Ensure that pre-vote messages are binary compatible with pre-pre-vote messages

[cjen1-msft]

The idea is that rather than using a field in the message to denote whether a message is for pre-vote or not, use the RaftMsgType to denote this.

To minimise the diff relative to the original code, this PR just adds new pre-vote versions of the raft_request_vote and raft_request_vote_response messages.

This means that the pre-vote variants can reuse the existing code, while there are not 'official' RequestPreVote struct, we just update the type in the RequestVote's header for pre-votes messages.

(I'll open a separate PR to address the snagging of docs etc for raft.h)

[Copilot]

Pull Request Overview

This PR refactors the Raft consensus protocol implementation to separate pre-vote and regular vote message types, moving from a field-based differentiation to distinct message types. This improves type safety and clarifies the distinction between pre-vote and regular vote operations.

• Introduced separate RequestPreVote and RequestPreVoteResponse message types alongside existing RequestVote and RequestVoteResponse
• Added corresponding enum values raft_request_pre_vote and raft_request_pre_vote_response to RaftMsgType
• Removed the election_type field from RequestVote and RequestVoteResponse structs, as the message type itself now determines whether it's a pre-vote or regular vote

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/consensus/aft/raft_types.h	Adds new RequestPreVote and RequestPreVoteResponse types, removes election_type field from vote request/response structs, and adds formatter for RaftMsgType enum
src/consensus/aft/raft.h	Updates message handling logic to use separate functions for pre-vote vs regular vote, adds recv/send handlers for new pre-vote message types
src/consensus/aft/test/driver.h	Adds logging support for new pre-vote message types and updates log messages to include message type
tla/consensus/Traceccfraft.tla	Updates trace validation to distinguish pre-vote from regular vote based on message type rather than election_type field
doc/architecture/raft_tla.rst	Minor grammar correction (validate → validating)

Comments suppressed due to low confidence (1)

src/consensus/aft/test/driver.h:533

• Incorrect type casting for raft_request_pre_vote_response. When the message type is raft_request_pre_vote_response, the code casts to RequestVoteResponse*, but it should cast to RequestPreVoteResponse* instead. These are different types with different RaftHeader base classes.

The case should be split into two separate cases:

• One for raft_request_vote_response that casts to RequestVoteResponse*
• One for raft_request_pre_vote_response that casts to RequestPreVoteResponse* and calls the appropriate overload of log_msg_details

      case (aft::RaftMsgType::raft_request_vote_response):
      case (aft::RaftMsgType::raft_request_pre_vote_response):
      {
        auto rvr = *(aft::RequestVoteResponse*)data;
        packet = rvr;
        log_msg_details(node_id, tgt_node_id, rvr, dropped);
        break;