fix(sp41): test has_overridden_visits + clarify pipeline_b forward-compat helper

backend/src/cyclone/rebill/pipeline_b.py

@@ -20,8 +20,11 @@ from cyclone.rebill.timely_filing import timely_filing_decision
 @dataclass(frozen=True)
 class MemberWeekBatch:
     """Pre-emission 837P shape for Pipeline B. The orchestrator's serializer
-    adapter converts this to a ClaimOutput for serialize_837 (one 837P
+    adapter converts this to a ClaimOutput for serialize_837.
-    carrying every visit in `visits` as a CLM segment).
+
+    Note: frozen=True is shallow — `visits` is a mutable list, so
+    `mb.visits.append(x)` works even though `mb.visits = new_list` raises
+    FrozenInstanceError. Treat the batch as logically immutable.
     """
 
     member_id: str
@@ -78,7 +81,12 @@ def batch_visits_by_member_week(
     ISO-week) batches back down to a per-member visit list. This is the
     shape the orchestrator's summary aggregation expects.
 
-    NOTE: This collapses multiple weeks for the same member into one
+    PROVISIONAL: this helper is defined for the Task 12 orchestrator's
+    anticipated use, but has no callers in this branch. If Task 12's
+    actual needs differ, this function may be removed or replaced without
+    notice.
+
+    This also collapses multiple weeks for the same member into one
     list. If the orchestrator needs week-aware per-member iteration,
     use build_pipeline_b_batches directly.
     """

backend/tests/test_rebill_pipeline_b.py

@@ -39,3 +39,37 @@ def test_override_relaxes_timely_filing():
     out_overridden = build_pipeline_b_batches(visits, as_of=date(2026, 7, 7), override=True)
     assert out_default == []
     assert len(out_overridden) == 1
+
+
+def test_override_flag_set_on_past_window_visit_batch():
+    # Same member "OLD" with one past-window visit (187 days old, ISO
+    # week 1) and one within-window visit (10 days old, ISO week 26).
+    # With override=True the past-window visit survives and the batch
+    # for week 1 must be flagged has_overridden_visits=True because the
+    # override saved an otherwise-excluded visit.
+    visits = [
+        _v(date(2026, 1, 1), "OLD", "T1019", "2.32"),  # 187 days old (past window, W01)
+        _v(date(2026, 6, 27), "OLD", "T1019", "2.32"),  # 10 days old (within window, W26)
+    ]
+    out_overridden = build_pipeline_b_batches(
+        visits, as_of=date(2026, 7, 7), override=True,
+    )
+    # Two batches: one per (member, ISO-week) — the past-window visit and
+    # the within-window visit land in different weeks.
+    assert len(out_overridden) == 2
+    by_week = {b.iso_week: b for b in out_overridden}
+    assert by_week[1].member_id == "OLD"
+    assert by_week[1].has_overridden_visits is True  # the override saved this batch
+    assert by_week[26].member_id == "OLD"
+    assert by_week[26].has_overridden_visits is False  # no override needed here
+
+    # With override=False the past-window visit is dropped. The surviving
+    # within-window batch (W26) must NOT carry the override flag, and the
+    # past-window batch (W01) is absent.
+    out_default = build_pipeline_b_batches(
+        visits, as_of=date(2026, 7, 7), override=False,
+    )
+    assert len(out_default) == 1
+    assert out_default[0].member_id == "OLD"
+    assert out_default[0].iso_week == 26
+    assert out_default[0].has_overridden_visits is False