feat(FN-4606): complete Step 2 — add worktree path resolver

Ref: Runfusion/Fusion#321
Fusion-Task-Id: FN-4606
Fusion-Task-Lineage: 94b23f37-944e-4bcd-bfa1-67d0a8c0a267

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

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import { homedir } from "node:os";
+import { join, resolve } from "node:path";
+import {
+  isInsideConfiguredWorktreesDir,
+  resolveTaskWorktreePath,
+  resolveWorktreesDir,
+} from "../worktree-paths.js";
+
+describe("worktree-paths", () => {
+  const rootDir = "/tmp/repo-name";
+
+  it("defaults to <rootDir>/.worktrees when unset", () => {
+    expect(resolveWorktreesDir(rootDir, undefined)).toBe(join(rootDir, ".worktrees"));
+  });
+
+  it("supports absolute path", () => {
+    expect(resolveWorktreesDir(rootDir, { worktreesDir: "/var/tmp/fn-worktrees" } as any)).toBe("/var/tmp/fn-worktrees");
+  });
+
+  it("supports ~ expansion", () => {
+    expect(resolveWorktreesDir(rootDir, { worktreesDir: "~/.fn-worktrees" } as any)).toBe(join(homedir(), ".fn-worktrees"));
+  });
+
+  it("supports relative path with {repo}", () => {
+    expect(resolveWorktreesDir(rootDir, { worktreesDir: "../{repo}.worktrees" } as any)).toBe(resolve(rootDir, "../repo-name.worktrees"));
+  });
+
+  it("supports {repo} substitution mid-path", () => {
+    expect(resolveWorktreesDir(rootDir, { worktreesDir: "~/.fn/{repo}/trees" } as any)).toBe(join(homedir(), ".fn/repo-name/trees"));
+  });
+
+  it("builds task worktree path under configured dir", () => {
+    expect(resolveTaskWorktreePath(rootDir, { worktreesDir: "../{repo}.worktrees" } as any, "fn-123")).toBe(
+      resolve(rootDir, "../repo-name.worktrees/fn-123"),
+    );
+  });
+
+  it("detects paths inside and outside configured dir", () => {
+    const dir = resolveWorktreesDir(rootDir, { worktreesDir: "../{repo}.worktrees" } as any);
+    expect(isInsideConfiguredWorktreesDir(rootDir, { worktreesDir: "../{repo}.worktrees" } as any, join(dir, "fn-1"))).toBe(true);
+    expect(isInsideConfiguredWorktreesDir(rootDir, { worktreesDir: "../{repo}.worktrees" } as any, join(rootDir, "elsewhere", "fn-1"))).toBe(false);
+    expect(isInsideConfiguredWorktreesDir(rootDir, { worktreesDir: "../{repo}.worktrees" } as any, dir)).toBe(false);
+  });
+
+  it("legacy .worktrees default still works for containment checks", () => {
+    expect(isInsideConfiguredWorktreesDir(rootDir, undefined, join(rootDir, ".worktrees", "fn-1"))).toBe(true);
+    expect(isInsideConfiguredWorktreesDir(rootDir, undefined, join(rootDir, "fn-1"))).toBe(false);
+  });
+});