fix: tolerate backfill under-delivery, fix predict None-fill, drop dead session_id

tests/unit/test_adversarial_iteration.py

@@ -163,3 +163,29 @@ async def test_rounds_backfill_then_stop_at_max(tmp_path):
     ids = {d["question_id"] for d in json.loads(final_path.read_text(encoding="utf-8"))}
     assert "q0" in ids and any(x.startswith("bf0_") for x in ids)
     store.close()
+
+
+@pytest.mark.asyncio
+async def test_rounds_tolerate_backfill_under_delivery(tmp_path):
+    """backfill 欠产（实得 < deficit，被 gate 拒常态）→ 不崩，并入实得题，达上限停。"""
+    store = QuestionGenStore(str(tmp_path / "q.db"))
+    agent = _FakeAgent(pred="B")
+    # 每轮只产出 deficit-1 道（模拟部分题被 gate 拒的真实欠产）
+    backfill = _CountingBackfill(lambda d, r: [_q(f"bf{r}_{i}") for i in range(max(d - 1, 0))])
+    final_path = tmp_path / "accepted_questions_final.json"
+    await run_adversarial_rounds(
+        [_q("q0")],
+        agent=agent,
+        vlm=object(),
+        store=store,
+        trees={},
+        config=AdversarialFilterConfig(adversarial_max_rounds=3),
+        final_path=final_path,
+        target=99,  # 永远达不到 → 靠 max_rounds 终止，不因欠产崩溃或死循环
+        backfill=backfill,
+        session_id="s",
+    )
+    assert backfill.calls == 2  # round0/round1 各补一次；round2 达上限 break
+    ids = {d["question_id"] for d in json.loads(final_path.read_text(encoding="utf-8"))}
+    assert "q0" in ids and any(x.startswith("bf0_") for x in ids)  # 实得欠产题已并入
+    store.close()