feat(chain): add BlockCallback fired after every block stored

Chain.SetBlockCallback(func(height, hash, aliasName)) enables
event-driven architecture — the EventBus subscribes to block
storage and emits events without coupling chain to events.

Callback fires in processBlockBlobs after PutBlock succeeds.
Includes alias name if the block contains an alias registration.

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

chain/chain.go

@@ -16,7 +16,8 @@ import (
 // Chain manages blockchain storage and indexing.
 // Usage: var value chain.Chain
 type Chain struct {
-	store *store.Store
+	store         *store.Store
+	blockCallback BlockCallback
 }
 
 // New creates a Chain backed by the given store.
@@ -64,3 +65,13 @@ func (c *Chain) Snapshot() (uint64, *types.Block, *BlockMeta) {
 	}
 	return height, blk, meta
 }
+
+// BlockCallback is called after a block is successfully stored.
+type BlockCallback func(height uint64, hash string, aliasName string)
+
+// 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
+}

chain/sync.go

@@ -280,7 +280,20 @@ func (c *Chain) processBlockBlobs(blockBlob []byte, txBlobs [][]byte,
 		CumulativeDiff: cumulDiff,
 		GeneratedCoins: 0, // not available from wire; RPC path passes via bd.BaseReward
 	}
-	return c.PutBlock(&blk, meta)
+	if err := c.PutBlock(&blk, meta); err != nil {
+		return err
+	}
+
+	// Fire block callback if registered.
+	if c.blockCallback != nil {
+		aliasName := ""
+		if alias := ExtractAliasFromExtra(blk.MinerTx.Extra); alias != nil {
+			aliasName = alias.Name
+		}
+		c.blockCallback(height, blockHash.String(), aliasName)
+	}
+
+	return nil
 }
 
 // indexOutputs adds each output of a transaction to the global output index.