test(propose): pin the default artifact with a committed golden

tests/test_propose_segments.py

@@ -52,6 +52,42 @@ Hovedbaeresystemet skal ha R60 dokumentert baereevne.
 """
 
 
+#: The golden fixture's document. It carries a BARE-INTEGER ascending run of
+#: three (`1`, `2`, `3`), which today's rules do not match at all -- measured,
+#: bare `1` / `1.` / `1)` yield 0 candidates. That is precisely why the golden
+#: is taken over THIS text and not over `DOCUMENT`: `DOCUMENT` has no
+#: bare-integer line, so a golden over it would stay byte-identical even if the
+#: outline rule were accidentally defaulted ON, and the guard would be a trap
+#: written down but never able to fire. The ATX heading and the dotted heading
+#: are here so the shipping rules fire too, and the golden pins their output as
+#: well as the outline rule's absence.
+OUTLINE_DOCUMENT = """# Stange skole -- teknisk grunnlag
+
+Innledende tekst som gir dokumentet en kropp foer kapitlene begynner.
+
+1 Innledning
+
+Bakgrunnen for prosjektet og omfanget av arbeidet.
+
+2 Krav
+
+Krav til seksjonering av bygget over flere etasjer.
+
+3 Gjennomfoering
+
+Framdrift, faser og overlevering av bygget.
+
+1.1 Brannkonsept
+
+To uavhengige roemningsveier fra hver branncelle.
+"""
+
+#: Frozen in the golden's bytes. An explicit argument because the artifact
+#: carries it verbatim, and a wall-clock default would make the golden
+#: unreproducible by construction.
+GOLDEN_PROPOSED_AT = "2026-09-03T00:00:00Z"
+
+
 def write(tmp_path: Path, text: str = DOCUMENT, name: str = "n500.md") -> Path:
     path = tmp_path / name
     path.write_text(text, encoding="utf-8", newline="")
@@ -511,3 +547,31 @@ def test_an_unbreakable_line_longer_than_the_cap_is_still_cut(
     for entry in plan["entries"]:
         start, end = entry["span"]
         assert end - start <= 3000
+
+
+# --- the default profile, pinned byte for byte ----------------------------
+#
+# The one guard that can go red on an accidental default-on regression of any
+# rule added later. It compares the WHOLE artifact, so a new candidate, a moved
+# span, a changed `derived` list or a renamed path all break it.
+
+
+def test_the_default_artifact_matches_its_committed_golden(tmp_path: Path) -> None:
+    """The default profile is a promise to consumers; this is what keeps it.
+
+    The golden transitively pins `observed_extractor_version` too, so a
+    converter bump turns this red. That is a legitimate red, not a defect:
+    read the diff and decide, per `tests/fixtures/README.md`.
+    """
+    source = write(tmp_path, OUTLINE_DOCUMENT, "outline.md")
+    out = tmp_path / "outline-plan.json"
+    assert (
+        okf_propose_segments.main(
+            [str(source), "--out", str(out), "--proposed-at", GOLDEN_PROPOSED_AT]
+        )
+        == 0
+    )
+    golden = Path(__file__).parent / "fixtures" / "propose-golden-default.json"
+    assert out.read_bytes() == golden.read_bytes(), (
+        "the default artifact diverges from its committed golden bytes"
+    )