fix(init): report the real invoke ID for runtime fault events

Resolve the fault request ID in the events API: prefer an explicit ID,
then the current invoke ID so a mid-invocation runtime crash reports the
actual request, and only synthesize a UUID as a fallback for init-phase
faults where no invocation has been dispatched yet. Previously the
supervisor always passed a random UUID, masking the real invoke ID.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: joe4dev

cmd/localstack/events.go

@@ -8,6 +8,7 @@ import (
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/interop"
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/rapidcore/standalone/telemetry"
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lsapi"
+	"github.com/google/uuid"
 )
 
 // LocalStackEventsAPI intercepts fault events and forwards them to LocalStack as error status callbacks.
@@ -29,11 +30,17 @@ func (ev *LocalStackEventsAPI) SendFault(data interop.FaultData) error {
 	_ = ev.StandaloneEventsAPI.SendFault(data)
 
 	requestID := string(data.RequestID)
-	if data.RequestID == "" {
+	if requestID == "" {
 		ev.mu.RLock()
 		requestID = ev.requestID
 		ev.mu.RUnlock()
 	}
+	if requestID == "" {
+		// No invocation is active during the init phase (LocalStack only dispatches an invoke
+		// after the runtime reports ready), so synthesize an ID to preserve AWS's
+		// "RequestId: <uuid> Error: ..." message format.
+		requestID = uuid.NewString()
+	}
 
 	resp := lsapi.ErrorResponse{
 		ErrorMessage: fmt.Sprintf("RequestId: %s Error: %s", requestID, data.ErrorMessage),

cmd/localstack/supervisor.go

@@ -11,7 +11,6 @@ import (
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/interop"
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/supervisor"
 	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/supervisor/model"
-	"github.com/google/uuid"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -77,8 +76,10 @@ func (ls *LocalStackSupervisor) loop(ctx context.Context) {
 				log.Debugf("Runtime process signalled: %d", *termination.Signo)
 			}
 
+			// RequestID is left empty so the events API can resolve it: it uses the current
+			// invoke ID for a mid-invocation crash and synthesizes a placeholder for init-phase
+			// faults, where no invocation has been dispatched yet.
 			faultData := interop.FaultData{
-				RequestID:    interop.RequestID(uuid.NewString()),
 				ErrorMessage: errors.New("Runtime exited without providing a reason"),
 				ErrorType:    fatalerror.RuntimeExit,
 			}