Worker sync protocol uses bulk SyncBatch instead of per-author Advertise/Request/Response

[intendednull]

Problem

The worker sync actor (crates/worker/src/actors/sync.rs:68-82) uses WorkerRequest::Sync { server_id, heads } with bulk WorkerResponse::SyncBatch { events } responses. This does not match the spec's per-author sync protocol.

Spec requires:

pub enum SyncMessage {
    /// "Here's what I have." Sent on connect and periodically.
    Advertise(HeadsSummary),
    /// "I need events from these authors after these seq numbers."
    Request(Vec<AuthorRequest>),
    /// "Here are events you're missing."
    Response(Vec<Event>),
}

pub struct AuthorRequest {
    pub author: EndpointId,
    pub after_seq: u64,
}

Current implementation:

• Sync broadcasts a single WorkerRequest::Sync with heads
• Response is a bulk SyncBatch of all events, not per-author
• No Advertise message for proactive head exchange
• No AuthorRequest for targeted per-author fetching

Impact

• Redundant data transfer — bulk batches include events the requester already has
• No per-author granularity — cannot request specific authors' missing events
• Doesn't support parallel fetching from different authors
• Mismatched with the client's sync protocol evolution (Migrate client SyncRequest to heads-based sync protocol #43)

Suggested fix

Implement the spec's three-phase sync:

1. Advertise: periodically broadcast HeadsSummary (already partially done via heads_summaries())
2. Request: compare received heads against local DAG, request missing per-author ranges
3. Response: send requested events in seq order per author

Location

• crates/worker/src/actors/sync.rs:68-82
• crates/worker/src/actors/state.rs:34-43 (response format)
• crates/common/src/worker_types.rs (WorkerRequest/WorkerResponse types)

References

• Spec: docs/specs/2026-04-01-per-author-merkle-dag-state-design.md (Section 3, Sync Protocol)
• Related: Migrate client SyncRequest to heads-based sync protocol #43 (client sync migration)
• Found during codebase audit against DAG spec