fix: align envelope timestamp precision and hide codec helpers (#107 #109)

EnvelopeMetadataCodec encodes the envelope timestamp with
DateTimeInterface::RFC3339_EXTENDED (millisecond precision), matching the
EventLog row format, and its scope/trace/correlation/endpoint splitter
helpers are now private since they are only used internally.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: nficano

src/Internal/Json/EnvelopeMetadataCodec.php

@@ -35,7 +35,7 @@ public function envelopeToArray(Envelope $env): array
             'arcp' => $env->arcp,
             'id' => (string) $env->id,
             'type' => $env->type(),
-            'timestamp' => $env->timestamp->format('Y-m-d\\TH:i:s.up'),
+            'timestamp' => $env->timestamp->format(\DateTimeInterface::RFC3339_EXTENDED),
         ];
         if ($env->priority !== Priority::Normal) {
             $out['priority'] = $env->priority->value;
@@ -52,7 +52,7 @@ public function envelopeToArray(Envelope $env): array
     /**
      * @return array<string, string>
      */
-    public function scopeIdsToArray(Envelope $env): array
+    private function scopeIdsToArray(Envelope $env): array
     {
         $out = [];
         if ($env->sessionId instanceof SessionId) {
@@ -73,7 +73,7 @@ public function scopeIdsToArray(Envelope $env): array
     /**
      * @return array<string, string>
      */
-    public function traceIdsToArray(Envelope $env): array
+    private function traceIdsToArray(Envelope $env): array
     {
         $out = [];
         if ($env->traceId instanceof TraceId) {
@@ -91,7 +91,7 @@ public function traceIdsToArray(Envelope $env): array
     /**
      * @return array<string, string>
      */
-    public function correlationIdsToArray(Envelope $env): array
+    private function correlationIdsToArray(Envelope $env): array
     {
         $out = [];
         if ($env->correlationId instanceof MessageId) {
@@ -109,7 +109,7 @@ public function correlationIdsToArray(Envelope $env): array
     /**
      * @return array<string, mixed>
      */
-    public function endpointsToArray(Envelope $env): array
+    private function endpointsToArray(Envelope $env): array
     {
         $out = [];
         if ($env->source !== null) {

tests/Unit/fixtures/envelopes/event_emit_full.json

@@ -2,7 +2,7 @@
     "arcp": "1.1",
     "id": "msg_01JABC",
     "type": "event.emit",
-    "timestamp": "2026-05-09T13:00:00.000000Z",
+    "timestamp": "2026-05-09T13:00:00.000+00:00",
     "payload": {
         "type": "subscription.backfill_complete",
         "attributes": {