the house used.
 - Modes off: the count knows no sun and no house. A battery at the floor that
   the sun fills before a give gets no block until then (the tab says "The
-  add-on plans to give power. No block shows while the battery has no energy
-  to give."), and a small charge may be used by the house before the give.
+  add-on plans to give power. No block shows while a battery has no energy to
+  give."), and a small charge may be used by the house before the give. The
+  other way round, a charge is drawn even when the sun fills the batteries
+  before it: at the ceiling control then takes none (a cheap quarter at 13:00
+  on a sunny day: the tab draws the charge, control charges nothing at 95 %
+  or 100 %).
   A leg is the verdict's as it stands now, one price period, as on Home; with
   several equal prices in a row control takes the next one as each passes.
 - Measured solar starts when the add-on starts; the tab says from when.
+- Clock changes: the tab walks local hours with `dayplan._hour_slices()`,
+  which steps in UTC (SAFETY-123), and keys measured solar by the start of
+  the local hour taken back from the UTC instant, so the spring day has 23
+  hours, the autumn day 25 (two of them 02:00), and a request always returns
+  (`test_ux54_dst.py`, every quarter of both change days, with and without
+  tzdata). The solar bell is spread over hours from local midnight, so on
+  those two days it is an hour off the clock (SAFETY-123, not changed here).
 
 ## Found, not changed
 

goodwe_controller/app/daycurve.py

@@ -31,6 +31,8 @@ from .dayplan import EFF, _hour_slices, _local
 from .modetrade import CHARGE, GIVE, HOLD, HOUSE, REST
 
 EPS = 1e-9
+MIN_CUT = timedelta(seconds=1)      # no step is cut closer to its ends
+MAX_FLOOR_CUTS = 400        # a bound on the floor cuts of one curve
 GAP_S = 60.0                # a longer gap between readings is not counted
 MIN_COVER = 0.5             # share of the elapsed hour a reading must cover
 
@@ -88,10 +90,42 @@ def _spread(amount, caps, weights):
     return got, max(0.0, left)
 
 
+def _give_caps(roles, level, by, floor, hrs):
+    """`(first, rest)`: what each battery that may give can give in a step
+    of `hrs` hours (its rating, or what it holds above the floor), those in a
+    give run first."""
+    caps = {n: min(by[n].rating_kw * hrs,
+                   max(0.0, level[n] - floor) / 100.0
+                   * by[n].capacity_kwh * EFF)
+            for n, r in roles.items() if r[2]}
+    first = {n: c for n, c in caps.items() if roles[n][0] == GIVE}
+    return first, {n: c for n, c in caps.items() if n not in first}
+
+
+def _floor_cut(a, z, net, roles, level, by, floor, hrs):
+    """Where in the step `[a, z)` the first battery that gives reaches the
+    floor, or None. A shortfall is spread over a step at a steady rate and
+    shared by what each can give, so a group that holds less than its part
+    of the shortfall, one of them short of its rating, is empty at
+    `held / part` of the step."""
+    left, cut = -net, None
+    for grp in _give_caps(roles, level, by, floor, hrs):
+        held = sum(grp.values())
+        if held > EPS and left > held + EPS and any(
+                c < by[n].rating_kw * hrs * (1.0 - 1e-9)
+                for n, c in grp.items()):
+            t = a + (z - a) * (held / left)
+            if a + MIN_CUT < t < z - MIN_CUT and (cut is None or t < cut):
+                cut = t
+        left = max(0.0, left - held)
+    return cut
+
+
 def curve(batts, start, end, sun_kwh, use_kwh, *, floor_pct, ceiling_pct,
           trust=1.0):
     """`{name: [(t, pct), ...]}` from `start` (each battery's level now) to
-    `end`, a point at every hour edge and every block edge. A battery's list
+    `end`, a point at every hour edge, every block edge and where a battery
+    reaches its grid level or, giving, the floor. A battery's list
     stops where `sun_kwh(a, b)` is None (the sun is not known) or its
     `stop_at` comes. `sun_kwh` and `use_kwh` give kWh for the span `[a, b)`.
     Spare solar is `trust x max(0, sun - use)`, and what is stored loses
@@ -109,6 +143,7 @@ def curve(batts, start, end, sun_kwh, use_kwh, *, floor_pct, ceiling_pct,
     level = {b.name: float(b.soc) for b in batts}
     out = {b.name: [(start, level[b.name])] for b in batts}
     alive = {b.name for b in batts}
+    floor_cuts = 0
     i = 0
     while i < len(ts) - 1:
         a, z = ts[i], ts[i + 1]
@@ -147,6 +182,14 @@ def curve(batts, start, end, sun_kwh, use_kwh, *, floor_pct, ceiling_pct,
             continue
         roles = {b.name: _role(b, a, bool(want), b.name in want)
                  for b in batts if b.name in alive}
+        # A battery that gives all it holds inside the step gets a point
+        # where it reaches the floor, the same way.
+        cut = _floor_cut(a, z, net, roles, level, by, floor, hrs) \
+            if net < -EPS and floor_cuts < MAX_FLOOR_CUTS else None
+        if cut is not None:
+            floor_cuts += 1
+            ts.insert(i + 1, cut)
+            continue
         for n, to in want.items():              # charging from the grid
             b = by[n]
             room = (to - level[n]) / 100.0 * b.capacity_kwh
@@ -165,12 +208,7 @@ def curve(batts, start, end, sun_kwh, use_kwh, *, floor_pct, ceiling_pct,
                 for n, v in got.items():
                     level[n] += v * EFF / by[n].capacity_kwh * 100.0
         elif net < -EPS:
-            caps = {n: min(by[n].rating_kw * hrs,
-                           max(0.0, level[n] - floor) / 100.0
-                           * by[n].capacity_kwh * EFF)
-                    for n, r in roles.items() if r[2]}
-            first = {n: c for n, c in caps.items() if roles[n][0] == GIVE}
-            rest = {n: c for n, c in caps.items() if n not in first}
+            first, rest = _give_caps(roles, level, by, floor, hrs)
             left = -net
             for grp in (first, rest):
                 got, left = _spread(left, grp, dict(grp))
@@ -234,6 +272,9 @@ class SolarToday:
 
