test(FN-4715): complete Step 2 — add default invariant regressions

Fusion-Task-Id: FN-4715
Fusion-Task-Lineage: b1c3393f-2596-4b3f-a8fb-c9838bf6c985

packages/core/src/__tests__/settings-defaults.test.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+import { DEFAULT_GLOBAL_SETTINGS, DEFAULT_PROJECT_SETTINGS } from "../settings-schema.js";
+import { resolveWorktrunkSettings, validateWorktrunkSettings } from "../worktrunk-settings.js";
+
+describe("settings defaults invariants", () => {
+  it("keeps worktrunk default off in global and project defaults", () => {
+    expect(DEFAULT_GLOBAL_SETTINGS.worktrunk.enabled).toBe(false);
+    expect(DEFAULT_PROJECT_SETTINGS.worktrunk.enabled).toBe(false);
+  });
+
+  it("keeps project worktreesDir unset by default", () => {
+    expect(DEFAULT_PROJECT_SETTINGS.worktreesDir).toBeUndefined();
+  });
+
+  it("resolves worktrunk as disabled when both scopes are unset or empty", () => {
+    expect(resolveWorktrunkSettings(undefined, undefined).enabled).toBe(false);
+    expect(resolveWorktrunkSettings({}, {}).enabled).toBe(false);
+  });
+
+  it("preserves explicit false overrides for worktrunk enabled", () => {
+    expect(resolveWorktrunkSettings({ enabled: false }, undefined).enabled).toBe(false);
+    expect(resolveWorktrunkSettings(undefined, { enabled: false }).enabled).toBe(false);
+  });
+
+  it("does not implicitly enable worktrunk when validating undefined", () => {
+    expect(validateWorktrunkSettings(undefined)).toEqual({});
+  });
+});

packages/engine/src/__tests__/worktree-paths.test.ts

@@ -15,6 +15,10 @@ describe("worktree-paths", () => {
     expect(resolveWorktreesDir(rootDir, undefined)).toBe(join(rootDir, ".worktrees"));
   });
 
+  it("defaults to <rootDir>/.worktrees when settings object is present but worktreesDir is unset", () => {
+    expect(resolveWorktreesDir(rootDir, {} as any)).toBe(join(rootDir, ".worktrees"));
+  });
+
   it("supports absolute path", () => {
     expect(resolveWorktreesDir(rootDir, { worktreesDir: "/var/tmp/fn-worktrees" } as any)).toBe("/var/tmp/fn-worktrees");
   });