feat(kernel): emit ContextTruncatedEvent on workflow context overflow

DefaultContextPackBuilder already enforced the token budget, but SessionOrchestrator discarded the entriesDropped signal at both build sites — overflow was enforced yet unobserved. Emit ContextTruncatedEvent when entriesDropped>0, matching the router path (open-threads 6.2 contract).

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

@@ -23,6 +23,7 @@ import com.correx.core.context.model.EntryRole
 import com.correx.core.events.events.ApprovalDecisionResolvedEvent
 import com.correx.core.events.events.ApprovalRequestedEvent
 import com.correx.core.events.events.ArtifactCreatedEvent
+import com.correx.core.events.events.ContextTruncatedEvent
 import com.correx.core.events.events.ToolCallAssessedEvent
 import com.correx.core.events.events.ArtifactValidatedEvent
 import com.correx.core.events.events.ArtifactValidatingEvent
@@ -267,6 +268,7 @@ abstract class SessionOrchestrator(
             entries = systemPrompt + schemaEntries + promptEntries + steeringEntries,
             budget = TokenBudget(limit = stageConfig.tokenBudget),
         )
+        emitContextTruncationIfNeeded(sessionId, stageId, contextPack)
 
         var currentContext = contextPack
         var inferenceResult = runInference(
@@ -310,6 +312,7 @@ abstract class SessionOrchestrator(
                 entries = allEntries,
                 budget = TokenBudget(limit = stageConfig.tokenBudget),
             )
+            emitContextTruncationIfNeeded(sessionId, stageId, currentContext)
             inferenceResult = runInference(
                 sessionId, stageId, currentContext, stageConfig, config.stageTimeoutMs, responseFormat,
             )
@@ -937,6 +940,28 @@ abstract class SessionOrchestrator(
 
     // --- event emission ---
 
+    // Surface context-budget overflow as an event on the workflow path. The builder already
+    // enforces the budget (drops oldest/compressible entries, pinning steering + event history);
+    // this records that it happened so replay and operators can see it, mirroring the router path.
+    private suspend fun emitContextTruncationIfNeeded(
+        sessionId: SessionId,
+        stageId: StageId,
+        contextPack: ContextPack,
+    ) {
+        val meta = contextPack.compressionMetadata
+        if (meta.entriesDropped <= 0) return
+        emit(
+            sessionId,
+            ContextTruncatedEvent(
+                sessionId = sessionId,
+                turnId = stageId.value,
+                entriesDropped = meta.entriesDropped,
+                truncatedLayers = meta.truncatedLayers.map { it.name },
+                timestampMs = Clock.System.now().toEpochMilliseconds(),
+            ),
+        )
+    }
+
     internal suspend fun emit(sessionId: SessionId, payload: EventPayload) {
         log.debug("[session {}] emitting event, payload: {}", sessionId.value.take(7), payload)
         eventStore.append(