test(m1): add conftest fixtures and golden helpers

tests/helpers/workspace.py

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+"""Workspace construction and corpus-integrity helpers (plan Step 6).
+
+`make_case` builds the case shape from build-brief 5.2 and 5.3 so tests can
+say what they need in one line instead of laying out directories by hand.
+`snapshot_tree` and `assert_tree_unchanged` are the machinery behind
+conftest's autouse pristine guard: a test that writes into the fixture corpus
+poisons every later run, and the failure would otherwise surface far from its
+cause.
+
+Note on the case log: entries here carry `hendelse` from the build-brief 5.3
+enum and are written with a single append, mirroring
+`jobbsok_lib.jsonl.append_line`'s contract without going through its
+`type` validation -- that closed set (`beslutning`, `korrigering`, `utfall`)
+is the decision log's discriminator, and the case log has its own. Step 17
+defines the event enum properly; until then this helper does not force a
+decision-log type onto a case event. Reading goes back through
+`jsonl.read_lines`, so the torn-line and corruption rules still apply.
+"""
+
+import datetime
+import json
+import os
+
+from jobbsok_lib import frontmatter as frontmatter_lib
+from jobbsok_lib import jsonl, paths
+
+#: The frozen date the whole suite reasons from, as an aware instant. Norway
+#: is on CEST (+02:00) on this date, and the offset is written out rather than
+#: derived, so the fixtures do not depend on the machine's timezone database.
+FROZEN_TODAY = "2026-09-15"
+FROZEN_NOON = datetime.datetime.fromisoformat(FROZEN_TODAY + "T12:00:00+02:00")
+
+
+def event(hendelse, days_ago=0, kilde=None, ref=None, notat=None):
+    """A build-brief 5.3 case-log record, dated relative to the frozen today."""
+    moment = FROZEN_NOON - datetime.timedelta(days=days_ago)
+    return {
+        "ts": moment.isoformat(),
+        "hendelse": hendelse,
+        "kilde": kilde,
+        "ref": ref,
+        "notat": notat,
+    }
+
+
+def make_case(root, arbeidsgiver, rolle, year_month, events=(), **fields):
+    """Create ``saker/<sak-id>/`` with a sak.md and a logg.jsonl.
+
+    Returns the `sak-id`, which is derived through :func:`paths.sak_id` rather
+    than assembled here -- the slug rules are that module's contract and a
+    second implementation would drift from it.
+    """
+    sak_id = paths.sak_id(year_month, arbeidsgiver, rolle)
+    case_dir = paths.safe_join(root, "saker", sak_id)
+    os.makedirs(case_dir, exist_ok=True)
+
+    metadata = {
+        "sak_id": sak_id,
+        "arbeidsgiver": arbeidsgiver,
+        "rolle": rolle,
+        "opprettet": FROZEN_TODAY,
+        "status": "vurderes",
+        "ventende_part": "meg",
+    }
+    metadata.update(fields)
+    with open(os.path.join(case_dir, "sak.md"), "w", encoding="utf-8") as handle:
+        handle.write(frontmatter_lib.render(metadata, "## Hvorfor denne\n\n"))
+
+    log = os.path.join(case_dir, "logg.jsonl")
+    for record in events:
+        _append_raw(log, record)
+    if not events:
+        open(log, "a", encoding="utf-8").close()
+    return sak_id
+
+
+def read_jsonl(path):
+    """Read a JSONL file through the real reader, torn-line rules and all."""
+    return jsonl.read_lines(path)
+
+
+def frontmatter(path):
+    """Parse a file's frontmatter, returning ``(metadata, body)``."""
+    with open(path, "r", encoding="utf-8") as handle:
+        return frontmatter_lib.parse(handle.read())
+
+
+def snapshot_tree(root):
+    """Map every file under ``root`` to the pair that betrays a mutation.
+
+    Size catches an edit that changes length, modification time catches one
+    that does not. Neither alone is enough, and a content hash would make the
+    autouse guard cost real time on every test in the suite.
+    """
+    snapshot = {}
+    for dirpath, _dirnames, filenames in os.walk(root):
+        for name in filenames:
+            full = os.path.join(dirpath, name)
+            info = os.stat(full)
+            snapshot[os.path.relpath(full, root)] = (info.st_size, info.st_mtime_ns)
+    return snapshot
+
+
+def assert_tree_unchanged(root, before):
+    """Fail if anything under ``root`` was added, removed or modified."""
+    after = snapshot_tree(root)
+    added = sorted(set(after) - set(before))
+    removed = sorted(set(before) - set(after))
+    changed = sorted(name for name in set(before) & set(after) if before[name] != after[name])
+    if not (added or removed or changed):
+        return
+    raise AssertionError(
+        "the fixture corpus under %r was mutated by a test -- added=%r "
+        "removed=%r changed=%r. Fixtures are read-only; copy into tmp_path "
+        "instead." % (root, added, removed, changed)
+    )
+
+
+def _append_raw(path, record):
+    payload = (json.dumps(record, ensure_ascii=False) + "\n").encode("utf-8")
+    handle = os.open(path, os.O_WRONLY | os.O_APPEND | os.O_CREAT, 0o600)
+    try:
+        os.write(handle, payload)
+    finally:
+        os.close(handle)