feat(conductor): add configurable HTTP body limit for large execution payloads

[zjg555543]

Problem

Sequencer fails to commit large blocks to Conductor with 413 Request Entity Too Large:

lvl=error msg="Engine failed temporarily, backing off sequencer"
err="failed to commit unsafe payload to conductor:
413 Request Entity Too Large: content length too large (9340888>5242880)"

Root Cause: Default HTTP body limit is 5MB, insufficient for blocks with 150+ transactions (9.3MB).

Call Stack & Evidence

Evidence Type	Location	Description
Entry Point	op-conductor/cmd/main.go:25	main() starts conductor
RPC Init	service.go:117	initRPCServer() called by init()
RPC Start	service.go:435	rpcServer.Start() starts service
go.mod Replace	go.mod	go-ethereum → okx/op-geth
Import Declaration	handler.go:12	import "github.com/ethereum/go-ethereum/rpc"
Call op-geth	handler.go:150	rpc.NewServer() creates op-geth Server
Set Limit	handler.go:155	srv.SetHTTPBodyLimit(b.httpBodyLimit)
op-geth Implementation	op-geth/rpc/server.go:96	SetHTTPBodyLimit() method
Validation Logic	op-geth/rpc/http.go:345	HTTP body size check

Execution Flow

conductor main (cmd/main.go:25)
    ↓
conductor.New() → init() → initRPCServer() (service.go:92,117)
    ↓
oprpc.NewServer(WithHTTPBodyLimit(64MB)) (service.go:278)
    ↓
handler.NewHandler() → AddRPC() (handler.go:58,150)
    ↓
rpc.NewServer() [via go.mod replace → op-geth/rpc]
    ↓
srv.SetHTTPBodyLimit(64MB) (handler.go:155)
    ↓
s.httpBodyLimit = 67108864 (op-geth/rpc/server.go:97)
    ↓
ServeHTTP() → validateRequest() (op-geth/rpc/http.go:310,341)
    ↓
if ContentLength > httpBodyLimit { return 413 } ✅ (http.go:345)

Dependency Chain

go.mod: github.com/ethereum/go-ethereum
          → replaced with github.com/okx/op-geth
             ↓
op-service/rpc imports "github.com/ethereum/go-ethereum/rpc"
             ↓
Actually uses op-geth/rpc due to replace directive
             ↓
SetHTTPBodyLimit() defined in op-geth/rpc/server.go:96
             ↓
Validation occurs in op-geth/rpc/http.go:345

Solution

Increase Conductor's HTTP body limit to 64MB by leveraging op-geth's SetHTTPBodyLimit() API.

Changes

1. Add WithHTTPBodyLimit() option in handler_options.go
2. Apply limit via srv.SetHTTPBodyLimit() in handler.go
3. Set 64MB for Conductor in service.go:278
4. Add error logging with payload size in sequencer.go

Configuration

# Flag, default is 5 MB
- --rpc.http-body-limit-mb=64

[opgitgovernance]

This pr has been automatically marked as stale and will be closed in 5 days if no updates