Why Plugin Systems Slowly Break Down: The Case for Strict Boundaries

Plugin systems often degrade not through sudden failure but through gradual accommodation, as each small expansion of plugin access seems reasonable in isolation. Over time, plugins gain access to internal state, lifecycle hooks, and mutable globals, effectively becoming a second system running alongside the core. This erosion of boundaries turns internal details into accidental contracts, making the core dependent on its own extensions. A second problem arises when responsibility for enforcing system invariants is shared informally, leading to order-dependent, undocumented behavior that is difficult to debug. A third failure mode, capability leakage, occurs when plugins are given broad execution power rather than narrow interfaces, stripping the core of predictability and forcing it to defensively account for plugin interference throughout.