diff --git a/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowDecision.cs b/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowDecision.cs
new file mode 100644
index 0000000..3cbcf50
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowDecision.cs
@@ -0,0 +1,22 @@
+namespace DigitalData.TaskFlow.Domain.Closing;
+
+/// <summary>
+/// Represents the user decision payload for closing a workflow process.
+/// </summary>
+public sealed record CloseWorkflowDecision
+{
+    /// <summary>
+    /// Gets the selected closing method identifier.
+    /// </summary>
+    public required int ClosingMethodId { get; init; }
+
+    /// <summary>
+    /// Gets the optional comment attached to the decision.
+    /// </summary>
+    public string? Comment { get; init; }
+
+    /// <summary>
+    /// Gets the optional rejection reason identifier.
+    /// </summary>
+    public int? RejectionReasonId { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowResult.cs b/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowResult.cs
new file mode 100644
index 0000000..7ee69b3
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Closing/CloseWorkflowResult.cs
@@ -0,0 +1,17 @@
+namespace DigitalData.TaskFlow.Domain.Closing;
+
+/// <summary>
+/// Represents the result of a workflow closing operation.
+/// </summary>
+public sealed record CloseWorkflowResult
+{
+    /// <summary>
+    /// Gets the process identifier.
+    /// </summary>
+    public required int ProcessId { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether the process was closed successfully.
+    /// </summary>
+    public required bool IsClosed { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Common/ApiEnvelope.cs b/src/core/DigitalData.TaskFlow.Domain/Common/ApiEnvelope.cs
new file mode 100644
index 0000000..b96ab0e
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Common/ApiEnvelope.cs
@@ -0,0 +1,18 @@
+namespace DigitalData.TaskFlow.Domain.Common;
+
+/// <summary>
+/// Represents the standard API envelope that contains meta information and payload data.
+/// </summary>
+/// <typeparam name="T">Type of the payload in the response.</typeparam>
+public sealed record ApiEnvelope<T>
+{
+    /// <summary>
+    /// Gets the list of metadata entries describing the business result.
+    /// </summary>
+    public required IReadOnlyList<MetaEntry> Meta { get; init; }
+
+    /// <summary>
+    /// Gets the payload data returned by the endpoint.
+    /// </summary>
+    public T? Data { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Common/MetaEntry.cs b/src/core/DigitalData.TaskFlow.Domain/Common/MetaEntry.cs
new file mode 100644
index 0000000..6d99b83
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Common/MetaEntry.cs
@@ -0,0 +1,17 @@
+namespace DigitalData.TaskFlow.Domain.Common;
+
+/// <summary>
+/// Represents a single metadata item describing the business result state of an API response.
+/// </summary>
+public sealed record MetaEntry
+{
+    /// <summary>
+    /// Gets the domain-specific result code.
+    /// </summary>
+    public required int Code { get; init; }
+
+    /// <summary>
+    /// Gets the human-readable message that belongs to <see cref="Code"/>.
+    /// </summary>
+    public required string Message { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Documents/DocumentBinaryResult.cs b/src/core/DigitalData.TaskFlow.Domain/Documents/DocumentBinaryResult.cs
new file mode 100644
index 0000000..2f072fa
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Documents/DocumentBinaryResult.cs
@@ -0,0 +1,27 @@
+namespace DigitalData.TaskFlow.Domain.Documents;
+
+/// <summary>
+/// Represents binary document content returned by the document endpoint.
+/// </summary>
+public sealed record DocumentBinaryResult
+{
+    /// <summary>
+    /// Gets the raw binary content.
+    /// </summary>
+    public required byte[] Content { get; init; }
+
+    /// <summary>
+    /// Gets the MIME content type.
+    /// </summary>
+    public required string ContentType { get; init; }
+
+    /// <summary>
+    /// Gets the file name used for download.
+    /// </summary>
+    public required string FileName { get; init; }
+
+    /// <summary>
+    /// Gets the content length in bytes.
