test(FN-4976): add reliability backstop for self-owned session-registry deadlock

Fusion-Task-Id: FN-4976
Fusion-Task-Lineage: b7d6e778-f6b1-4529-b04b-81352a11ddad

packages/engine/src/__tests__/reliability-interactions/stale-self-owned-session-registry.test.ts

@@ -0,0 +1,75 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import "../executor-test-helpers.js";
+import { TaskExecutor } from "../../executor.js";
+import { activeSessionRegistry } from "../../active-session-registry.js";
+import { createMockStore, mockedExistsSync, resetExecutorMocks } from "../executor-test-helpers.js";
+import * as worktreePoolModule from "../../worktree-pool.js";
+
+const ROOT = "/tmp/test";
+const PATH = "/tmp/test/.worktrees/fn-4976";
+const BRANCH = "fusion/fn-4976";
+const TASK_ID = "FN-4976";
+
+describe("FN-4976: stale self-owned activeSessionRegistry deadlock backstop", () => {
+  beforeEach(() => {
+    resetExecutorMocks();
+    activeSessionRegistry.unregisterPath(PATH);
+    mockedExistsSync.mockImplementation((input: Parameters<typeof mockedExistsSync>[0]) => input === PATH);
+  });
+
+  afterEach(() => {
+    activeSessionRegistry.unregisterPath(PATH);
+  });
+
+  it("FN-4976 clears same-task stale activeSessionRegistry entry and cleanup succeeds", async () => {
+    const store = createMockStore();
+    store.listTasks.mockResolvedValue([]);
+    activeSessionRegistry.registerPath(PATH, { taskId: TASK_ID, kind: "executor", ownerKey: TASK_ID });
+
+    const executor = new TaskExecutor(store, ROOT);
+    const removeSpy = vi.spyOn(worktreePoolModule, "removeWorktree").mockResolvedValue(undefined);
+    const result = await (executor as any).cleanupConflictingWorktree(PATH, BRANCH, TASK_ID);
+
+    expect(result).toBe(true);
+    expect(removeSpy).toHaveBeenCalled();
+    expect(activeSessionRegistry.lookupByPath(PATH)).toBeNull();
+    expect(store.logEntry).toHaveBeenCalledWith(
+      TASK_ID,
+      "Cleared stale self-owned activeSessionRegistry entry",
+      PATH,
+    );
+  });
+
+  it("FN-4976 does not clear foreign-owned activeSessionRegistry entry and FN-4811 refusal still fires", async () => {
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, ROOT);
+    (executor as any).activeWorktrees.set("FN-OTHER", PATH);
+    store.listTasks.mockResolvedValue([]);
+    activeSessionRegistry.registerPath(PATH, { taskId: "FN-OTHER", kind: "executor", ownerKey: "FN-OTHER" });
+
+    const result = await (executor as any).cleanupConflictingWorktree(PATH, BRANCH, TASK_ID);
+
+    expect(result).toBe(false);
+    expect(activeSessionRegistry.lookupByPath(PATH)?.taskId).toBe("FN-OTHER");
+    const messages = store.logEntry.mock.calls.map((call: any[]) => String(call[1] ?? ""));
+    expect(messages.some((m: string) => m.includes("Refused to remove conflicting worktree"))).toBe(true);
+    expect(messages.some((m: string) => m.includes("Cleared stale self-owned activeSessionRegistry entry"))).toBe(false);
+  });
+
+  it("FN-4976 leaves behavior unchanged when no stale entry exists", async () => {
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, ROOT);
+    store.listTasks.mockResolvedValue([]);
+    const unregisterSpy = vi.spyOn(activeSessionRegistry, "unregisterPath");
+    const removeSpy = vi.spyOn(worktreePoolModule, "removeWorktree").mockResolvedValue(undefined);
+
+    const result = await (executor as any).cleanupConflictingWorktree(PATH, BRANCH, TASK_ID);
+
+    expect(removeSpy).toHaveBeenCalled();
+
+    expect(result).toBe(true);
+    expect(unregisterSpy).not.toHaveBeenCalledWith(PATH);
+    const messages = store.logEntry.mock.calls.map((call: any[]) => String(call[1] ?? ""));
+    expect(messages.some((m: string) => m.includes("Cleared stale self-owned activeSessionRegistry entry"))).toBe(false);
+  });
+});