feat(m2): add append-only decision log and beslutning skill

tests/test_beslutninger_log.py

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+"""The append-only sourcing-decision store (plan Step 22).
+
+Build-brief 5.4 is a schema, and this file is what keeps it one. The store
+cannot be migrated -- that is the whole consequence of append-only (risk H10) --
+so every rule it will ever have has to hold on the first line written, and the
+fixture corpus under `tests/fixtures/beslutninger/` is the fasit the writer is
+measured against rather than a sample it may drift from.
+
+Four of the six rules below exist because the field they guard is read much
+later by something that cannot ask again:
+
+* **`score_da` is an integer.** M6 reads it as a value on a weight-dependent
+  scale (risk M8r). A string that looks like a number sorts as text and
+  averages as nothing.
+* **One to three reasons, from the closed twelve.** `laering` proposes only on
+  "the same `arsak` in at least four of twenty". A thirteenth reason invented
+  at write time is a category that can never reach that threshold and never be
+  counted against it either.
+* **A note is at most fifteen words.** The cap is what keeps the field a label
+  rather than a second body, and build-brief 5.4 states it as a number.
+* **A correction names a decision that exists.** `jsonl.fold` raises when it
+  meets a correction pointing at nothing; catching it at write time is the
+  difference between a refusal and a log that cannot be read afterwards.
+
+Style note: this file follows tests/test_jsonl.py.
+"""
+
+import json
+import os
+
+import pytest
+
+import beslutninger
+from jobbsok_lib import jsonl
+
+
+def beslutning(**overrides):
+    record = {
+        "id": "b-0001",
+        "dato": "2026-09-01T09:00:00+02:00",
+        "kilde": "manuell",
+        "url": "https://stillinger.example/sak-0001",
+        "tittel": "Dataingeniør",
+        "arbeidsgiver": "Værøy Sjømat AS",
+        "beslutning": "ja",
+        "arsak": ["fagomrade", "teknologi"],
+        "notat": "treffer kjernen",
+        "score_da": 78,
+        "delscore": {"fagomrade": 78, "oppgavetype": 73, "teknologi": 68, "selskapstype": 63},
+        "vekter": {"fagomrade": 40, "oppgavetype": 30, "teknologi": 20, "selskapstype": 10},
+        "vekt_hash": "sha256:" + "e4" * 32,
+    }
+    record.update(overrides)
+    return record
+
+
+def test_an_append_adds_one_line_and_leaves_prior_bytes_unchanged(empty_workspace):
+    sti = beslutninger.sti(empty_workspace)
+    beslutninger.legg_til(empty_workspace, beslutning(id="b-0001"))
+    with open(sti, "rb") as handle:
+        forst = handle.read()
+
+    beslutninger.legg_til(empty_workspace, beslutning(id="b-0002", beslutning="nei",
+                                                     arsak=["lonn"]))
+    with open(sti, "rb") as handle:
+        etter = handle.read()
+
+    # Not "the file still parses" -- the earlier bytes must be the same bytes.
+    assert etter.startswith(forst)
+    assert etter[len(forst):].count(b"\n") == 1
+    assert [rec["id"] for rec in beslutninger.les(empty_workspace)] == ["b-0001", "b-0002"]
+
+    # And the line carries the two fields no later migration can add.
+    forste = json.loads(forst.decode("utf-8"))
+    assert forste["type"] == "beslutning" and forste["skjema"] == jsonl.SKJEMA
+    assert list(forste) == list(beslutninger.FELTREKKEFOLGE), (
+        "the record is laid out as %r; the fixture corpus is the fasit and it "
+        "lays it out as %r" % (list(forste), list(beslutninger.FELTREKKEFOLGE))
+    )
+
+
+def test_one_to_three_reasons_from_the_enum_are_accepted_and_nothing_else_is(
+    empty_workspace,
+):
+    for arsak in (["lonn"], ["lonn", "geografi"], ["lonn", "geografi", "annet"]):
+        record = beslutninger.legg_til(
+            empty_workspace,
+            beslutning(id="b-%d" % len(arsak) + "-".join(arsak), arsak=arsak),
+        )
+        assert record["arsak"] == arsak
+
+    for ugyldig in ([], ["lonn", "geografi", "annet", "tidspunkt"], ["pendling"],
+                    ["lonn", "lonn"], "lonn"):
+        with pytest.raises(beslutninger.BeslutningError) as fanget:
+            beslutninger.legg_til(empty_workspace, beslutning(id="b-avvist", arsak=ugyldig))
+        assert "arsak" in str(fanget.value)
+
+    # The refusal leaves nothing behind: validation runs before the file opens.