+    /// </summary>
+    public required long Length { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Enums/MetaCode.cs b/src/core/DigitalData.TaskFlow.Domain/Enums/MetaCode.cs
new file mode 100644
index 0000000..168fc00
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Enums/MetaCode.cs
@@ -0,0 +1,42 @@
+namespace DigitalData.TaskFlow.Domain.Enums;
+
+/// <summary>
+/// Defines domain-level result codes used in API meta responses.
+/// </summary>
+public enum MetaCode
+{
+    /// <summary>
+    /// Operation completed successfully.
+    /// </summary>
+    Ok = 0,
+
+    /// <summary>
+    /// Request is valid but no open workflows are available.
+    /// </summary>
+    NoOpenWorkflows = 1,
+
+    /// <summary>
+    /// Caller has no access to the requested resource.
+    /// </summary>
+    NoAccess = 2,
+
+    /// <summary>
+    /// Request is invalid or authentication failed according to endpoint rules.
+    /// </summary>
+    InvalidRequest = 4,
+
+    /// <summary>
+    /// Internal server error occurred.
+    /// </summary>
+    InternalError = 5,
+
+    /// <summary>
+    /// Requested resource was not found.
+    /// </summary>
+    NotFound = 6,
+
+    /// <summary>
+    /// Target workflow was already closed.
+    /// </summary>
+    AlreadyClosed = 7
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/ApprovalItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/ApprovalItem.cs
new file mode 100644
index 0000000..177368f
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/ApprovalItem.cs
@@ -0,0 +1,32 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents a completed approval action for a workflow process.
+/// </summary>
+public sealed record ApprovalItem
+{
+    /// <summary>
+    /// Gets the process identifier.
+    /// </summary>
+    public required int ProcessId { get; init; }
+
+    /// <summary>
+    /// Gets the approval sequence index.
+    /// </summary>
+    public required int Sequence { get; init; }
+
+    /// <summary>
+    /// Gets the user name or identifier of the approver.
+    /// </summary>
+    public required string ApprovedBy { get; init; }
+
+    /// <summary>
+    /// Gets the UTC timestamp when approval was recorded.
+    /// </summary>
+    public required DateTime ApprovedAtUtc { get; init; }
+
+    /// <summary>
+    /// Gets the optional approval comment.
+    /// </summary>
+    public string? Comment { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/ClosingMethodItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/ClosingMethodItem.cs
new file mode 100644
index 0000000..223f734
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/ClosingMethodItem.cs
@@ -0,0 +1,27 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents a workflow closing option available for user decision.
+/// </summary>
+public sealed record ClosingMethodItem
+{
+    /// <summary>
+    /// Gets the closing method identifier.
+    /// </summary>
+    public required int ClosingMethodId { get; init; }
+
+    /// <summary>
+    /// Gets the display name of the method.
+    /// </summary>
+    public required string Name { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether a comment is mandatory for this method.
+    /// </summary>
+    public required bool CommentRequired { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether this method represents a rejection.
+    /// </summary>
+    public required bool IsRejection { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/ContractsSourceBlock.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/ContractsSourceBlock.cs
new file mode 100644
index 0000000..54c2cd9
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/ContractsSourceBlock.cs
@@ -0,0 +1,37 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents workflow data for the Contracts source system.
+/// </summary>
+public sealed record ContractsSourceBlock : SourceBlock
+{
+    /// <summary>
+    /// Gets available approval profiles.
+    /// </summary>
+    public required IReadOnlyList<ProfileItem> Profiles { get; init; }
+
+    /// <summary>
+    /// Gets workflow listing items.
+    /// </summary>
+    public required IReadOnlyList<WorkflowListingItem> Listing { get; init; }
+
+    /// <summary>
+    /// Gets already executed approvals.
+    /// </summary>
+    public required IReadOnlyList<ApprovalItem> Approvals { get; init; }
+
+    /// <summary>
+    /// Gets document references for workflows.
