How can Gentoo's Portage FEATURES be used to cancel or time out builds gracefully?

The goal is to ensure that when a Portage build exceeds a desired duration or is interrupted by the user, the ebuild process stops cleanly and any temporary files or locks are removed without leaving the system in an inconsistent state.

Assuming Gentoo's Portage provides a FEATURES variable that can influence build‑time limits or cleanup actions, which specific flag governs timeout enforcement? How does Portage respond to a SIGINT during compilation, and what cleanup steps are performed automatically? Are there complementary mechanisms, such as wrapping the emerge command with a timeout utility, that integrate cleanly with Portage's transaction model?