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

tests/fixtures/README.md

@@ -47,6 +47,30 @@ structurally valid input, silently reduced output, exit code 0 and no warning:
   the xlsx extracts with the sheet name intact and **every cell value gone**.
   The fixture therefore uses a `dimension` element and a shared string table.
 
+## The proposer's default-profile golden
+
+`propose-golden-default.json` is the artifact `tools/okf_propose_segments.py`
+produces for `OUTLINE_DOCUMENT` (defined in `tests/test_propose_segments.py`)
+with **no flags at all**, generated at commit `798f64a` with
+`--proposed-at 2026-09-03T00:00:00Z`. The timestamp is an explicit argument
+because the artifact carries it verbatim; a wall-clock default would make the
+golden unreproducible by construction.
+
+**Why the fixture is `OUTLINE_DOCUMENT` and not `DOCUMENT`.** The golden exists
+to go red if any later rule is accidentally defaulted ON. `DOCUMENT` was
+measured to contain **zero** bare-integer lines, so a golden over it would stay
+byte-identical through exactly the regression it was named to catch -- a trap
+written down but unable to fire. `OUTLINE_DOCUMENT` carries a bare-integer
+ascending run of three, which today's rules do not match (measured: bare `1` /
+`1.` / `1)` yield 0 candidates), so the golden pins that absence and breaks the
+moment it stops being true.
+
+**It transitively pins `observed_extractor_version`**
+(`src/llm_ingestion_okf/segmentation.py`): the field is written into every
+artifact, so a converter or extractor bump turns this golden red. That red is
+legitimate -- read the diff and decide, exactly as for the frozen PDF literal
+below. Regenerate only after that decision, never to make a red go away.
+
 ## Why the expected office text is frozen as a literal
 
 The same reason as the PDF text below, with one addition: the literals are