FCST-05: one byte stops stopping the add-on, and the write path gets the read path's standard

HIGH - a non-UTF-8 byte in /data/price_history.json stopped the add-on
from starting. `_load()` caught `(json.JSONDecodeError, OSError)`.
`UnicodeDecodeError` is `ValueError -> UnicodeError -> UnicodeDecodeError`:
neither of those, and `issubclass(UnicodeDecodeError, OSError)` is False. So
it escaped `_load()` -> `_open()` -> `PriceHistory.__init__`, which
`Controller.__init__` does not guard - breaking `_load()`'s own stated
contract, "a corrupt cache must not stop the controller". The handler now
names the ValueError FAMILY (the file's content) beside OSError (its bytes),
because a third subclass nobody has thought of is how this arrived the first
time. The suite could not see it: its "unreadable file" fixture writes
"{ this is not json", which is valid UTF-8 and fails one step later, in
`json`. A fixture holding a genuinely undecodable byte is now beside it,
with the difference between the two asserted as a precondition.

MEDIUM - a malformed `start` under the day the feed is writing to killed the
tariff plan permanently. `_remember()` merged with `{q["start"]: q ...}` and
sorted on `q["start"]`, trusting a value read off /data to be a hashable,
sortable string. An int, null, a dict or a list raised TypeError out of
`carry()` -> `resolve_tariff()` -> `run_tariff_refresh`, which catches
Exception - so the add-on stayed UP while every refresh raised forever, the
plan retiring after TARIFF_MAX_AGE_S with arbitrage and the cheap window off
for good, and no self-heal because `_remember()` raised before `_save()`.
The read path was properly defensive throughout, which is why `yesterday()`
survived and the existing fixture passed - it files its malformed rows under
a day the feed is NOT writing to. Both paths now share one validator,
`_point_of()`. A row that is not a point is dropped, reported, and written
back out clean.

...and the status row said the store was healthy while the plan was dead:
`words` read '2026-01-15 (1 h)'. `_load()` now counts the rows inside a kept
record as well as the record itself, so the store stops reporting plain
health from the moment it is opened; the note names what was FOUND at open
and what was DROPPED by the refresh, and clears once the file is rewritten.

...and the merge key is the validated INSTANT rather than its spelling,
which is what rule 4 already said. The lexicographic sort beside the string
key also put the second 02:00 of the 25-hour October day (+01:00) before the
first (+02:00); stored order only, since `_parse_points()` re-sorts.

LOW - the status row counted POINTS and printed them under the HOUR's name:
'2026-01-13 (96 h)' for a 24-hour day on the quarter-hourly feed this add-on
already supports. It is now '96 points over 24 h' - two facts, each under
its own unit.

LOW - two stated reasons were false. `_audit`'s "WHY IT IS STRICTER" claimed
the rework refused the same published point emitted twice and a carried
point sharing a published hour, "which the old count never looked at". A
differential over the whole domain the audit can express finds ZERO
divergence in both directions: the old `seen` count already refused the
first (one point twice is one hour twice) and the old IDENTITY rule already
refused the second. The reworked audit is EQUAL to FCST-03's, not stronger;
the only behavioural change is the intended relaxation, and it stays. The
differential is committed as a check rather than left as prose.

...and the audit's real limit is named: it does not check COMPLETENESS. Fed
the decimation defect FCST-04 was raised for it ACCEPTS, and it accepts an
empty output. So `_audit` is not what stops that recurring - the count and
identity checks are, and the text now points at them. Not made complete:
`published` is the whole read while the fill emits only [since, until), so
the rule as stated is wrong, and building it takes the 1/12/48 h horizon
checks red on a healthy feed. Measured, not assumed.

12 mutations, purged tree, every one RED, no survivors. All 29 test files
green. Nothing deployed; no option added; config.yaml untouched.

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

goodwe_controller/MUTATION.md

@@ -127,6 +127,21 @@ Two rules come out of it, and both are cheap:
    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.
+
 ## 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