fix: close broker uncertainty audit gaps

trex_core/domain/slot/__init__.py

@@ -11,11 +11,13 @@ Public API:
 - EXPECTED_SLOT_FIELDS: canonical `Slot` column contract (guarded by test_contract)
 - SlotService: main domain service (transit, sell, thresholds, capacity)
 - SlotRepository: abstract storage protocol
-- SlotTransitionError / SlotStateMismatchError / SlotNotFoundError: domain errors
+- SlotTransitionError / SlotStateMismatchError / SlotAdmissionRejectedError /
+  SlotNotFoundError: domain errors
 """
 from __future__ import annotations
 
 from trex_core.domain.slot.errors import (
+    SlotAdmissionRejectedError,
     SlotDomainError,
     SlotNotFoundError,
     SlotStateMismatchError,
@@ -42,6 +44,7 @@ __all__ = [
     "EXPECTED_SLOT_FIELDS",
     "SLOT_ADVISORY_LOCK_ID",
     "Slot",
+    "SlotAdmissionRejectedError",
     "SlotCapacity",
     "SlotDomainError",
     "SlotNotFoundError",

trex_core/domain/slot/errors.py

@@ -21,3 +21,11 @@ class SlotStateMismatchError(SlotDomainError):
     different state between read and write (race detection inside the
     transition function).
     """
+
+
+class SlotAdmissionRejectedError(SlotDomainError):
+    """Raised when an advisory-locked admission precondition rejects."""
+
+    def __init__(self, reason: str) -> None:
+        self.reason = reason
+        super().__init__(reason)

trex_core/domain/slot/in_memory_repository.py

@@ -224,6 +224,8 @@ class InMemorySlotRepository:
         slot_id: UUID,
         broker_order_id: str,
         state: str,
+        *,
+        only_if_unset: bool = False,
     ) -> bool:
         """Persist one cancel attempt iff the same order is still pending."""
         s = self._slots.get(slot_id)
@@ -231,6 +233,7 @@ class InMemorySlotRepository:
             s is None
             or s.broker_order_id != broker_order_id
             or s.status not in self._PENDING
+            or (only_if_unset and s.cancel_state is not None)
         ):
             return False
         now = datetime.now(tz=timezone.utc)

trex_core/domain/slot/service.py

@@ -15,10 +15,11 @@ from __future__ import annotations
 from dataclasses import replace
 from datetime import datetime, timezone
 from decimal import Decimal
-from typing import Any, Optional
+from typing import Any, Callable, Optional
 from uuid import UUID
 
 from trex_core.domain.slot.errors import (
+    SlotAdmissionRejectedError,
     SlotNotFoundError,
     SlotStateMismatchError,
     SlotTransitionError,
@@ -87,6 +88,7 @@ class SlotService:
         slippage_pct: Optional[float] = None,
         venue: Optional[str] = None,
         extra: Optional[dict[str, Any]] = None,
+        precondition: Optional[Callable[[Slot], Optional[str]]] = None,
     ) -> Slot:
         """Transition slot from one state to another atomically.
 
@@ -116,6 +118,10 @@ class SlotService:
                     f"slot {slot_id} current state {slot.status.value} "
                     f"!= requested from_state {from_state.value}"
                 )
+            if precondition is not None:
+                rejection_reason = precondition(slot)
+                if rejection_reason is not None:
+                    raise SlotAdmissionRejectedError(rejection_reason)
 
             updated = self._apply_transition_fields(
                 slot,