feat(FN-4813): complete Step 2 — add distributed claim mutex tests

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

packages/core/src/__tests__/checkout-claim-mutex.test.ts

@@ -0,0 +1,74 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { mkdtempSync } from "node:fs";
+import { rm } from "node:fs/promises";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { AgentStore } from "../agent-store.js";
+import { TaskStore } from "../store.js";
+import { CheckoutConflictError } from "../types.js";
+
+function makeTmpDir(): string {
+  return mkdtempSync(join(tmpdir(), "fn-checkout-claim-test-"));
+}
+
+describe("checkout claim mutex", () => {
+  let rootDir: string;
+  let taskStore: TaskStore;
+  let agentStore: AgentStore;
+  let globalDir: string;
+  let taskId: string;
+  let agentA: string;
+  let agentB: string;
+
+  beforeEach(async () => {
+    rootDir = makeTmpDir();
+    globalDir = join(rootDir, ".fusion-global");
+    taskStore = new TaskStore(rootDir, globalDir, { inMemoryDb: true });
+    await taskStore.init();
+    agentStore = new AgentStore({ rootDir, inMemoryDb: true, taskStore });
+    await agentStore.init();
+
+    agentA = (await agentStore.createAgent({ name: "A", role: "executor" })).id;
+    agentB = (await agentStore.createAgent({ name: "B", role: "executor" })).id;
+    taskId = (await taskStore.createTask({ description: "claim me" })).id;
+  });
+
+  afterEach(async () => {
+    agentStore?.close();
+    taskStore?.close();
+    await rm(rootDir, { recursive: true, force: true, maxRetries: 5, retryDelay: 50 });
+  });
+
+  it("first claimant wins and epoch becomes 1", async () => {
+    const claimed = await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-1" });
+    expect(claimed.checkedOutBy).toBe(agentA);
+    expect(claimed.checkoutNodeId).toBe("node-a");
+    expect(claimed.checkoutLeaseEpoch).toBe(1);
+  });
+
+  it("different agent claim conflicts and preserves owner", async () => {
+    await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-1" });
+    await expect(agentStore.checkoutTask(agentB, taskId, { nodeId: "node-b", runId: "run-2" })).rejects.toBeInstanceOf(CheckoutConflictError);
+    const current = await taskStore.getTask(taskId);
+    expect(current?.checkedOutBy).toBe(agentA);
+    expect(current?.checkoutNodeId).toBe("node-a");
+  });
+
+  it("same agent on different node conflicts", async () => {
+    await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-1" });
+    await expect(agentStore.checkoutTask(agentA, taskId, { nodeId: "node-b", runId: "run-2", leaseEpoch: 1 })).rejects.toBeInstanceOf(CheckoutConflictError);
+  });
+
+  it("renewal with matching epoch succeeds and does not bump epoch", async () => {
+    await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-1" });
+    const renewed = await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-2", leaseEpoch: 1, renewedAt: "2026-05-16T00:00:00.000Z" });
+    expect(renewed.checkoutLeaseEpoch).toBe(1);
+    expect(renewed.checkoutRunId).toBe("run-2");
+    expect(renewed.checkoutLeaseRenewedAt).toBe("2026-05-16T00:00:00.000Z");
+  });
+
+  it("renewal with stale epoch conflicts", async () => {
+    await agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-1" });
+    await expect(agentStore.checkoutTask(agentA, taskId, { nodeId: "node-a", runId: "run-2", leaseEpoch: 0 })).rejects.toBeInstanceOf(CheckoutConflictError);
+  });
+});