hook.env was applied after the server-provided SIGNALTTY_SOCKET /
EVENT / PLUGIN_DIR / PLUGIN_NAME bindings, so a mistaken or malicious
manifest could redirect hooks at another socket or forge event
identity. Apply hook.env first and force the reserved bindings after;
custom keys remain additive.

Co-authored-by: Grok Bot <grok-bot@users.noreply.github.com>
Co-authored-by: Lucenx9 <185146821+Lucenx9@users.noreply.github.com>