feat(FN-2614): merge fusion/fn-2614 (auto-resolved)

- feat(FN-2614): complete Step 4 — configure vitest test isolation setup
- test(FN-2614): complete Step 3 — add isolation companion test
- feat(FN-2614): complete Step 2 — add test home isolation setup

packages/pi-claude-cli/src/__tests__/setup-test-isolation.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from "vitest";
+import { homedir, tmpdir } from "node:os";
+import { join } from "node:path";
+
+const TEMP_HOME_PREFIX = "fn-test-home-";
+
+describe("test isolation setup", () => {
+  it("overrides process.env.HOME to a temp directory", () => {
+    const home = process.env.HOME;
+
+    expect(home).toBeDefined();
+    expect(home).toContain(tmpdir());
+    expect(home).toContain(TEMP_HOME_PREFIX);
+  });
+
+  it("resolves homedir() to the temp HOME", () => {
+    const home = homedir();
+
+    expect(home).toContain(tmpdir());
+    expect(home).toContain(TEMP_HOME_PREFIX);
+  });
+
+  it("resolves ~/.pi/agent/AGENTS.md under the temp HOME", () => {
+    const agentsPath = join(homedir(), ".pi", "agent", "AGENTS.md");
+
+    expect(agentsPath).toContain(tmpdir());
+    expect(agentsPath).toContain(TEMP_HOME_PREFIX);
+    expect(agentsPath).toMatch(/fn-test-home-.*[\\/]\.pi[\\/]agent[\\/]AGENTS\.md$/);
+  });
+});

packages/pi-claude-cli/src/__tests__/setup-test-isolation.ts

@@ -0,0 +1,6 @@
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+const tempHome = mkdtempSync(join(tmpdir(), "fn-test-home-"));
+process.env.HOME = tempHome;