refactor(runtime): add run DDD boundary skeleton

backend/packages/harness/deerflow/runtime/runs/domain/policies.py

@@ -0,0 +1,50 @@
+"""Domain policies for run concurrency and cancellation."""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+from dataclasses import dataclass
+from enum import StrEnum
+
+from .model import Run
+from .value_objects import CancelAction, MultitaskStrategy, RunStatus
+
+
+class MultitaskDecision(StrEnum):
+    """Application-level decision produced by a multitask policy."""
+
+    allow = "allow"
+    reject = "reject"
+    cancel_existing = "cancel_existing"
+    enqueue = "enqueue"
+
+
+@dataclass(frozen=True)
+class MultitaskPolicy:
+    strategy: MultitaskStrategy = MultitaskStrategy.reject
+
+    def decide(self, active_runs: Sequence[Run]) -> MultitaskDecision:
+        inflight = [run for run in active_runs if run.status in (RunStatus.pending, RunStatus.running)]
+        if not inflight:
+            return MultitaskDecision.allow
+        if self.strategy == MultitaskStrategy.reject:
+            return MultitaskDecision.reject
+        if self.strategy in (MultitaskStrategy.interrupt, MultitaskStrategy.rollback):
+            return MultitaskDecision.cancel_existing
+        return MultitaskDecision.enqueue
+
+
+@dataclass(frozen=True)
+class CancelPolicy:
+    action: CancelAction = CancelAction.interrupt
+
+    @property
+    def rolls_back_checkpoint(self) -> bool:
+        return self.action == CancelAction.rollback
+
+
+__all__ = [
+    "CancelPolicy",
+    "MultitaskDecision",
+    "MultitaskPolicy",
+]