> For the complete documentation index, see [llms.txt](https://docs.usegimbal.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.usegimbal.app/risk/sequencer.md).

# When the sequencer stops

Robinhood Chain runs on one sequencer. This page lists the ways it can fail and the four mechanisms that let a Gimbal position be repaid, topped up or cancelled through each one.

A loan has to stay steerable when the chain beneath it goes quiet. Robinhood Chain runs as an Arbitrum Nitro rollup with a single sequencer, operated by Robinhood, which is normal for an L2 of its age. It brings a known list of failure modes, and the protocol is built to work through each of them.

## Four defences

### The uptime feed and the one-hour grace period

`PriceSentinel` consults Chainlink's L2 Sequencer Uptime Feed, set with `setSequencerFeed`. The feed answers 0 while the sequencer is running and 1 while it is down, and `startedAt` marks when the current state began. For `sequencerGrace` seconds after the sequencer returns, one hour in the deployed loan parameters, every quote carries the `sequencerGrace` flag. While it is set no auction can open and no loan can originate, because a price nobody could trade against during the outage is not yet one anyone should be liquidated on. Borrowers get the hour to add collateral or repay. A sequencer that is still down counts as grace, as does an uptime round with no usable start time, so a broken feed errs toward blocking liquidations.

### Force inclusion through the delayed inbox

Every state-changing function can be reached through the delayed inbox Arbitrum keeps on Ethereum. Should the sequencer leave such a transaction out for 24 hours, anyone can force it in. So:

* a sequencer that censors cannot keep a borrower from calling `repay`,
* a sequencer that censors cannot keep a lender from calling `cancel` or `cancelWord` on an offer nonce,
* a borrower who sees an outage coming can queue `addCollateral` from L1 before it starts.

With the grace period alongside it, the delayed inbox is a path people can plan around rather than a footnote.

### Time from the clock, never from the block

On an Arbitrum-stack chain `block.number` reports a value tied to L1 rather than the L2's own height. The contracts therefore read `block.timestamp` for accrual, expiry and auction timing, and never read `block.number` at all. Should a genuine L2 block height ever be required, the route is `ArbSys.arbBlockNumber()`; nothing in the current set needs it.

### Calldata kept small

Gas for the L1 data part of a transaction depends on how well the calldata compresses. Offer structs use tight packing, and 64-byte compact signatures are accepted wherever a signer can produce one. An `originate` call carrying twenty offers stays affordable.

## What can go wrong

| Failure                           | Effect on a user                                                                                                                                    |
| --------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------- |
| The sequencer is down             | No transaction reaches the L2 before it returns. The stock market does not stop trading in the meantime.                                            |
| The sequencer censors             | Particular transactions, a repayment for instance, never get included.                                                                              |
| L1 finality is slow               | A withdrawal to Ethereum takes the standard 7 days. Loans on the L2 carry on unaffected.                                                            |
| The chain's configuration changes | A different DA mode, a new validator set, or the activation of Timeboost or BoLD could alter what the protocol assumes about ordering and finality. |

## Watching the configuration

Two questions depend on whether Timeboost (express-lane ordering) and BoLD (permissionless validation) are live on Robinhood Chain: which liquidator reaches an auction first, and how soon a force-included transaction can be treated as final. Gimbal follows both. If Timeboost goes live, the auction mechanics get a review to confirm the express lane cannot be used to front-run keepers as a matter of course, and any resulting change goes into the governance log. Current chain values are on [Network parameters](/robinhood-chain/parameters.md).


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