Deal Observer research: how to handle deal expiration/extension/slashing

[bajtos]

Finish the research on building a DB of active FIL+ deals by observing actor events. Write a design spec for the Deal Observer implementation.

We need to handle the following cases:

• A new verified deal is activated
• A deal reaches its expiration time
• A deal is slashed
• A deal is extended

We also want to maintain allocator-client map to link deals to allocators.

Resources:

• Research notes:
  https://docs.google.com/document/d/1YvFYYUwP6VibKyTeHLd89mrkB1S5sVjq9ydFCGbBfrw

• Deals can be extended:
  https://docs.filswan.com/swan-storage-market/core-modules/extend-datacap-terms-service
  https://lotus.filecoin.io/lotus/manage/claim-extension/

We need at least the following data for each deal:

• miner_id
• client_id
• piece_cid
• piece_size

[bajtos]

More resources:

• Filecoin non-CC Sector Lifecycle
• Early sector terminations are complicated: Exposure of Sector Status Method to Smart contracts from Builtin Miner Actor filecoin-project/FIPs#1108 (comment)