fix(init): emit START after suppressed init to match AWS log ordering

The synthetic START line was written eagerly when LocalStack dispatched /invoke,
i.e. before the suppressed init re-runs the function's static code. AWS emits
START upon the Invoke event reaching the runtime, which rapidcore sequences after
any inline (suppressed) init (doInvoke -> sendInvokeStartLogEvent).

Emit START from a minimal LocalStackEventsAPI.SendInvokeStart override (riding
rapidcore's correctly-placed invoke-start event) and drop the eager write in the
/invoke handler. Correct for warm, cold, and suppressed-init invocations; fixes
test_lambda_timeout_init_phase against the unmodified AWS snapshot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: joe4dev

cmd/localstack/custom_interop.go

@@ -137,8 +137,8 @@ func NewCustomInteropServer(lsOpts *LsOpts, adapter *LocalStackAdapter, delegate
 				}
 
 				invokeResp := &standalone.ResponseWriterProxy{}
-				functionVersion := GetEnvOrDie("AWS_LAMBDA_FUNCTION_VERSION") // default $LATEST
-				_, _ = fmt.Fprintf(logCollector, "START RequestId: %s Version: %s\n", invokeR.InvokeId, functionVersion)
+				// The synthetic START line is emitted via LocalStackEventsAPI.SendInvokeStart so it
+				// lands after any inline (suppressed) init, matching AWS — see events.go.
 
 				initDuration := ""
 				if !server.warmStart && !server.initTimedOut.Load() {

cmd/localstack/events.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/interop"
+	"github.com/aws/aws-lambda-runtime-interface-emulator/internal/lambda/rapidcore/standalone/telemetry"
+)
+
+// LocalStackEventsAPI rides rapidcore's invoke lifecycle events to emit the synthetic START
+// log line at the AWS-faithful point. rapidcore calls SendInvokeStart after any inline
+// (suppressed) init and before the runtime handles the invocation (see doInvoke in
+// internal/lambda/rapid/handlers.go), so emitting START here — rather than eagerly when
+// LocalStack dispatches /invoke — places it after a re-run init's logs, matching AWS.
+type LocalStackEventsAPI struct {
+	*telemetry.StandaloneEventsAPI
+	logCollector *LogCollector
+}
+
+func NewLocalStackEventsAPI(logCollector *LogCollector) *LocalStackEventsAPI {
+	return &LocalStackEventsAPI{
+		StandaloneEventsAPI: new(telemetry.StandaloneEventsAPI),
+		logCollector:        logCollector,
+	}
+}
+
+func (e *LocalStackEventsAPI) SendInvokeStart(data interop.InvokeStartData) error {
+	_, _ = fmt.Fprintf(e.logCollector, "START RequestId: %s Version: %s\n", data.RequestID, data.Version)
+	return e.StandaloneEventsAPI.SendInvokeStart(data)
+}

cmd/localstack/main.go

@@ -196,6 +196,10 @@ func main() {
 		RuntimeId:        lsOpts.RuntimeId,
 	}
 
+	// Events API rides rapidcore's invoke lifecycle to emit the synthetic START log line after
+	// any inline (suppressed) init, matching AWS's ordering.
+	lsEventsAPI := NewLocalStackEventsAPI(logCollector)
+
 	// build sandbox
 	sandbox := rapidcore.
 		NewSandboxBuilder().
@@ -207,7 +211,8 @@ func main() {
 		SetExtensionsFlag(true).
 		SetInitCachingFlag(true).
 		SetLogsEgressAPI(localStackLogsEgressApi).
-		SetTracer(tracer)
+		SetTracer(tracer).
+		SetEventsAPI(lsEventsAPI)
 
 	// Corresponds to the 'AWS_LAMBDA_RUNTIME_API' environment variable.
 	// We need to ensure the runtime server is up before the INIT phase,