 
 def _hour_start(t: datetime) -> datetime:
+    """The start of `t`'s local hour, in UTC. Taken back from the UTC instant,
+    never from the wall clock, so each of the two 02:00 hours of the autumn
+    change has its own (`dayplan._hour_slices()`, SAFETY-123)."""
     lt = _local(t)
-    return lt.replace(minute=0, second=0, microsecond=0).astimezone(
-        timezone.utc)
+    return t.astimezone(timezone.utc) - timedelta(
+        minutes=lt.minute, seconds=lt.second, microseconds=lt.microsecond)

goodwe_controller/app/ui_text/en.json

@@ -456,7 +456,7 @@
       "measured_from": "Measured solar is counted from {at}, when the add-on started.",
       "tomorrow_total": "Solar expected tomorrow: {kwh}, we count on {count}.",
       "no_blocks": "No charge or give blocks planned.",
-      "give_later": "The add-on plans to give power. No block shows while the battery has no energy to give.",
+      "give_later": "The add-on plans to give power. No block shows while a battery has no energy to give.",
       "ahead": "The add-on plans about a day ahead. Blocks for later hours appear as they come near."
     },
     "region": {

goodwe_controller/app/ui_text/nl.json

@@ -384,7 +384,7 @@
       "measured_from": "Gemeten zon telt vanaf {at}, toen de add-on startte.",
       "tomorrow_total": "Verwachte zon morgen: {kwh}, we rekenen op {count}.",
       "no_blocks": "Geen laad- of leverblokken gepland.",
-      "give_later": "De add-on plant stroom te leveren. Er verschijnt geen blok zolang de batterij geen stroom heeft.",
+      "give_later": "De add-on plant stroom te leveren. Er verschijnt geen blok zolang een batterij niets kan leveren.",
       "ahead": "De add-on plant ongeveer een dag vooruit. Blokken voor latere uren verschijnen als ze naderen."
     },
     "region": {"preset": "Heffingen en btw: {region}, cijfers van {year}.", "own": "Heffingen en btw: uw eigen bedrag."},

goodwe_controller/test_ux54.py

@@ -898,6 +898,153 @@ check("F2: the same with the batteries part full and nearly full at 22:00",
           for x in o3))
 
