Adds one paragraph to the SSTORE refund for slot restoration section clarifying that the state gas refund is scoped to the executing frame and does not propagate to the parent on revert or exceptional halt.

Motivation

The current text describes where and when the refund is applied (immediately at the X to 0 SSTORE, directly to state_gas_reservoir) but is silent on what happens if the frame that performed the X to 0 SSTORE subsequently fails. Two interpretations are consistent with the existing wording:

1. The credit to state_gas_reservoir is irrevocable once applied.
2. The credit is scoped to the frame and is undone on failure.

Only (2) is consistent with the EIP's own principle that state gas is only refunded when no state was actually grown, and with the rest of the document's treatment of reverted frames.

Under (1), a sub-call that performs 0 to X to 0 and then reverts leaves state_gas_reservoir inflated relative to its pre-call value, effectively converting parent gas_left into reservoir state gas via a reverted frame. This contradicts the net-state-growth-is-zero justification and is a consensus-split risk between clients that read the existing text differently.

EELS Spec & Tests

ethereum/execution-specs#2698