Epic: Protocol completeness

[anorth]

This is a tracking issue for tasks required to reach core GPBFT protocol completeness. Lotus integration, finality certificates, and most testing are to be tracked in other epics.

Tasks

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1. Settle representation of voting power, truncation of native power #33
   blocked design-question +2
   
2. Use delayed power table to validate or drop messages from future instances #151
   4 of 4
   gossipbft +1
   
3. GPBFT instance should drop spammable messages from future rounds #240
   gossipbft +1
   
4. Skip to future rounds when justified by an incoming message #241
   gossipbft +1
   
5. Short-cut timeout in PREAPRE, COMMIT when justified by received messages #242
   1 of 2
   gossipbft +1
   
6. Rebroadcast last round messages when stuck at step longer than timeout #243
   gossipbft +1
   
7. Provide API for host to force progress from finality certificates #245
   +0
   
8. Implement basic denial-of-service resistence #12
   9 of 9
   Component +1
   
9. Unit tests for pieces of the GossipPBFT implementation #9
   16 of 16
   gossipbft testing +2
   
10. Review external audit and ensure all issues addressed in code #255
    +0
    
11. When to start an f3 instance #173
    design-question gossipbft +2
    
12. Final GPBFT protocol alignment with FIP #244
    6 of 6
    FIP gossipbft +2
    
13. Head input chain offset #175
    design-question +1
    

[jennijuju]

@anorth i added #12 here lmk if thats not right