What are the hidden invariants LINQ assumes but never enforces?

LINQ assumes immutability of source during enumeration, stable provider translation, and deterministic execution order.

LINQ relies on several implicit assumptions: source collections do not mutate during iteration, deferred execution will not be invalidated, and providers will consistently translate expressions. None of these are strictly enforced by the framework. Violating these assumptions leads to subtle bugs like inconsistent results, runtime exceptions, or nondeterministic behavior.