feat(FN-4813): complete Step 3 — add owning-node handoff policy

Fusion-Task-Id: FN-4813
Fusion-Task-Lineage: 846893a5-2afa-4817-8f64-8c444d2fd713

packages/engine/src/node-routing-policy.ts

@@ -1,4 +1,4 @@
-import type { NodeStatus, UnavailableNodePolicy } from "@fusion/core";
+import type { NodeStatus, OwningNodeHandoffPolicy, Task, UnavailableNodePolicy } from "@fusion/core";
 import type { EffectiveNode } from "./effective-node.js";
 
 export type PolicyDecision =
@@ -6,6 +6,11 @@ export type PolicyDecision =
   | { allowed: true; fallbackToLocal: true; reason: string }
   | { allowed: false; reason: string };
 
+export type HandoffDecision =
+  | { action: "park"; reason: string }
+  | { action: "reassign-local"; reason: string }
+  | { action: "reassign-any"; reason: string };
+
 const UNHEALTHY_STATUSES: ReadonlySet<NodeStatus> = new Set(["offline", "error", "connecting"]);
 
 export function applyUnavailableNodePolicy(params: {
@@ -40,3 +45,36 @@ export function applyUnavailableNodePolicy(params: {
     reason: `Node ${effectiveNode.nodeId} is ${nodeHealth}; policy is block`,
   };
 }
+
+export function decideOwningNodeHandoff(params: {
+  task: Task;
+  ownerNodeId: string;
+  ownerNodeHealth: NodeStatus | undefined;
+  localNodeId: string;
+  handoffPolicy: OwningNodeHandoffPolicy | undefined;
+}): HandoffDecision {
+  const { ownerNodeId, ownerNodeHealth, localNodeId, handoffPolicy } = params;
+  if (ownerNodeHealth === "online") {
+    return { action: "park", reason: "owner_recovered" };
+  }
+
+  if (ownerNodeId === localNodeId) {
+    return { action: "reassign-local", reason: "owner_local_recover" };
+  }
+
+  if (handoffPolicy === "block") {
+    return { action: "park", reason: "handoff_blocked_by_policy" };
+  }
+
+  if (handoffPolicy === "reassign-any-healthy") {
+    return {
+      action: "reassign-any",
+      reason: `owner_${ownerNodeHealth ?? "unknown"}_any_healthy_eligible`,
+    };
+  }
+
+  return {
+    action: "reassign-local",
+    reason: `owner_${ownerNodeHealth ?? "unknown"}_local_takes_over`,
+  };
+}