feat: add SyncCallback for progress events

Chain now supports SetSyncCallback(localHeight, remoteHeight, bps).
Wired into BlockchainService to emit EventSyncProgress events.
Enables live sync progress in explorer, status dashboard, and stream.

Per RFC.pubsub.md: blockchain.sync.progress event.

Co-Authored-By: Charon <charon@lethean.io>

chain/chain.go

@@ -18,6 +18,7 @@ import (
 type Chain struct {
 	store         *store.Store
 	blockCallback BlockCallback
+	syncCallback  SyncCallback
 }
 
 // New creates a Chain backed by the given store.
@@ -69,9 +70,19 @@ func (c *Chain) Snapshot() (uint64, *types.Block, *BlockMeta) {
 // BlockCallback is called after a block is successfully stored.
 type BlockCallback func(height uint64, hash string, aliasName string)
 
+// SyncCallback is called periodically during chain sync with progress info.
+type SyncCallback func(localHeight, remoteHeight uint64, blocksPerSecond float64)
+
 // SetBlockCallback sets a function called after each block is stored.
 //
 //	c.SetBlockCallback(func(height uint64, hash string, alias string) { ... })
 func (c *Chain) SetBlockCallback(cb BlockCallback) {
 	c.blockCallback = cb
 }
+
+// SetSyncCallback sets a function called during sync progress.
+//
+//	c.SetSyncCallback(func(local, remote uint64, bps float64) { ... })
+func (c *Chain) SetSyncCallback(cb SyncCallback) {
+	c.syncCallback = cb
+}

service.go

@@ -91,6 +91,15 @@ func (s *BlockchainService) start() core.Result {
 		}
 	})
 
+	// Wire sync progress events
+	s.chain.SetSyncCallback(func(localHeight, remoteHeight uint64, blocksPerSecond float64) {
+		s.events.Emit(Event{Type: EventSyncProgress, Height: localHeight, Data: map[string]interface{}{
+			"local_height":    localHeight,
+			"remote_height":   remoteHeight,
+			"blocks_per_sec":  blocksPerSecond,
+		}})
+	})
+
 	cfg, forks := resolveConfig(s.opts.Testnet, &s.opts.Seed)
 
 	// Start background sync.