diff --git a/platform/service/log_ingest_test.go b/platform/service/log_ingest_test.go
index 27824de..f2a0e30 100644
--- a/platform/service/log_ingest_test.go
+++ b/platform/service/log_ingest_test.go
@@ -126,6 +126,30 @@ func TestCoreServicePersistsAndEnforcesImmutableProcessLogSessionMetadata(t *tes
 	}
 }
 
+func TestCoreServiceAcceptsLegacyProcessStreamStartWithoutSessionID(t *testing.T) {
+	svc, sessionToken := newRegisteredLogIngestService(t)
+	startedAt := time.Date(2026, 7, 3, 12, 30, 0, 0, time.UTC)
+	streamID := "run.run-local.server-1.stdout"
+	if _, err := svc.CreateLogStream(domain.LogStream{
+		ID:               streamID,
+		ServerInstanceID: "server-1",
+		Source:           domain.LogStreamSourceProcess,
+		StreamKey:        "stdout",
+		SessionStartedAt: startedAt,
+		StorageBackend:   domain.LogStorageBackendLocalSegments,
+		RetentionPolicy:  "default",
+	}); err != nil {
+		t.Fatalf("create legacy process stream: %v", err)
+	}
+
+	batch := validLogBatch(t, sessionToken, 1, 1)
+	batch.LogStreamID = streamID
+	batch.SessionStartedAt = startedAt
+	if _, err := svc.IngestLogBatch(batch); err != nil {
+		t.Fatalf("ingest legacy process batch: %v", err)
+	}
+}
+
 func TestCoreServiceSerializesConsistentSessionStreamCreation(t *testing.T) {
 	svc, _ := newRegisteredLogIngestService(t)
 	startedAt := time.Date(2026, 7, 3, 12, 30, 0, 0, time.UTC)
diff --git a/platform/validator/log_ingest.go b/platform/validator/log_ingest.go
index d4b478b..2da4837 100644
--- a/platform/validator/log_ingest.go
+++ b/platform/validator/log_ingest.go
@@ -29,7 +29,10 @@ func ValidateLogBatchIngest(batch domain.LogBatchIngest) error {
 	}
 	hasSessionID := strings.TrimSpace(batch.LogSessionID) != ""
 	hasSessionStart := !batch.SessionStartedAt.IsZero()
-	if hasSessionID != hasSessionStart {
+	// Older process streams persisted their start time before Run assigned a
+	// generation id. Keep those batches ingestible so a durable Run spool can
+	// drain without blocking newer generation-scoped console output.
+	if hasSessionID && !hasSessionStart {
 		violations = append(violations, "logSessionId and sessionStartedAt must be provided together")
 	}
 	if (hasSessionID || hasSessionStart) && batch.Source != domain.LogStreamSourceProcess {
diff --git a/platform/validator/resources.go b/platform/validator/resources.go
index 1ec7dac..85b4a22 100644
--- a/platform/validator/resources.go
+++ b/platform/validator/resources.go
@@ -1651,7 +1651,9 @@ func ValidateLogStream(stream domain.LogStream) error {
 	}
 	hasSessionID := strings.TrimSpace(stream.LogSessionID) != ""
 	hasSessionStart := !stream.SessionStartedAt.IsZero()
-	if hasSessionID != hasSessionStart {
+	// Keep legacy process streams with only a persisted start time valid while
+	// requiring the complete pair for new generation-scoped streams.
+	if hasSessionID && !hasSessionStart {
 		violations = append(violations, "logSessionId and sessionStartedAt must be provided together")
 	}
 	if (hasSessionID || hasSessionStart) && stream.Source != domain.LogStreamSourceProcess {