v4.4.0 — the pin moves to Go 1.27.1

Synced to baseline v4.4.0 (rules commit ce86f13): go.mod says go 1.27; the handler-test harness runs on httptest.NewTestServer; drainAndClose is gone; verify.sh gates the go line against the pin's major (79 gates, exit 0); make ci green under go1.27.1. Dependencies updated under the pin.