feat(segmentation): quote anchors so a re-extraction costs a re-anchor

tests/test_segmentation.py

@@ -451,3 +451,83 @@ def test_slicing_an_empty_text_with_any_span_is_refused() -> None:
     with pytest.raises(SegmentationError) as excinfo:
         slice_segments("", five_section_plan(spans=((0, 1),)))
     assert excinfo.value.code == "segmentation_span_invalid"
+
+
+# --- S5c: the quote anchor, which survives a shift the key must not refuse --
+#
+# The key (S5b, above) refuses a FOREIGN extraction. This is the other half:
+# a benign shift INSIDE the same extraction, where the text an entry names is
+# still present but no longer at the offset written down. Measured: changing
+# one extraction flag moved a document from 15 507 to 8 290 characters and
+# every inspected span pointed at the wrong text. Offsets are therefore a HINT
+# the quote may correct -- never the last word, and never silently wrong.
+
+
+ANCHORED = "innledning\n" + SECTIONS
+
+
+def anchored_entry(index: int, **overrides: Any) -> dict[str, Any]:
+    start, end = SPANS[index]
+    quote = SECTIONS[start:end]
+    payload = entry(
+        segment_id=f"s{index}",
+        path=f"krav/{index}-del.md",
+        span=[start, end],
+        anchor={
+            "quote": quote,
+            "prefix": SECTIONS[max(0, start - 12) : start],
+            "suffix": SECTIONS[end : end + 12],
+        },
+    )
+    payload.update(overrides)
+    return payload
+
+
+def anchored_plan(*indexes: int, **overrides: Any) -> SegmentationPlan:
+    return parse_segmentation_plan(
+        plan(entries=[anchored_entry(index) for index in indexes], **overrides)
+    )
+
+
+def test_an_anchor_whose_offsets_still_hold_changes_nothing() -> None:
+    """The fast path. A correct plan must not be re-anchored into motion."""
+    sliced = slice_segments(SECTIONS, anchored_plan(1, 2))
+    assert [body for _, body in sliced] == [SECTIONS[34:73], SECTIONS[73:106]]
+    assert [item.span for item, _ in sliced] == [(34, 73), (73, 106)]
+
+
+def test_stale_offsets_re_anchor_to_the_text_the_quote_names() -> None:
+    """The whole point: the same document with eleven characters prepended.
+
+    Every declared offset is now short by exactly that much. Without the
+    anchor each body would be cut eleven characters early and land on real
+    text -- the failure no downstream assertion can see.
+    """
+    sliced = slice_segments(ANCHORED, anchored_plan(1, 2))
+    assert [body for _, body in sliced] == [SECTIONS[34:73], SECTIONS[73:106]]
+    assert [item.span for item, _ in sliced] == [(45, 84), (84, 117)]
+
+
+def test_a_quote_that_no_longer_occurs_is_refused_rather_than_cut_elsewhere() -> None:
+    """Refusing beats cutting. A body sliced at a plausible-but-wrong offset
+    reads as ordinary prose, so nothing downstream can distinguish it from an
+    adjudicated one."""
+    gone = SECTIONS.replace("1 Brannkonsept: krav til seksjonering.\n", "")
+    with pytest.raises(SegmentationError) as excinfo:
+        slice_segments(gone, anchored_plan(1))
+    assert excinfo.value.code == "segmentation_span_invalid"
+    assert "s1" in str(excinfo.value)
+
+
+def test_a_repeated_quote_re_anchors_to_the_occurrence_its_context_names() -> None:
+    """Prefix and suffix are what make a repeated line addressable at all."""
+    doubled = "xx" + SECTIONS + SECTIONS
+    sliced = slice_segments(doubled, anchored_plan(1))
+    assert sliced[0][0].span == (36, 75)
+    assert sliced[0][1] == SECTIONS[34:73]
+
+
+def test_an_entry_without_an_anchor_keeps_todays_offset_behaviour() -> None:
+    """The anchor is a capability, not a new requirement on authored plans."""
+    sliced = slice_segments(SECTIONS, five_section_plan())
+    assert [item.span for item, _ in sliced] == list(SPANS)