Plumbline is an open-source operational stability layer for the Filecoin CalibrationNet, providing a deliberately stable Storage Provider test target, a public dual-asset faucet for repeatable developer funding, and continuous network monitoring to keep integration environments reliable. It also delivers end-to-end network-version upgrade validation with publicly verifiable results, reducing ecosystem risk and accelerating builder and Storage Provider testing cycles. The project expands this foundation with self-serve onboarding and a read-only builder API to standardize access to calibration funding and health signals across downstream tooling.