miner: add OpenTelemetry tracing spans to block building

Add tracing instrumentation to the payload building pipeline so operators
can identify where time is spent during block construction. This adds four
spans:

  - miner.buildPayload   (root span per build iteration)
  - miner.prepareWork    (header + state setup)
  - miner.fillTransactions (transaction selection + execution)
  - miner.finalizeAndAssemble (block finalization)

The root span is created via StartRootSpan since the background build
goroutine has no parent RPC context. Context is threaded through
generateWork → prepareWork/fillTransactions to enable child spans.

This complements the existing RPC-level tracing (jsonrpc.engine/getPayloadV*
server spans with rpc.encodeJSONResponse children) by providing visibility
into the block building phase itself.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/telemetry/telemetry.go

@@ -88,6 +88,13 @@ func StartServerSpan(ctx context.Context, tracer trace.Tracer, rpc RPCInfo, othe
 	return ctx, end
 }
 
+// StartRootSpan creates a SpanKind=INTERNAL root span that does not require
+// a parent span in the context. Use this for background operations that are
+// not triggered by an incoming RPC request.
+func StartRootSpan(spanName string, attributes ...Attribute) (context.Context, trace.Span, func(*error)) {
+	return startSpan(context.Background(), otel.Tracer(""), trace.SpanKindInternal, spanName, attributes...)
+}
+
 // startSpan creates a span with the given kind.
 func startSpan(ctx context.Context, tracer trace.Tracer, kind trace.SpanKind, spanName string, attributes ...Attribute) (context.Context, trace.Span, func(*error)) {
 	ctx, span := tracer.Start(ctx, spanName, trace.WithSpanKind(kind))

miner/miner.go

@@ -18,6 +18,7 @@
 package miner
 
 import (
+	"context"
 	"fmt"
 	"math/big"
 	"sync"
@@ -156,7 +157,7 @@ func (miner *Miner) getPending() *newPayloadResult {
 	if miner.chainConfig.IsShanghai(new(big.Int).Add(header.Number, big.NewInt(1)), timestamp) {
 		withdrawal = []*types.Withdrawal{}
 	}
-	ret := miner.generateWork(&generateParams{
+	ret := miner.generateWork(context.Background(), &generateParams{
 		timestamp:   timestamp,
 		forceTime:   false,
 		parentHash:  header.Hash(),

miner/payload_building.go

@@ -17,6 +17,7 @@
 package miner
 
 import (
+	"context"
 	"crypto/sha256"
 	"encoding/binary"
 	"math/big"
@@ -28,6 +29,7 @@ import (
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/stateless"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/telemetry"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
@@ -225,7 +227,7 @@ func (miner *Miner) buildPayload(args *BuildPayloadArgs, witness bool) (*Payload
 		slotNum:     args.SlotNum,
 		noTxs:       true,
 	}
-	empty := miner.generateWork(emptyParams, witness)
+	empty := miner.generateWork(context.Background(), emptyParams, witness)
 	if empty.err != nil {
 		return nil, empty.err
 	}
@@ -261,11 +263,17 @@ func (miner *Miner) buildPayload(args *BuildPayloadArgs, witness bool) (*Payload
 			select {
 			case <-timer.C:
 				start := time.Now()
-				r := miner.generateWork(fullParams, witness)
+				ctx, _, spanEnd := telemetry.StartRootSpan("miner.buildPayload",
+					telemetry.Int64Attribute("block.number", int64(args.Timestamp)),
+					telemetry.StringAttribute("payload.id", args.Id().String()),
+				)
+				r := miner.generateWork(ctx, fullParams, witness)
 				if r.err == nil {
 					payload.update(r, time.Since(start))
+					spanEnd(nil)
 				} else {
 					log.Info("Error while generating work", "id", payload.id, "err", r.err)
+					spanEnd(&r.err)
 				}
 				timer.Reset(max(0, miner.config.Recommit-time.Since(start)))
 			case <-payload.stop:
@@ -296,7 +304,7 @@ func (miner *Miner) BuildTestingPayload(args *BuildPayloadArgs, transactions []*
 		overrideExtraData: extraData,
 		overrideTxs:       transactions,
 	}
-	res := miner.generateWork(fullParams, false)
+	res := miner.generateWork(context.Background(), fullParams, false)
 	if res.err != nil {
 		return nil, res.err
 	}