 
+# Control walked with its own model of the packs, not the curve's levels:
+# every 15 minutes the real `_mode_roles()`; a battery in CHARGE charges at
+# its rating up to `charge_to()`; spare sun goes to the batteries whose range
+# may charge, by room, up to the ceiling; a shortfall is covered by those
+# whose range may give and whose own discharge envelope is open, by what
+# they hold above the cut-out (at the floor), each at most its rating. The
+# house is the profile the tab reads, the sun the forecast at 100 % trust.
+# Per battery and quarter tomorrow, control charges (gives) exactly where the
+# tab has a grid (give) block, both ways, no tolerance.
+def own_walk(soc, *, guard=None, sun=(0.0, 0.0)):
+    now0 = t22
+    c = S.make("dynamic", now0, soc=soc)
+    cut_out_at_floor(c)
+    floor_, ceil_ = arbitrage.soc_bounds(c.o)
+    c.tariff_plan = S.quarters(now0, night_evening, days=3)
+    c.tariff_at = now0
+    if guard is not None:
+        c.peak_guard = guard
+    c.solar_trust_pct = 100
+    c.solar_fc = fc = S.forecast(now0, sun[0], sun[1])
+    c._mode_roles(now0, None)
+    out = tab(c, now0)
+    house_w, base_w = c.house_profile.estimator()
+    d0, _d1 = homeview.local_day(now0)
+    seen = {inv.name: {} for inv in c.inverters}
+    t = now0
+    while t < d0 + timedelta(hours=48):
+        c.tariff_at = t
+        tick = c._mode_roles(t, None)
+        targets = c.plan_targets()
+        packs = {p.name: p for p in c._mode_packs()}
+        house = max(house_w(S.brussels(t).hour), base_w) / 1000.0 * 0.25
+        net = (dayview.sun_kwh(fc, now0, t, t + Q) or 0.0) - house
+        takers, givers = [], []
+        for inv in c.inverters:
+            role = tick.roles.get(inv.name)
+            lo, hi = tick.ranges.get(inv.name, (0.0, 0.0))
+            act = None
+            if role == modetrade.CHARGE:
+                to = modetrade.charge_to(packs[inv.name], ceil_, targets)
+                step = min(inv.max_w / 1000.0 * 0.25 * dayplan.EFF,
+                           max(0.0, to - inv.soc) / 100.0 * inv.capacity_kwh)
+                act = "grid" if step > 1e-9 else None
+                inv.soc += step / inv.capacity_kwh * 100.0
+            else:
+                if lo < 0.0 and inv.soc < ceil_:
+                    takers.append(inv)
+                if hi > 0.0 and may_give(inv):
+                    givers.append(inv)
+                    act = "give" if role == modetrade.GIVE else None
+            seen[inv.name][t] = act
+        if net > 0.0:
+            room = {i.name: (ceil_ - i.soc) / 100.0 * i.capacity_kwh
+                    / dayplan.EFF for i in takers}
+            tot = sum(room.values())
+            for i in takers:
+                part = min(net * room[i.name] / tot, room[i.name],
+                           i.max_w / 1000.0 * 0.25) if tot > 0.0 else 0.0
+                i.soc += part * dayplan.EFF / i.capacity_kwh * 100.0
+        elif net < 0.0:
+            hold = {i.name: max(0.0, i.soc - floor_) / 100.0 * i.capacity_kwh
+                    for i in givers}
+            tot = sum(hold.values())
+            for i in givers:
+                part = min(-net * hold[i.name] / tot,
+                           i.max_w / 1000.0 * 0.25) if tot > 0.0 else 0.0
+                i.soc = max(floor_, i.soc - part / dayplan.EFF
+                            / i.capacity_kwh * 100.0)
+        t += Q
+    return out, seen, d0
+
+
+def own_match(out, seen, d0):
+    """`[(name, kind, hour, who)]`: the quarters tomorrow where control and
+    the tab disagree (who acts there alone)."""
+    bad = []
+    for i, name in enumerate(seen):
+        for kind in ("grid", "give"):
+            blocks = [r for r in out["days"][1]["batteries"][i]["blocks"]
+                      if r["kind"] == kind]
+            for t, a in seen[name].items():
+                h = (t - d0).total_seconds() / 3600.0 - 24.0
+                if h < 0.0:
+                    continue
+                inside = any(r["start_h"] - 1e-6 <= h < r["end_h"] - 1e-6
+                             for r in blocks)
+                if (a == kind) != inside:
+                    bad.append((name, kind, round(h, 2),
+                                "control" if a == kind else "tab"))
+    return bad
+
+
+def give_span(seen, d0, name):
