feat(FN-5444): add merge handoff test coverage for task worktree

Adds test coverage for merge queue and heartbeat handoff interactions (FN-5444), including source metadata expectations in heartbeat executor tests, merge handoff coverage gaps, and reuse scenarios in the merger worktree integration tests.

Fusion-Task-Id: FN-5444

Fusion-Task-Lineage: 45e1b43f-8ae3-46ba-a5ee-25e8c661e753

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>
Fusion-Task-Id: FN-5444

packages/engine/src/__tests__/heartbeat-executor.test.ts

@@ -3182,6 +3182,10 @@ describe("executeHeartbeat", () => {
           sourceType: "agent_heartbeat",
           sourceAgentId: "agent-001",
           sourceRunId: "run-001",
+          sourceParentTaskId: "FN-001",
+          sourceMetadata: expect.objectContaining({
+            contentFingerprint: expect.any(String),
+          }),
         }),
       }), expect.objectContaining({ settings: { autoSummarizeTitles: false } }));
     });

packages/engine/src/__tests__/merger-integration-worktree.test.ts

@@ -653,12 +653,12 @@ describe("acquireReuseHandoff", () => {
     });
   });
 
-  it("refuses when no merge queue lease can be acquired", async () => {
+  it("FN-5444: no-lease refusal carries queue-head diagnostics and nulls when head is absent", async () => {
     const store = createStore();
-    store.acquireMergeQueueLease.mockReturnValue(null);
+    store.acquireMergeQueueLease.mockReturnValue({ taskId: "FN-5329" });
     store.peekMergeQueueHead.mockReturnValue({ taskId: "FN-5329", leasedBy: "merger-reuse-handoff", column: "todo" });
 
-    const refusal = await expectRefusal(
+    const refusalWithHead = await expectRefusal(
       acquireReuseHandoff({
         task: await store.getTask("FN-5279"),
         store,
@@ -667,11 +667,32 @@ describe("acquireReuseHandoff", () => {
         worktreePath: "/tmp/task-worktree",
       }),
       "lease-handoff-failed",
-      "target-not-queued",
+      "no-lease",
     );
-    expect(refusal.payload).toMatchObject({
+    expect(refusalWithHead.payload).toMatchObject({
       taskId: "FN-5279",
       worktreePath: "/tmp/task-worktree",
+      acquiredTaskId: "FN-5329",
+      queueHeadTaskId: "FN-5329",
+      queueHeadLeasedBy: "merger-reuse-handoff",
+    });
+
+    store.acquireMergeQueueLease.mockReturnValue({ taskId: "FN-5329" });
+    store.peekMergeQueueHead.mockReturnValue(null);
+    const refusalWithoutHead = await expectRefusal(
+      acquireReuseHandoff({
+        task: await store.getTask("FN-5279"),
+        store,
+        projectRoot: "/tmp/project-root",
+        settings: {} as any,
+        worktreePath: "/tmp/task-worktree",
+      }),
+      "lease-handoff-failed",
+      "no-lease",
+    );
+    expect(refusalWithoutHead.payload).toMatchObject({
+      queueHeadTaskId: null,
+      queueHeadLeasedBy: null,
     });
   });
 

packages/engine/src/__tests__/reliability-interactions/merge-reuse-task-worktree.test.ts

@@ -424,6 +424,44 @@ describe("FN-5279 reliability interactions: merge reuse task worktree", () => {
     }
   }, 60_000);
 
+  it.skipIf(!hasGit)("FN-5444: moving task out of in-review during live lease preserves row until release cleanup", async () => {
+    const { fixture, store, task } = await setupReuseHandoff({
+      taskId: "FN-5444-RI-COLUMN-EXIT-LIVE-LEASE",
+      fileName: "packages/engine/src/fn-5444-ri-column-exit.ts",
+      fileContent: "export const exitLease = true;\n",
+      commitMessage: "feat: add FN-5444 column exit lease coverage",
+      skipWorktreeAdd: true,
+      worktreeOverride: null,
+    });
+
+    try {
+      const lease = store.acquireMergeQueueLease("merger-reuse-handoff", {
+        targetTaskId: task.id,
+        leaseDurationMs: 60_000,
+        now: "2099-05-19T00:00:10.000Z",
+      });
+      expect(lease?.taskId).toBe(task.id);
+
+      await store.moveTask(task.id, "todo");
+      expect(store.peekMergeQueue().some((entry) => entry.taskId === task.id)).toBe(true);
+
+      const staleLeaseAudit = store.getRunAuditEvents({ taskId: task.id, mutationType: "mergeQueue:stale-lease-on-column-exit" });
+      expect(staleLeaseAudit).toHaveLength(1);
+      expect(staleLeaseAudit[0].metadata).toMatchObject({
+        taskId: task.id,
+        previousColumn: "in-review",
+        nextColumn: "todo",
+        leasedBy: "merger-reuse-handoff",
+      });
+      expect(typeof staleLeaseAudit[0].metadata?.leaseExpiresAt).toBe("string");
+
+      store.releaseMergeQueueLease(task.id, "merger-reuse-handoff", { kind: "success" });
+      expect(store.peekMergeQueue().some((entry) => entry.taskId === task.id)).toBe(false);
+    } finally {
+      await fixture.cleanup();
+    }
+  }, 60_000);
+
   it.skipIf(!hasGit)("already-landed branch auto-finalizes from the reused worktree path", async () => {
     const { fixture, rootDir, store, task, branch } = await setupReuseHandoff({
       taskId: "FN-5279-RI-ALREADY-LANDED",

packages/engine/src/merger.ts

@@ -899,7 +899,7 @@ export function packageNamesForFiles(rootDir: string, files: string[]): string[]
  *
  * @internal Exported for testing only.
  */
-export function deriveScopedPnpmTestCommand(rootDir: string, baseBranch: string): string | null {
+export function deriveScopedPnpmTestCommand(rootDir: string, baseBranch: string, branch: string): string | null {
   // 1. Read and parse pnpm-workspace.yaml
   const workspacePath = join(rootDir, "pnpm-workspace.yaml");
   let workspaceContent: string;
@@ -988,7 +988,7 @@ export function inferDefaultTestCommand(
     if (existsSync(join(rootDir, "pnpm-workspace.yaml"))) {
       if (baseBranch?.trim() && branch?.trim()) {
         try {
-          const scoped = deriveScopedPnpmTestCommand(rootDir, baseBranch.trim());
+          const scoped = deriveScopedPnpmTestCommand(rootDir, baseBranch.trim(), branch.trim());
           if (scoped) {
             mergerLog.log(
               `Scoped inferred test command to changed packages: ${scoped}`,