miner/worker.go

@@ -17,6 +17,7 @@
 package miner
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"math/big"
@@ -32,6 +33,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/txpool"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/internal/telemetry"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/holiman/uint256"
@@ -120,8 +122,8 @@ type generateParams struct {
 }
 
 // generateWork generates a sealing block based on the given parameters.
-func (miner *Miner) generateWork(genParam *generateParams, witness bool) *newPayloadResult {
-	work, err := miner.prepareWork(genParam, witness)
+func (miner *Miner) generateWork(ctx context.Context, genParam *generateParams, witness bool) *newPayloadResult {
+	work, err := miner.prepareWork(ctx, genParam, witness)
 	if err != nil {
 		return &newPayloadResult{err: err}
 	}
@@ -157,7 +159,7 @@ func (miner *Miner) generateWork(genParam *generateParams, witness bool) *newPay
 			})
 			defer timer.Stop()
 
-			err := miner.fillTransactions(interrupt, work)
+			err := miner.fillTransactions(ctx, interrupt, work)
 			if errors.Is(err, errBlockInterruptedByTimeout) {
 				log.Warn("Block building is interrupted", "allowance", common.PrettyDuration(miner.config.Recommit))
 			}
@@ -192,10 +194,16 @@ func (miner *Miner) generateWork(genParam *generateParams, witness bool) *newPay
 		work.header.RequestsHash = &reqHash
 	}
 
+	var finalizeErr error
+	_, _, spanEnd := telemetry.StartSpan(ctx, "miner.finalizeAndAssemble")
 	block, err := miner.engine.FinalizeAndAssemble(miner.chain, work.header, work.state, &body, work.receipts)
 	if err != nil {
+		finalizeErr = err
+		spanEnd(&finalizeErr)
 		return &newPayloadResult{err: err}
 	}
+	spanEnd(&finalizeErr)
+
 	return &newPayloadResult{
 		block:    block,
 		fees:     totalFees(block, work.receipts),
@@ -210,7 +218,10 @@ func (miner *Miner) generateWork(genParam *generateParams, witness bool) *newPay
 // prepareWork constructs the sealing task according to the given parameters,
 // either based on the last chain head or specified parent. In this function
 // the pending transactions are not filled yet, only the empty task returned.
-func (miner *Miner) prepareWork(genParams *generateParams, witness bool) (*environment, error) {
+func (miner *Miner) prepareWork(ctx context.Context, genParams *generateParams, witness bool) (_ *environment, err error) {
+	_, _, spanEnd := telemetry.StartSpan(ctx, "miner.prepareWork")
+	defer spanEnd(&err)
+
 	miner.confMu.RLock()
 	defer miner.confMu.RUnlock()
 
@@ -502,7 +513,10 @@ func (miner *Miner) commitTransactions(env *environment, plainTxs, blobTxs *tran
 // fillTransactions retrieves the pending transactions from the txpool and fills them
 // into the given sealing block. The transaction selection and ordering strategy can
 // be customized with the plugin in the future.
-func (miner *Miner) fillTransactions(interrupt *atomic.Int32, env *environment) error {
+func (miner *Miner) fillTransactions(ctx context.Context, interrupt *atomic.Int32, env *environment) (err error) {
+	_, _, spanEnd := telemetry.StartSpan(ctx, "miner.fillTransactions")
+	defer spanEnd(&err)
+
 	miner.confMu.RLock()
 	tip := miner.config.GasPrice
 	prio := miner.prio