diff --git a/src/core/DigitalData.TaskFlow.Application/Common/Behaviors/ValidationBehavior.cs b/src/core/DigitalData.TaskFlow.Application/Common/Behaviors/ValidationBehavior.cs
new file mode 100644
index 0000000..6af7d8d
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Application/Common/Behaviors/ValidationBehavior.cs
@@ -0,0 +1,48 @@
+using FluentValidation;
+using MediatR;
+
+namespace DigitalData.TaskFlow.Application.Common.Behaviors;
+
+/// <summary>
+/// Runs FluentValidation validators before a MediatR request reaches its handler.
+/// </summary>
+/// <typeparam name="TRequest">Request type.</typeparam>
+/// <typeparam name="TResponse">Response type.</typeparam>
+public sealed class ValidationBehavior<TRequest, TResponse>(IEnumerable<IValidator<TRequest>> validators)
+    : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : notnull
+{
+    /// <summary>
+    /// Validates the request and continues the pipeline when validation succeeds.
+    /// </summary>
+    /// <param name="request">Current request instance.</param>
+    /// <param name="next">Next pipeline delegate.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Handler response when validation passes.</returns>
+    /// <exception cref="ValidationException">Thrown when one or more validation errors are found.</exception>
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        if (!validators.Any())
+        {
+            return await next(cancellationToken);
+        }
+
+        var context = new ValidationContext<TRequest>(request);
+        var validationResults = await Task.WhenAll(validators.Select(v => v.ValidateAsync(context, cancellationToken)));
+
+        var failures = validationResults
+            .SelectMany(r => r.Errors)
+            .Where(f => f is not null)
+            .ToList();
+
+        if (failures.Count != 0)
+        {
+            throw new ValidationException(failures);
+        }
+
+        return await next(cancellationToken);
+    }
+}
diff --git a/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IDocumentRepository.cs b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IDocumentRepository.cs
new file mode 100644
index 0000000..058c4fd
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IDocumentRepository.cs
@@ -0,0 +1,17 @@
+using DigitalData.TaskFlow.Domain.Documents;
+
+namespace DigitalData.TaskFlow.Application.Common.Interfaces;
+
+/// <summary>
+/// Defines document-specific data access operations.
+/// </summary>
+public interface IDocumentRepository : IRepository
+{
+    /// <summary>
+    /// Gets document binary content for the given document identifier.
+    /// </summary>
+    /// <param name="id">Document identifier.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Binary document payload.</returns>
+    Task<DocumentBinaryResult> GetAsync(string id, CancellationToken cancellationToken);
+}
diff --git a/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IRepository.cs b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IRepository.cs
new file mode 100644
index 0000000..589ec36
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IRepository.cs
@@ -0,0 +1,8 @@
+namespace DigitalData.TaskFlow.Application.Common.Interfaces;
+
+/// <summary>
+/// Defines a marker contract for repository abstractions in the application layer.
+/// </summary>
+public interface IRepository
+{
+}
diff --git a/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IWorkflowRepository.cs b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IWorkflowRepository.cs
new file mode 100644
index 0000000..87fb6ec
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Application/Common/Interfaces/IWorkflowRepository.cs
@@ -0,0 +1,34 @@
+using DigitalData.TaskFlow.Domain.Closing;
+using DigitalData.TaskFlow.Domain.Workflows;
+
+namespace DigitalData.TaskFlow.Application.Common.Interfaces;
+
+/// <summary>
+/// Defines workflow-specific data access operations for reading and closing workflow items.
+/// </summary>
+public interface IWorkflowRepository : IRepository
+{
+    /// <summary>
+    /// Gets grouped workflow data for the given WISAG user identifier.
+    /// </summary>
+    /// <param name="wisagId">WISAG user identifier.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Workflow data grouped by source.</returns>
+    Task<WorkflowSourcesResponse> GetAsync(int wisagId, CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Applies a closing decision to a workflow process.
+    /// </summary>
+    /// <param name="wisagId">WISAG user identifier.</param>
+    /// <param name="source">Source system name.</param>
+    /// <param name="processId">Process identifier.</param>
+    /// <param name="decision">Closing decision payload.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Closing operation result.</returns>
+    Task<CloseWorkflowResult> CloseAsync(
+        int wisagId,
+        string source,
+        int processId,
+        CloseWorkflowDecision decision,
+        CancellationToken cancellationToken);
+}
diff --git a/src/core/DigitalData.TaskFlow.Application/Common/Mappings/ApplicationMappingProfile.cs b/src/core/DigitalData.TaskFlow.Application/Common/Mappings/ApplicationMappingProfile.cs
new file mode 100644
index 0000000..8797642
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Application/Common/Mappings/ApplicationMappingProfile.cs
@@ -0,0 +1,16 @@
+using AutoMapper;
+
+namespace DigitalData.TaskFlow.Application.Common.Mappings;
+
+/// <summary>
+/// Defines AutoMapper configuration for application-level mappings.
+/// </summary>
+public sealed class ApplicationMappingProfile : Profile
+{
+    /// <summary>
+    /// Initializes mapping configuration.
+    /// </summary>
+    public ApplicationMappingProfile()
+    {
+    }
+}
diff --git a/src/core/DigitalData.TaskFlow.Application/DependencyInjection.cs b/src/core/DigitalData.TaskFlow.Application/DependencyInjection.cs
index 840ce5e..59c36d5 100644
--- a/src/core/DigitalData.TaskFlow.Application/DependencyInjection.cs
+++ b/src/core/DigitalData.TaskFlow.Application/DependencyInjection.cs
@@ -4,6 +4,7 @@ using MediatR;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using System.Reflection;
+using DigitalData.TaskFlow.Application.Common.Behaviors;
 
 namespace DigitalData.TaskFlow.Application;
 
@@ -30,6 +31,7 @@ public static class DependencyInjection
         });
 
         services.AddValidatorsFromAssembly(typeof(DependencyInjection).Assembly);
+        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(ValidationBehavior<,>));
         services.AddAutoMapper(_ => { }, Assembly.GetExecutingAssembly());
 
         return services;