+    hs = [(t - d0).total_seconds() / 3600.0 - 24.0
+          for t, a in seen[name].items()
+          if a == "give" and (t - d0).total_seconds() >= 86400]
+    return (round(min(hs), 2), round(max(hs) + 0.25, 2)) if hs else None
+
+
+own = {}
+for key, soc, g, sun in (("20/20", (20.0, 20.0), None, (0.0, 0.0)),
+                         ("55/40", (55.0, 40.0), None, (0.0, 0.0)),
+                         ("90/70", (90.0, 70.0), None, (0.0, 0.0)),
+                         ("30/80", (30.0, 80.0), None, (0.0, 0.0)),
+                         ("60/60 guard", (60.0, 60.0), guard, (0.0, 0.0)),
+                         ("20/20 guard", (20.0, 20.0), guard, (0.0, 0.0)),
+                         ("30/30 guard", (30.0, 30.0), guard, (0.0, 0.0)),
+                         ("25/45 guard", (25.0, 45.0), guard, (0.0, 0.0)),
+                         ("20/20 guard 14 kWh", (20.0, 20.0), guard,
+                          (14.0, 14.0)),
+                         ("20/20 guard 6 kWh", (20.0, 20.0), guard,
+                          (6.0, 6.0)),
+                         ("20/20 8 kWh", (20.0, 20.0), None, (8.0, 8.0))):
+    o_w, s_w, d_w = own_walk(soc, guard=g, sun=sun)
+    own[key] = (o_w, s_w, d_w, own_match(o_w, s_w, d_w))
+    print(f"    own walk {key}: tab",
+          [[(r["kind"], r["from"], r["to"]) for r in b["blocks"]]
+           for b in o_w["days"][1]["batteries"]],
+          "control gives", {n: give_span(s_w, d_w, n) for n in s_w},
+          "mismatched", len(own[key][3]), own[key][3][:4])
+check("F2, control walked with its own model of the packs (not the curve's "
+      "levels): in all 11 cases it charges and gives in exactly the quarters "
+      "the tab has a block of that kind, on both batteries",
+      all(not v[3] for v in own.values()))
+o_g, s_g, d_g, _b = own["25/45 guard"]
+check("...25/45 % with the peak guard: control gives 17:00-20:15 on both "
+      "(the packs empty in the 20:00 quarter), and the tab's give block "
+      "starts at 17:00 and ends inside that quarter, at the curve's floor "
+      "point",
+      all(give_span(s_g, d_g, n) == (17.0, 20.25) for n in s_g)
+      and all([(r["kind"], r["from"]) for r in b["blocks"]] == [("give",
+                                                                 "17:00")]
+              and 20.0 < b["blocks"][0]["end_h"] <= 20.25
+              for b in o_g["days"][1]["batteries"]))
+o_6, s_6, d_6, _b = own["20/20 guard 6 kWh"]
+check("...20/20 % with the guard and 6 kWh of sun: control gives 17:00-17:15, "
+      "and the tab's give block ends inside that quarter",
+      all(give_span(s_6, d_6, n) == (17.0, 17.25) for n in s_6)
+      and all(len(b["blocks"]) == 1 and 17.0 < b["blocks"][0]["end_h"] <= 17.25
+              for b in o_6["days"][1]["batteries"]))
+fl_g = arbitrage.soc_bounds(S.make("dynamic", t22).o)[0]
+check("...and the curve has a point exactly at the floor where the block "
+      "ends (no step end)",
+      all([v for h, v in b["levels"] if abs(h - b["blocks"][0]["end_h"])
+           < 1e-3] == [fl_g] for b in o_g["days"][1]["batteries"]))
+
+
 def off_prices(h):
     if 23.0 <= h < 24.0:
         return 0.05
@@ -1065,6 +1212,19 @@ check("F2, modes off: one battery at the floor and one at 60 %: no give block "
       all(not [r for r in b if r[0] == "give"] for b in kinds(od))
       and all(not v for v in acts(sd, dd, "give").values())
       and off_match(od, sd, dd))
+c_dn = S.make("off", t22, soc=(20.0, 60.0))
+c_dn.tariff_plan = S.quarters(t22, one_quarter(13.0, 7.0), days=3)
+c_dn.tariff_at = t22
+od_nl = tab(c_dn, t22, "nl")
+check("...and B, which has energy, is not told it has none: the line names "
+      "'a battery' (the emptiest one holds the site back), EN and NL",
+      all(b["line"] == say("give_later") for b in od["days"][1]["batteries"])
+      and say("give_later").endswith(
+          "No block shows while a battery has no energy to give.")
+      and all(b["line"] == say("give_later", "nl")
+              for b in od_nl["days"][1]["batteries"])
+      and say("give_later", "nl").endswith(
+          "Er verschijnt geen blok zolang een batterij niets kan leveren."))
 # C: full at 22:00 and a cheap quarter at 01:00: the house uses some first,
 # so control charges then, and the tab has that block.
 cc, oc, sc, dc = off_sweep(one_quarter(1.0, 17.0), t22, (95.0, 95.0))

