Backfill guard: a past week's digest only takes papers published by its end

Backfilling an old week used to sweep in undigested papers published later
(stamping them into the wrong week and removing them from the next Monday's
digest); regular weekly runs are unaffected since the collection window
already ends at week_end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_pipeline.py

@@ -84,6 +84,18 @@ def test_build_payload_invalid_feed_spec_is_a_gap(env):
     assert any("invalid feed spec" in g for g in payload.data_gaps)
 
 
+def test_backfill_excludes_papers_published_after_the_week(env):
+    # 과거 주 소급 생성: 그 주 이후에 발행된 미소화 논문은 과거 다이제스트로 끌려가면 안 된다
+    from datetime import date
+
+    in_week = make_paper("10.1/inweek", published_date=date(2026, 9, 2))
+    later = make_paper("10.1/later", published_date=date(2026, 9, 20))  # W36 이후 발행
+    undated = make_paper("10.1/undated", published_date=None)
+    env["store"].pending = [in_week, later, undated]
+    payload = build_payload(WEEK, env["settings"], env["store"])  # WEEK = 2026-W35 (…~09-06)
+    assert [p.doi for p in payload.papers] == ["10.1/inweek", "10.1/undated"]
+
+
 def test_build_payload_caps_papers_and_notes_rollover(env):
     env["store"].pending = [make_paper(f"10.1/p{i}") for i in range(5)]
     env["settings"] = env["settings"].model_copy(update={"max_papers": 3})