perf(kernel): batch the artifact-lifecycle event triple via appendAll (#59)

The Created->Validating->Validated triple fires unconditionally back-to-back at
three artifact-emission sites — three single-event append transactions (each its
own commit + flow-publish pass) for one logical unit. Added emitAll(sessionId,
payloads) which routes 2+ events through EventStore.appendAll (one transaction,
one publish pass) and falls back to emit() for 0/1. Same events, same order.

Adjacent-but-conditional emits (clarification/approval pause+resume) are left on
emit(): they straddle suspension points, so batching would change observable
ordering.

core/kernel/src/main/kotlin/com/correx/core/kernel/orchestration/SessionOrchestrator.kt

@@ -2074,9 +2074,14 @@ abstract class SessionOrchestrator(
                 ) {
                     return@forEach
                 }
-                emit(sessionId, ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1))
-                emit(sessionId, ArtifactValidatingEvent(slot.name, sessionId, stageId))
-                emit(sessionId, ArtifactValidatedEvent(slot.name, sessionId, stageId))
+                emitAll(
+                    sessionId,
+                    listOf(
+                        ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1),
+                        ArtifactValidatingEvent(slot.name, sessionId, stageId),
+                        ArtifactValidatedEvent(slot.name, sessionId, stageId),
+                    ),
+                )
             }
     }
 
@@ -2198,9 +2203,14 @@ abstract class SessionOrchestrator(
                     )
                     return@forEach
                 }
-                emit(sessionId, ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1))
-                emit(sessionId, ArtifactValidatingEvent(slot.name, sessionId, stageId))
-                emit(sessionId, ArtifactValidatedEvent(slot.name, sessionId, stageId))
+                emitAll(
+                    sessionId,
+                    listOf(
+                        ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1),
+                        ArtifactValidatingEvent(slot.name, sessionId, stageId),
+                        ArtifactValidatedEvent(slot.name, sessionId, stageId),
+                    ),
+                )
             }
     }
 
@@ -2810,9 +2820,14 @@ abstract class SessionOrchestrator(
         // Emit artifact lifecycle events for process_result slots on failure branches.
         // Content was already stored in CAS + cache by dispatchToolCalls for every outcome.
         stageConfig.produces.filter { it.kind.id == "process_result" }.forEach { slot ->
-            emit(sessionId, ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1))
-            emit(sessionId, ArtifactValidatingEvent(slot.name, sessionId, stageId))
-            emit(sessionId, ArtifactValidatedEvent(slot.name, sessionId, stageId))
+            emitAll(
+                sessionId,
+                listOf(
+                    ArtifactCreatedEvent(slot.name, sessionId, stageId, schemaVersion = 1),
+                    ArtifactValidatingEvent(slot.name, sessionId, stageId),
+                    ArtifactValidatedEvent(slot.name, sessionId, stageId),
+                ),
+            )
         }
     }
 
@@ -3192,6 +3207,29 @@ abstract class SessionOrchestrator(
         )
     }
 
+    /** Appends [payloads] as one transaction (one flow-publish pass) for events that belong together. */
+    internal suspend fun emitAll(sessionId: SessionId, payloads: List<EventPayload>) {
+        if (payloads.size <= 1) {
+            payloads.firstOrNull()?.let { emit(sessionId, it) }
+            return
+        }
+        eventStore.appendAll(
+            payloads.map { payload ->
+                NewEvent(
+                    metadata = EventMetadata(
+                        eventId = EventId(UUID.randomUUID().toString()),
+                        sessionId = sessionId,
+                        timestamp = Clock.System.now(),
+                        schemaVersion = 1,
+                        causationId = null,
+                        correlationId = null,
+                    ),
+                    payload = payload,
+                )
+            },
+        )
+    }
+
     // --- token estimation ---
 
     protected open suspend fun estimateTokens(content: String): Int {