goodwe_controller/test_ux54_dst.py

@@ -0,0 +1,294 @@
+"""UX-54: the Forecast tab on the two clock-change days.
+`python3 test_ux54_dst.py`
+
+The tab walks local hours (`dayplan._hour_slices()` in `dayview` and
+`daycurve`, `SolarToday`'s hour keys). On the spring change a loop that steps
+on the wall clock never ends (SAFETY-123), and a tab request runs on the
+event loop control runs on. Graded here, every call under a hard time limit
+that the add-on's own `except Exception` cannot swallow (`Hang` is a
+`BaseException`), and a memory limit:
+
+1. The limit itself: a tab build that never returns is stopped and reported,
+   through `forecast_payload()`'s `except Exception`.
+2. `Controller.forecast_payload()` at every quarter of 27-29 March 2027 and
+   30 October-1 November 2027, modes on (Leftover solar and Cheap hours,
+   with a forecast and a house profile: the level curve) and modes off, in
+   the no-tzdata zone (`tariff._EUTimezone`) and, where the host has tzdata,
+   in ZoneInfo Europe/Brussels: it returns, `ok`, each day has 23 / 24 / 25
+   hours with the local hour labels of that day, every level inside floor
+   and ceiling, every block inside its day.
+3. `SolarToday` keeps the two 02:00 hours of the autumn change apart.
+"""
+
+import logging
+import os
+import resource
+import signal
+import sys
+from datetime import datetime, timedelta, timezone
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, HERE)
+sys.path.insert(0, os.path.join(HERE, "tools"))
+logging.disable(logging.WARNING)
+
+import ux54_scenarios as S                                        # noqa: E402
+import app.main as M                                              # noqa: E402
+from app import arbitrage, dayplan, dayview, homeview, solarfc    # noqa: E402
+from app import tariff                                            # noqa: E402
+from app.daycurve import SolarToday                               # noqa: E402
+
+UTC = timezone.utc
+fails = []
+LIMIT_S = 10.0          # one call; a build takes well under a second
+try:                    # a loop that appends without end must not take the host
+    resource.setrlimit(resource.RLIMIT_AS, (3 << 29, resource.getrlimit(
+        resource.RLIMIT_AS)[1]))
+except (ValueError, OSError):
+    pass
+
+
+def check(name, cond):
+    print(f"  {'ok  ' if cond else 'FAIL'} {name}")
+    if not cond:
+        fails.append(name)
+
+
+class Hang(BaseException):
+    """A call ran over LIMIT_S. Not an `Exception`: `forecast_payload()`
+    catches every `Exception` and would turn it into `{"ok": False}`."""
+
+
+def _alarm(*_a):
+    raise Hang()
+
+
+def limited(fn, *a, **k):
+    """`fn(*a, **k)`, or `Hang` when it takes more than LIMIT_S seconds or
+    runs out of memory."""
+    signal.signal(signal.SIGALRM, _alarm)
+    signal.setitimer(signal.ITIMER_REAL, LIMIT_S)
+    try:
+        return fn(*a, **k)
+    except MemoryError:
+        raise Hang() from None
+    finally:
+        signal.setitimer(signal.ITIMER_REAL, 0)
+
+
+# --------------------------------------------------------------------------- #
+# The clock and the zone
+# --------------------------------------------------------------------------- #
+NOW = [datetime(2027, 1, 1, tzinfo=UTC)]
+
+
+class FakeDT(datetime):
+    @classmethod
+    def now(cls, tz=None):
+        return NOW[0].astimezone(tz) if tz else NOW[0].replace(tzinfo=None)
+
+
+for _mod in (M, homeview, dayview):         # what reads the wall clock
+    _mod.datetime = FakeDT
+
+TZ_MODULES = (tariff, dayplan, homeview, solarfc)
+
+
+class zone:
+    """`BILLING_TZ` is `tz` in every module that holds it, in the block."""
+
+    def __init__(self, tz):
+        self.tz = tz
+
+    def __enter__(self):
+        self.was = [m.BILLING_TZ for m in TZ_MODULES]
+        for m in TZ_MODULES:
+            m.BILLING_TZ = self.tz
+
