test(daemon): isolate HOME for the package test binary (#252)

Many pkg/daemon tests construct New(Config{}) with an empty IdentityPath,
so the daemon resolves managed-engine state (~/.pilot/managed_<netID>.json),
the hostname cache, and the network snapshot under os.UserHomeDir() — the
real home. Run in parallel (within the package and across the packages
go test ./... runs concurrently on a shared CI runner) those tests race on
the same ~/.pilot files, flaking on macOS (the snapshot / hostname-cache /
managed-engine tests, which pass in isolation).

Add a TestMain that points HOME (and USERPROFILE) at a throwaway dir before
any test runs, making the package hermetic. Verified: tests no longer touch
the real ~/.pilot; suite green; repeated concurrent ./pkg/... runs clean.

Co-authored-by: Teodor Calin <teodor@vulturelabs.io>

Author: TeoSlayer

pkg/daemon/zz_testmain_test.go

@@ -0,0 +1,36 @@
+package daemon
+
+import (
+	"os"
+	"testing"
+)
+
+// TestMain isolates HOME for the entire package test binary.
+//
+// Many tests here construct a daemon with New(Config{}) (empty
+// IdentityPath). Such a daemon resolves its on-disk state — managed-engine
+// files (~/.pilot/managed_<netID>.json), the hostname cache, the network
+// snapshot — under os.UserHomeDir(). Without isolation those tests read and
+// write the *real* home concurrently: both within this package's parallel
+// tests and across the packages that `go test ./...` runs in parallel on a
+// shared CI runner. That races on the same files and flakes (observed
+// reddening macOS CI on the snapshot / hostname-cache / managed-engine
+// tests, which pass in isolation).
+//
+// Pointing HOME (and USERPROFILE, for os.UserHomeDir on Windows) at a
+// throwaway directory before any test runs makes every test in this
+// package hermetic. Tests that set their own HOME via t.Setenv still work —
+// they override and restore relative to this base.
+func TestMain(m *testing.M) {
+	tmp, err := os.MkdirTemp("", "pilot-daemon-test-home-")
+	if err != nil {
+		panic("daemon test: create temp HOME: " + err.Error())
+	}
+	_ = os.Setenv("HOME", tmp)
+	_ = os.Setenv("USERPROFILE", tmp)
+
+	code := m.Run()
+
+	_ = os.RemoveAll(tmp)
+	os.Exit(code)
+}