ckUNI’s Cycles Ceiling Was a Storage-Risk Boundary

NNS proposal 143958 targets a quiet but important failure mode in the ckUNI ledger: storage growth can become impossible because of a reserved-cycles ceiling, even when the canister still has cycles available.

The proposal would raise the reserved_cycles_limit for canister ilzky-ayaaa-aaaar-qahha-cai from 5 trillion cycles—the documented default—to 1 quintillion cycles. The setting caps a secondary balance used for future resource payments. According to the ICP canister-settings documentation, storage reservations move cycles from a canister’s main balance into this reserved balance when storage usage on a subnet exceeds 750 GiB.

That distinction is the proposal’s central engineering point. The limit is not a funding allocation and does not itself spend cycles. It is a ceiling on how much of the canister’s existing balance may be moved into reserve. The underlying IC implementation also defines 5 trillion cycles as the default reserved-balance limit when a canister has no custom value configured. In practical terms, raising the setting gives the ledger more room to grow under storage pressure; it does not provide the ledger with new economic resources.

The supplied proposal argues that the default can be too small on the 34-node fiduciary subnet. At the cited worst-case reservation rate, 5 trillion cycles would cover only about 20 MiB of growth. This figure comes from the proposal material and was not independently reproduced here, so it should be read as the proposer’s capacity estimate rather than a general network-wide constant.

The governance path is also notable. The ckUNI ledger is managed by the ledger suite orchestrator, but the NNS root canister is described in the proposal as a co-controller. That is why the setting is changed directly through an NNS proposal rather than routed through the orchestrator. The proposal links an earlier ledger-suite-orchestrator decision, but this item is specifically about the ledger canister’s resource setting.

For Chain Fusion infrastructure, the lesson is operational: balance monitoring and growth-limit monitoring are separate tasks. A ledger can remain funded while still approaching a hard reservation boundary. Raising the limit removes that particular bottleneck, while leaving the actual cycles balance—and therefore the canister’s responsibility to remain funded—unchanged.

The dashboard page returned an internal error during live verification, so this article does not assert the proposal’s vote status or outcome. The article therefore describes the requested change and its documented mechanism, not a completed governance result.

Related proposals on the same desk addressed reserved-cycles limits for the ckWBTC index and ledger canisters; those items are context, not evidence that proposal 143958 was executed.