+    def __exit__(self, *_a):
+        for m, tz in zip(TZ_MODULES, self.was):
+            m.BILLING_TZ = tz
+
+
+ZONES = [("no tzdata (_EUTimezone)", tariff._EUTimezone())]
+try:
+    from zoneinfo import ZoneInfo
+    _bru = ZoneInfo("Europe/Brussels")
+    if datetime(2026, 7, 1, tzinfo=UTC).astimezone(_bru).hour == 2:
+        ZONES.append(("ZoneInfo Europe/Brussels", _bru))
+except Exception:                                   # noqa: BLE001
+    pass
+if len(ZONES) == 1:
+    print("    no tzdata on this host: ZoneInfo is not graded here")
+
+# The local days (UTC midnight-to-midnight instants are not used: the days
+# are known by their dates) and their hour labels.
+SPRING, AUTUMN = (2027, 3, 28), (2027, 10, 31)
+WINDOWS = (((2027, 3, 27), SPRING, (2027, 3, 29)),
+           ((2027, 10, 30), AUTUMN, (2027, 11, 1)))
+
+
+def labels_of(ymd):
+    if ymd == SPRING:
+        return ["00:00", "01:00"] + [f"{h:02d}:00" for h in range(3, 24)]
+    if ymd == AUTUMN:
+        return ["00:00", "01:00", "02:00", "02:00"] + [
+            f"{h:02d}:00" for h in range(3, 24)]
+    return [f"{h:02d}:00" for h in range(24)]
+
+
+def next_ymd(ymd):
+    d = datetime(*ymd) + timedelta(days=1)
+    return (d.year, d.month, d.day)
+
+
+def day_start_utc(ymd):
+    """Local midnight of `ymd` in UTC (CET before the change, CEST after it;
+    midnight is never inside a change)."""
+    summer = (2027, 3, 28) < ymd < (2027, 10, 31) or ymd == (2027, 10, 31)
+    if ymd == SPRING:
+        summer = False
+    return datetime(*ymd, tzinfo=UTC) - timedelta(hours=2 if summer else 1)
+
+
+# --------------------------------------------------------------------------- #
+print("1. the time limit cannot be swallowed")
+# --------------------------------------------------------------------------- #
+check("`Hang` is a BaseException and not an Exception",
+      issubclass(Hang, BaseException) and not issubclass(Hang, Exception))
+c0 = limited(S.make, "off",
+             datetime(2027, 1, 12, 11, 0, 5, tzinfo=UTC))
+_real_build = dayview.build
+
+
+def _spin(*_a, **_k):
+    while True:
+        pass
+
+
+dayview.build = _spin
+try:
+    NOW[0] = datetime(2027, 1, 12, 11, 0, 5, tzinfo=UTC)
+    got = limited(c0.forecast_payload, "en")
+except Hang:
+    got = "stopped"
+finally:
+    dayview.build = _real_build
+check("a tab build that never returns is stopped by the limit and reported, "
+      f"not turned into a page answer by forecast_payload() ({got!r})",
+      got == "stopped")
+
+# --------------------------------------------------------------------------- #
+print("\n2. the tab at every quarter of the change days")
+# --------------------------------------------------------------------------- #
+Q = timedelta(minutes=15)
+SCENARIOS = (("modes on", "dynamic", (55.0, 40.0)),
+             ("modes off", "off", (55.0, 40.0)))
+
+
+def wrong(out, ymd, floor_, ceil_):
+    """What is wrong with one build, or None."""
+    if not out.get("ok") or len(out.get("days") or []) != 2:
+        return "not ok"
+    for k, day in enumerate(out["days"]):
+        exp = labels_of((ymd, next_ymd(ymd))[k])
+        hrs = day["hours"]
+        if day["length_h"] != len(exp):
+            return f"day {k}: length {day['length_h']}"
+        if [h["label"] for h in hrs] != exp:
+            return f"day {k}: labels"
+        if any(abs(h["end_h"] - h["start_h"] - 1.0) > 1e-6
+               or abs(h["start_h"] - j) > 1e-6 for j, h in enumerate(hrs)):
+            return f"day {k}: hour spans"
+        for b in day["batteries"]:
+            if any(not floor_ - 1e-6 <= v <= ceil_ + 1e-6
+                   or not -1e-6 <= h <= len(exp) + 1e-6
+                   for h, v in b["levels"]):
+                return f"day {k}: level {b['name']}"
+            if any(not 0.0 <= r["start_h"] <= r["end_h"] <= len(exp) + 1e-6
