Deliver BAT-004: broker execution + KIS adapter + durable handoff

Implement REQ-011~015 (dcy-003): the order-execution layer on top of the
BAT-002 slot-core daemon, connecting intents to real orders.
- application: BrokerPort (submit/poll_fill/cancel) + ExecutionService
  (claim -> submit -> poll -> transition -> rollback -> reconcile)
- adapters/broker: PaperBroker (deterministic async double) and KISBroker
  (KIS Open API: token, order-cash, inquire-daily-ccld, cancel; VTS sandbox
  tr_ids; live account gated behind allow_live)
- persistence: option-A execution queue (find_pending_for_dispatch FOR
  UPDATE SKIP LOCKED, mark_dispatched idempotency guard, clear_dispatch)
- runtime: background execution loop in the daemon lifespan + startup
  reconcile; config selects paper|kis

Verification (real KIS VTS 모의투자 + PostgreSQL): 92 passed, ruff clean,
domain import sweep shows zero broker/web/db deps, buy->holding /
sell->closed / reject->idle, idempotent dispatch (exactly one order),
reconcile after crash creates no duplicate order, KIS sandbox token+submit
round-trip, and a daemon E2E through the background loop. Align the four
baseline docs. BAT-004 -> release-candidate; REQ-011~015 -> Implemented.

KIS live-account go-live, partial-fill accrual, option-B outbox, connection
pooling, and the safety floor remain deferred to follow-up Discoveries.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

trex_core/adapters/broker/paper.py

@@ -0,0 +1,84 @@
+"""Paper/stub broker — deterministic async double (REQ-011, dcy-003 OQ-2).
+
+Follows the same submit -> poll contract as the real KIS adapter (no
+synchronous shortcut), but lets tests program WHEN/whether fills happen:
+immediate, after N polls, partial, or reject. This exercises the same
+execution code path that production (KIS) takes.
+"""
+from __future__ import annotations
+
+import threading
+from typing import Optional
+
+from trex_core.application.broker_port import FillStatus, OrderAck, OrderRequest
+
+
+class _Order:
+    def __init__(self, oid: str, req: OrderRequest) -> None:
+        self.oid = oid
+        self.side = req.side
+        self.symbol = req.symbol
+        self.qty = req.qty
+        self.price = float(req.limit_price) if req.limit_price is not None else 1000.0
+        self.polls = 0
+        self.filled = 0
+        self.cancelled = False
+
+
+class PaperBroker:
+    """Deterministic async paper broker.
+
+    - fill_after_polls: number of poll_fill calls before fills begin (0 => fills on first poll)
+    - qty_per_poll: filled quantity per poll once filling (None => fill remaining at once)
+    - reject_symbols: symbols whose orders are rejected on first poll
+    """
+
+    def __init__(
+        self,
+        *,
+        fill_after_polls: int = 0,
+        qty_per_poll: Optional[int] = None,
+        reject_symbols: Optional[set[str]] = None,
+    ) -> None:
+        self._fill_after = fill_after_polls
+        self._qty_per_poll = qty_per_poll
+        self._reject = reject_symbols or set()
+        self._orders: dict[str, _Order] = {}
+        self._seq = 0
+        self._lock = threading.Lock()
+
+    def name(self) -> str:
+        return "paper"
+
+    def submit_order(self, req: OrderRequest) -> OrderAck:
+        with self._lock:
+            self._seq += 1
+            oid = f"PAPER-{self._seq:06d}"
+            self._orders[oid] = _Order(oid, req)
+        return OrderAck(accepted=True, broker_order_id=oid)
+
+    def poll_fill(self, broker_order_id: str, *, side: str, symbol: str) -> FillStatus:
+        with self._lock:
+            o = self._orders.get(broker_order_id)
+            if o is None:
+                return FillStatus(state="unknown")
+            if o.cancelled:
+                return FillStatus(state="cancelled")
+            o.polls += 1
+            if symbol in self._reject:
+                return FillStatus(state="rejected", raw={"reason": "paper_reject"})
+            if o.polls <= self._fill_after:
+                return FillStatus(state="accepted", filled_qty=o.filled, avg_price=o.price)
+            step = self._qty_per_poll if self._qty_per_poll is not None else (o.qty - o.filled)
+            o.filled = min(o.qty, o.filled + step)
+            if o.filled >= o.qty:
+                return FillStatus(state="filled", filled_qty=o.filled, avg_price=o.price)
+            return FillStatus(state="partially_filled", filled_qty=o.filled, avg_price=o.price)
+
+    def cancel_order(self, broker_order_id: str, *, side: str, symbol: str, qty: int) -> bool:
+        with self._lock:
+            o = self._orders.get(broker_order_id)
+            if o is None or o.filled >= o.qty:
+                return False
+            o.cancelled = True
+            return True