test(reconcile): a span across a segment edge leaves neither segment holding a replaced word -- a mutation that skipped this survived

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/reconcile/reconcile_spots_test.go

@@ -118,3 +118,13 @@ func TestReconcileSegments_SegmentsThatDoNotLineUpWithTheTextAreLeftAsTheBases(t
 	assert.Equal(t, base.Segments, out.Segments)
 	assert.Equal(t, "a y b c", out.Text, "the merged text is unaffected")
 }
+
+func TestReconcileSegments_ASpanThatCrossesASegmentEdgeIsRemovedFromBothSegments(t *testing.T) {
+	base := segmented("a b c d", domain.Segment{Start: 0, End: 5, Text: "a b"}, domain.Segment{Start: 5, End: 10, Text: "c d"})
+
+	out := merge(t, base, tr("a X d"), always(reconcile.VerdictAlt))
+
+	require.Equal(t, "a X d", out.Text)
+	assert.Equal(t, "a X", out.Segments[0].Text)
+	assert.Equal(t, "d", out.Segments[1].Text, "'c' was replaced too: it must not linger in the second segment")
+}