Overload Raptor Chunk Header Epoch

[michael-yxchen]

A full node may join new RaptorCast groups from the same validator while it's syncing or stuck. In such cases, it may rebroadcast to an expired group because its local round hasn't advanced, and expired groups are not garbage-collected. As a result, many full nodes end up receiving unsolicited Raptor chunks from groups they no longer belong to.

The root cause is that the node selects the rebroadcast group based on its local round. This PR resolves the issue by overloading the epoch field in the Raptor chunk header setting it to the round number for secondary raptorcast. This allows syncing or stuck full nodes to use the round number to identify and service the correct group

The base branch was changed.

[Copilot]

Pull Request Overview

This PR addresses an issue where full nodes receive unsolicited Raptor chunks from expired groups during network synchronization. The solution overloads the epoch field in Raptor chunk headers to carry round numbers for secondary RaptorCast (validator-to-fullnode), enabling nodes to correctly identify and service groups based on actual round numbers rather than their potentially stale local state.

Key Changes:

• Introduced GroupId enum to distinguish between Primary (epoch-based) and Secondary (round-based) RaptorCast groups
• Replaced epoch-only tracking with group-specific identification in chunk headers and validation logic
• Updated group lookup and validation to use round numbers for secondary RaptorCast
• Removed epoch-based pruning from decoder cache in favor of timestamp-based expiration

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
monad-types/src/lib.rs	Removed unused From<Epoch> trait implementation
monad-state/src/consensus.rs	Added round field to PublishToFullNodes command
monad-router-multi/src/lib.rs	Updated router to propagate round field in full node publishing
monad-raptorcast/src/udp.rs	Introduced GroupId enum and updated message parsing/validation
monad-raptorcast/src/util.rs	Changed fullnode group storage from heap to BTreeMap keyed by round
monad-raptorcast/src/packet/*.rs	Updated packet building to use GroupId instead of raw epoch
monad-raptorcast/src/decoding.rs	Removed epoch-based cache pruning logic
monad-raptorcast/src/raptorcast_secondary/mod.rs	Updated secondary RaptorCast to use round-based group IDs
monad-executor-glue/src/lib.rs	Added round field to PublishToFullNodes enum variant
monad-consensus-state/src/command.rs	Extended consensus commands to include round numbers
test files	Updated test cases to use new GroupId type

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