Kaggle Notebooks Interactive Session Timeout vs. Background Save Version: In-Memory State Persistence Boundary

Kaggle Notebooks enforce a documented 12-hour limit on interactive sessions, while background Save & Run All executions may continue for up to 90 hours independent of the browser. A manual Stop terminates the virtual machine immediately, discarding volatile memory. However, the precise compatibility boundary between an interactive session timeout, an inactivity-based GPU/TPU preemption, and a background run's failure mode remains unclear when a script holds large de-serialized objects in memory.

The uncertainty is whether the kernel's termination reason—user-initiated cancellation versus an automated inactivity timeout or resource de-allocation—affects what is flushed to persistent storage before the instance is reclaimed. If the execution mode changes mid-run, or if the browser session ends while a background process is active, the persistence guarantees for in-memory state are not explicitly documented.

Does an inactivity timeout during a background Save & Run All session preserve disk state differently than a manual Stop? Is there a deterministic point at which GPU/TPU preemption invalidates in-memory objects that were not explicitly checkpointed? How should long-running notebooks be structured to account for the transition from interactive execution to background execution without relying on volatile memory?