feat(slot): dcy-021 포지션 사이징 — 보유 슬롯 증액·부분 매도 (BAT-031)

자산 영구 슬롯(dcy-020)의 수량 가변 전제 위에 보유 포지션 수량 조정 구현.
명령형 계약(전략이 cash+quantity 로 qty+price 계산), core 는 실행 substrate,
수량 정본 = 브로커 잔고 재동기화로 "주문 수량 vs 보유 수량" 충돌 해소(별도 필드 없음).

- state.py: holding→pending_buy 전이 추가(증액) → 13 transitions (REQ-057)
- service.py: PENDING_SELL 진입 qty=caller as-is(None=전량 sentinel, 값=부분 주문) (REQ-062)
- intents.py: 증액 admission(holding 슬롯 매수=increase, M 캡 미적용), SellIntent.qty 부분 매도 (REQ-061)
- execution.py: _balance_map; 매도 dispatch=브로커잔고(전량)/min(주문,잔고)(부분);
  매수 체결 avg_price 가중평균+브로커 정본 resync; 매도 체결 잔고>0→holding/0→inactive;
  증액 롤백 holding 복귀 (REQ-066/062)
- messaging_handlers.py: sell payload qty 파싱(부분 매도)
- baseline 4문서(data-model/runtime-flows/interface-contract/project-structure) 정합 (REQ-067)

검증: 단위 378 / 통합(PG+RabbitMQ) 422 passed, ruff clean. run-the-app 사이징 e2e:
매수 10@1000 → 증액 +5@1200 → 15@1066.67(가중평균) → 부분 매도 6 → 9@1066.67(cost basis) → 전량→inactive.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/application/test_execution.py

@@ -77,19 +77,75 @@ def test_sell_lifecycle_returns_to_inactive():
     assert slot.qty is None and slot.portfolio_id == "PF-1"
 
 
-def test_sell_qty_is_broker_balance_not_slot_mirror():
-    """dcy-020/REQ-062 (D3): sell dispatch quantity = broker hldg_qty even when
-    the slot mirror qty is stale."""
+def test_full_sell_qty_is_broker_balance():
+    """dcy-020/REQ-062 (D3): full sell (slot.qty None) dispatches the broker
+    hldg_qty — independent of any stale mirror."""
     broker = PaperBroker(fill_after_polls=0)
     repo, svc, intents, execution = _wire(broker)
     sid = _buy(intents, qty=10).slot_id
     execution.run_once()  # holding, broker balance = 10
-    # corrupt the mirror: slot says 7, broker says 10
-    svc.transit_slot(sid, SlotState.HOLDING, SlotState.PENDING_SELL,
-                     reason="r", actor="t", qty=7.0)
-    execution.run_once()  # dispatch sell with broker qty
+    svc.sell(sid, actor="t", reason="full")  # qty=None -> sell all
+    execution.run_once()
     sell_orders = [o for o in broker._orders.values() if o.side == "sell"]
     assert len(sell_orders) == 1 and sell_orders[0].qty == 10
+    assert repo.fetch_slot(sid).status is SlotState.INACTIVE  # full exit
+
+
+def test_partial_sell_qty_is_min_intent_broker():
+    """dcy-021/REQ-062 (D4): partial sell dispatches min(intent qty, broker);
+    remainder stays holding (broker-authoritative qty), cost basis preserved."""
+    broker = PaperBroker(fill_after_polls=0)
+    repo, svc, intents, execution = _wire(broker)
+    sid = _buy(intents, qty=10).slot_id
+    execution.run_once()  # holding 10 @ avg 1000
+    intents.submit_sell(SellIntent(intent_id="ps", slot_id=sid, qty=4))
+    execution.run_once()  # dispatch sell 4 + fill -> holding remainder 6
+    sell_orders = [o for o in broker._orders.values() if o.side == "sell"]
+    assert len(sell_orders) == 1 and sell_orders[0].qty == 4
+    slot = repo.fetch_slot(sid)
+    assert slot.status is SlotState.HOLDING and slot.qty == 6
+    assert slot.avg_price == 1000.0  # cost basis unchanged
+
+
+def test_partial_sell_caps_at_broker_balance():
+    """intent qty above the broker balance => full sell (min caps at balance)."""
+    broker = PaperBroker(fill_after_polls=0)
+    repo, svc, intents, execution = _wire(broker)
+    sid = _buy(intents, qty=10).slot_id
+    execution.run_once()  # holding 10
+    intents.submit_sell(SellIntent(intent_id="ps", slot_id=sid, qty=999))
+    execution.run_once()
+    sell_orders = [o for o in broker._orders.values() if o.side == "sell"]
+    assert sell_orders[0].qty == 10  # capped at balance
+    assert repo.fetch_slot(sid).status is SlotState.INACTIVE  # nothing left
+
+
+def test_increase_accumulates_qty_and_weights_avg_price():
+    """dcy-021/REQ-066: buy on a holding slot increases the position; held qty =
+    broker balance, avg_price = weighted average."""
+    broker = PaperBroker(fill_after_polls=0)
+    repo, svc, intents, execution = _wire(broker)
+    sid = _buy(intents, pid="PF-1").slot_id  # qty 10 @ 1000
+    execution.run_once()  # holding 10 @ 1000
+    assert repo.fetch_slot(sid).qty == 10 and repo.fetch_slot(sid).avg_price == 1000.0
+    # increase: same asset, +5 @ 1200 (buy on the holding slot)
+    d = intents.submit_buy(BuyIntent(intent_id="inc", slot_id=sid, qty=5, entry_price=1200))
+    assert d.status == "admitted"
+    assert repo.fetch_slot(sid).status is SlotState.PENDING_BUY
+    execution.run_once()  # fill increase -> holding 15, weighted avg
+    slot = repo.fetch_slot(sid)
+    assert slot.status is SlotState.HOLDING and slot.qty == 15
+    assert slot.avg_price == (10 * 1000 + 5 * 1200) / 15  # 1066.67
+
+
+def test_increase_does_not_consume_capacity():
+    """dcy-021: increasing an already-active asset is not blocked by M cap."""
+    repo, svc, intents, execution = _wire(PaperBroker(fill_after_polls=0), max_active_slots=1)
+    sid = _buy(intents, iid="b0", pid="PF-0").slot_id
+    execution.run_once()  # PF-0 holding (active=1=M)
+    # a NEW asset would be capacity_full, but an increase on PF-0 is allowed
+    d = intents.submit_buy(BuyIntent(intent_id="inc", slot_id=sid, qty=5, entry_price=1000))
+    assert d.status == "admitted"
 
 
 def test_sell_skipped_when_broker_flat():