perf(cmpp): add durable inbound fast path

gateway/internal/inbound/submit.go

@@ -4,6 +4,7 @@ import (
 	"cmpp-platform/gateway/internal/metrics"
 	"context"
 	"crypto/md5"
+	"crypto/sha256"
 	"errors"
 	"fmt"
 	cmpp "github.com/bigwhite/gocmpp"
@@ -19,6 +20,7 @@ import (
 // one internal message mapping per destination while CMPP receives one response.
 
 type submitRequest struct {
+	RequestID          string                      `json:"requestId,omitempty"`
 	Account            string                      `json:"account"`
 	PhoneNumber        string                      `json:"phoneNumber,omitempty"`
 	PhoneNumbers       []string                    `json:"phoneNumbers,omitempty"`
@@ -117,6 +119,7 @@ func (s Server) handleSubmit(response *cmpp.Response, packet *cmpp.Packet, logge
 	releaseSubmitBarrier := beginDownstreamSubmitBarrier(packet.Conn)
 	apiStartedAt := time.Now()
 	result, err := s.submit(remote, submitRequest{
+		RequestID:          inboundSubmitRequestID(session.connectionID, req.sequenceID, phones, content, req.srcID, longMessage),
 		Account:            account,
 		PhoneNumber:        phone,
 		PhoneNumbers:       phones,
@@ -222,6 +225,14 @@ func (s Server) handleSubmit(response *cmpp.Response, packet *cmpp.Packet, logge
 	return false, nil
 }
 
+func inboundSubmitRequestID(connectionID string, sequenceID uint32, phones []string, content string, srcID string, longMessage *inboundLongMessageFragment) string {
+	// The key is stable for an API retry of the same packet but scoped to the authenticated
+	// connection, so a later client session may intentionally reuse the CMPP Sequence_Id.
+	payload := fmt.Sprintf("%s\x00%d\x00%s\x00%s\x00%s\x00%v", connectionID, sequenceID, strings.Join(phones, ","), strings.TrimSpace(srcID), content, longMessage)
+	digest := sha256.Sum256([]byte(payload))
+	return fmt.Sprintf("cmpp-inbound:%x", digest[:])
+}
+
 func observeInboundSubmitResponse(handlerStartedAt time.Time, responseReadyAt time.Time, accepted bool, next func(error)) func(error) {
 	return func(sendErr error) {
 		metrics.ObserveInboundStage("response_write", sendErr == nil, time.Since(responseReadyAt))