feat(config): BAT-028 M1 — max_active_slots per-instance TOML (dcy-020/REQ-060)

자산 중심 모드 게이트 + M 값. DaemonInstanceConfig/DaemonConfig 에
max_active_slots: Optional[int] 추가, from_toml 파싱(>0 검증), from_config 전파.
미설정(None) → legacy pool 모드. additive — 전체 375 passed, ruff clean.

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

trex_core/runtime/config.py

@@ -143,6 +143,10 @@ class DaemonInstanceConfig:
     # Optional — absent keys fall back to KST / midnight defaults.
     trading_timezone: str = "Asia/Seoul"
     daily_preallocation_time: str = "00:00"
+    # dcy-020 / REQ-060 (BAT-028): max concurrent active (holding) slots, M.
+    # Presence is the asset-centric mode gate: set -> universe reconcile + FCFS/M
+    # admission; absent -> legacy pool model (preallocation + find_allocatable).
+    max_active_slots: Optional[int] = None
 
     @staticmethod
     def from_toml(path: str) -> "DaemonInstanceConfig":
@@ -155,11 +159,18 @@ class DaemonInstanceConfig:
             raise RuntimeError(
                 f"instance TOML missing required 'instance_key': {path}"
             )
+        raw_max = data.get("max_active_slots")
+        max_active = int(raw_max) if raw_max is not None else None
+        if max_active is not None and max_active <= 0:
+            raise RuntimeError(
+                f"instance TOML 'max_active_slots' must be > 0, got {raw_max}: {path}"
+            )
         return DaemonInstanceConfig(
             instance_key=str(instance_key),
             portfolio_hub_token=str(data.get("portfolio_hub_token") or ""),
             trading_timezone=str(data.get("trading_timezone") or "Asia/Seoul"),
             daily_preallocation_time=str(data.get("daily_preallocation_time") or "00:00"),
+            max_active_slots=max_active,
         )
 
 
@@ -172,6 +183,9 @@ class DaemonConfig:
     # BAT-013 / REQ-049: instance identity for multi-instance queue naming.
     # "default" keeps legacy literal queue names (backward-compat).
     instance_key: str = "default"
+    # dcy-020 / REQ-060 (BAT-028): M (max concurrent active slots) + asset-centric
+    # mode gate. None -> legacy pool model.
+    max_active_slots: Optional[int] = None
     kis: Optional[KISConfig] = None
     # REQ-011: paper broker tuning (only consulted when broker == 'paper').
     paper: PaperBrokerConfig = PaperBrokerConfig()
@@ -316,4 +330,5 @@ class DaemonConfig:
             portfolio_hub=pf,
             trading_timezone=inst.trading_timezone,
             daily_preallocation_time=inst.daily_preallocation_time,
+            max_active_slots=inst.max_active_slots,
         )