Proposals for second iteration of the HFC

[amesgen]

The most intricate parts of the HFC related to how time/era transitions are performed have been largely unmodified since they were first introduced¹. Recently, investigating IntersectMBO/cardano-ledger#3491 lead us to scrutinize these aspects, resulting in improving our understanding of the status quo and giving rise to potential improvements.

As the aforementioned issue has been resolved in #366 (albeit in a relatively ad-hoc fashion), there is no immediate need to make any large HFC changes. Instead, the purpose of this issue is to give an overview over the HFC-related changes that came out of this effort.

Documentation

• There is now a HWW entry for the status quo of the HFC.
• Document HFC #921

HFC behavior

• [FEAT] - Generalize how the HFC handles era transitions #345
• Remove TriggerHardForkAtEpoch #416
• HFC: require that every era contains at least one safe zone worth of slots #417
• Reconsider HFC requirement that ticking cannot make a transition become known #413 (likely part of implementing alternatives to block counting)
• "Block counting" related:
  • Cardano SingleEraBlock instances should stop counting blocks after the nonce snapshot #385
  • Reconsider counting blocks in the HFC #389 (might supersede the previous point)
• Reconsider requiring era transition knowledge to not be subject to rollback ("double stability") #419

Footnotes

1. This is largely due to the fact that they did their job well, with one notable exception: https://github.com/input-output-hk/ouroboros-network/pull/3754 ↩