fix(auth): avoid leaking or over-persisting affinity keys

Stop using one-shot idempotency keys as long-lived auth-affinity identifiers and remove raw affinity-key values from debug logs so sticky routing keeps its continuity benefits without creating avoidable memory growth or credential exposure risks.

sdk/api/handlers/handlers.go

@@ -211,8 +211,6 @@ func requestExecutionMetadata(ctx context.Context) map[string]any {
 	if executionSessionID := executionSessionIDFromContext(ctx); executionSessionID != "" {
 		meta[coreexecutor.ExecutionSessionMetadataKey] = executionSessionID
 		meta[authAffinityMetadataKey] = executionSessionID
-	} else if explicitIdempotencyKey != "" {
-		meta[authAffinityMetadataKey] = explicitIdempotencyKey
 	} else if ctx != nil {
 		if ginCtx, ok := ctx.Value("gin").(*gin.Context); ok && ginCtx != nil {
 			if apiKey, exists := ginCtx.Get("apiKey"); exists && apiKey != nil {