+                   for r in b["blocks"]):
+                return f"day {k}: block {b['name']}"
+    return None
+
+
+def walk(scn, soc):
+    """`(builds, with a curve, stopped, wrong)` over every quarter of the
+    six local days; the first call stopped by the limit ends the walk."""
+    builds, curves, bad = 0, 0, []
+    for window in WINDOWS:
+        for ymd in window:
+            a = day_start_utc(ymd)
+            z = day_start_utc(next_ymd(ymd))
+            t = a + timedelta(seconds=5)
+            try:
+                NOW[0] = t
+                c = limited(S.make, scn, t, soc=soc)
+                floor_, ceil_ = arbitrage.soc_bounds(c.o)
+                while t < z:
+                    NOW[0] = t
+                    c.tariff_at = t
+                    if c.modes_on:
+                        limited(c._mode_roles, t, None)
+                    limited(c.solar_today.add, t, 1500.0)
+                    out = limited(c.forecast_payload, "en")
+                    builds += 1
+                    curves += any(len(b["levels"]) > 1
+                                  for d in out.get("days") or []
+                                  for b in d["batteries"])
+                    why = wrong(out, ymd, floor_, ceil_)
+                    if why:
+                        bad.append((t.isoformat(), why))
+                    t += Q
+            except Hang:
+                return builds, curves, t.isoformat(), bad
+    return builds, curves, None, bad
+
+
+for zname, tz in ZONES:
+    with zone(tz):
+        for label, scn, soc in SCENARIOS:
+            builds, curves, stopped, bad = walk(scn, soc)
+            print(f"    {zname}, {label}: {builds} builds ({curves} with a "
+                  f"level curve), stopped at {stopped}, {len(bad)} wrong "
+                  f"{bad[:3]}")
+            check(f"{zname}, {label}: the tab returns at every quarter of "
+                  "27-29 March and 30 October-1 November 2027 (under "
+                  f"{LIMIT_S:g} s each), and each day has its 23, 24 or 25 "
+                  "hours, labelled, levels inside floor and ceiling, blocks "
+                  "inside the day",
+                  stopped is None and not bad
+                  and builds == (96 + 92 + 96) + (96 + 100 + 96)
+                  and (curves == builds if scn == "dynamic" else not curves))
+
+# --------------------------------------------------------------------------- #
+print("\n3. measured solar keeps the two autumn 02:00 hours apart")
+# --------------------------------------------------------------------------- #
+for zname, tz in ZONES:
+    with zone(tz):
+        s = SolarToday()
+        a = day_start_utc(AUTUMN)            # 00:00 CEST = 22:00 UTC
+        t = a
+        while t <= a + timedelta(hours=4):
+            # 1 kW in the first 02:00 hour (00:00-01:00 UTC), 3 kW in the
+            # second (01:00-02:00 UTC), nothing else
+            w = 1000.0 if a + timedelta(hours=2) <= t < a + timedelta(
+                hours=3) else 3000.0 if a + timedelta(hours=3) <= t < a + \
+                timedelta(hours=4) else 0.0
+            limited(s.add, t, w)
+            t += timedelta(minutes=1)
+        now = a + timedelta(hours=4, minutes=30)
+        sl = [x for x in limited(dayplan._hour_slices, a, now)
+              if x[2] == 2]
+        got = [None if x is None else round(x, 2) for x in
+               (limited(s.kwh, x[0], x[1], now) for x in sl)]
+        print(f"    {zname}: the two 02:00 hours {got}")
+        check(f"{zname}: two 02:00 slices, about 1 kWh and 3 kWh, each in "
+              "its own hour", len(sl) == 2 and got[0] is not None
+              and got[1] is not None and abs(got[0] - 1.0) < 0.06
+              and abs(got[1] - 3.0) < 0.06)
+
+print()
+if fails:
+    print(f"{len(fails)} FAILED")
+    sys.exit(1)
+print("all passed")