+    assert [rec["id"] for rec in beslutninger.les(empty_workspace)] == [
+        "b-1lonn", "b-2lonn-geografi", "b-3lonn-geografi-annet"
+    ]
+
+
+def test_a_note_longer_than_fifteen_words_is_refused(empty_workspace):
+    akkurat = " ".join("ord%d" % n for n in range(beslutninger.MAKS_NOTAT_ORD))
+    record = beslutninger.legg_til(empty_workspace, beslutning(notat=akkurat))
+    assert record["notat"] == akkurat
+
+    ett_for_mye = akkurat + " overflodig"
+    with pytest.raises(beslutninger.BeslutningError) as fanget:
+        beslutninger.legg_til(empty_workspace, beslutning(id="b-lang", notat=ett_for_mye))
+    assert "15" in str(fanget.value), (
+        "the refusal must name the cap it enforced: %r" % (str(fanget.value),)
+    )
+
+
+def test_score_da_must_be_an_integer(empty_workspace):
+    for ugyldig in ("78", 78.5, None, True):
+        with pytest.raises(beslutninger.BeslutningError) as fanget:
+            beslutninger.legg_til(
+                empty_workspace, beslutning(id="b-score", score_da=ugyldig)
+            )
+        assert "score_da" in str(fanget.value)
+
+    record = beslutninger.legg_til(empty_workspace, beslutning(score_da=0))
+    assert record["score_da"] == 0 and isinstance(record["score_da"], int)
+
+
+def test_a_correction_must_reference_a_decision_that_exists(empty_workspace):
+    beslutninger.legg_til(empty_workspace, beslutning(id="b-0001", arsak=["lonn"]))
+
+    with pytest.raises(beslutninger.BeslutningError) as fanget:
+        beslutninger.korriger(
+            empty_workspace,
+            {"id": "k-0001", "dato": "2026-09-02T09:00:00+02:00",
+             "korrigerer": "b-finnes-ikke", "arsak": ["geografi"]},
+        )
+    assert "b-finnes-ikke" in str(fanget.value)
+
+    rettelse = beslutninger.korriger(
+        empty_workspace,
+        {"id": "k-0001", "dato": "2026-09-02T09:00:00+02:00",
+         "korrigerer": "b-0001", "arsak": ["geografi"],
+         "notat": "reisevei var den egentlige grunnen"},
+    )
+    assert rettelse["type"] == "korrigering"
+
+    # A correction is a new line, never an edit: both are still on disk, and
+    # the folded stream shows the corrected decision rather than two rows.
+    linjer = beslutninger.les(empty_workspace)
+    assert [rec["id"] for rec in linjer] == ["b-0001", "k-0001"]
+    strom = beslutninger.stromme(empty_workspace)
+    assert len(strom) == 1
+    assert strom[0]["id"] == "b-0001" and strom[0]["arsak"] == ["geografi"]
+
+
+def test_the_case_identifier_from_a_norwegian_employer_is_pure_ascii():
+    sak_id = beslutninger.sak_id_for(beslutning())
+    assert sak_id == "2026-09-vaeroy-sjomat-as-dataingenior"
+    sak_id.encode("ascii")  # raises if a macOS NFD byte survived (risk H8)
+
+    # And the hand-off only happens on a yes: a `nei` creates no case at all.
+    assert beslutninger.sak_id_for(beslutning(beslutning="nei")) is None