+    /// </summary>
+    public required IReadOnlyList<DocumentReferenceItem> Documents { get; init; }
+
+    /// <summary>
+    /// Gets available closing methods for workflows.
+    /// </summary>
+    public required IReadOnlyList<ClosingMethodItem> ClosingMethods { get; init; }
+
+    /// <summary>
+    /// Gets available rejection reasons for rejection-type methods.
+    /// </summary>
+    public required IReadOnlyList<RejectionReasonItem> RejectionReasons { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/DocumentReferenceItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/DocumentReferenceItem.cs
new file mode 100644
index 0000000..c90f399
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/DocumentReferenceItem.cs
@@ -0,0 +1,27 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents a lightweight document reference linked to a workflow process.
+/// </summary>
+public sealed record DocumentReferenceItem
+{
+    /// <summary>
+    /// Gets the document identifier used for binary retrieval.
+    /// </summary>
+    public required string Id { get; init; }
+
+    /// <summary>
+    /// Gets the process identifier.
+    /// </summary>
+    public required int ProcessId { get; init; }
+
+    /// <summary>
+    /// Gets the document title.
+    /// </summary>
+    public required string Title { get; init; }
+
+    /// <summary>
+    /// Gets the document subtitle.
+    /// </summary>
+    public required string Subtitle { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/FerdinandSourceBlock.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/FerdinandSourceBlock.cs
new file mode 100644
index 0000000..9872378
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/FerdinandSourceBlock.cs
@@ -0,0 +1,37 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents workflow data for the Ferdinand source system.
+/// </summary>
+public sealed record FerdinandSourceBlock : SourceBlock
+{
+    /// <summary>
+    /// Gets available approval profiles.
+    /// </summary>
+    public required IReadOnlyList<ProfileItem> Profiles { get; init; }
+
+    /// <summary>
+    /// Gets workflow listing items.
+    /// </summary>
+    public required IReadOnlyList<WorkflowListingItem> Listing { get; init; }
+
+    /// <summary>
+    /// Gets already executed approvals.
+    /// </summary>
+    public required IReadOnlyList<ApprovalItem> Approvals { get; init; }
+
+    /// <summary>
+    /// Gets document references for workflows.
+    /// </summary>
+    public required IReadOnlyList<DocumentReferenceItem> Documents { get; init; }
+
+    /// <summary>
+    /// Gets available closing methods for workflows.
+    /// </summary>
+    public required IReadOnlyList<ClosingMethodItem> ClosingMethods { get; init; }
+
+    /// <summary>
+    /// Gets available rejection reasons for rejection-type methods.
+    /// </summary>
+    public required IReadOnlyList<RejectionReasonItem> RejectionReasons { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/ProfileItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/ProfileItem.cs
new file mode 100644
index 0000000..a71a46d
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/ProfileItem.cs
@@ -0,0 +1,22 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents an approval profile for workflow processing.
+/// </summary>
+public sealed record ProfileItem
+{
+    /// <summary>
+    /// Gets the profile identifier.
+    /// </summary>
+    public required int ProfileId { get; init; }
+
+    /// <summary>
+    /// Gets the display title of the profile.
+    /// </summary>
+    public required string Title { get; init; }
+
+    /// <summary>
+    /// Gets the optional priority value.
+    /// </summary>
+    public int? Priority { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/RejectionReasonItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/RejectionReasonItem.cs
new file mode 100644
index 0000000..fddaccb
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/RejectionReasonItem.cs
@@ -0,0 +1,17 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents a rejection reason that can be selected for rejection methods.
+/// </summary>
+public sealed record RejectionReasonItem
+{
+    /// <summary>
+    /// Gets the rejection reason identifier.
+    /// </summary>
+    public required int RejectionReasonId { get; init; }
+
+    /// <summary>
+    /// Gets the display name of the rejection reason.
+    /// </summary>
+    public required string Name { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/SourceBlock.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/SourceBlock.cs
new file mode 100644
index 0000000..8808ae2
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/SourceBlock.cs
@@ -0,0 +1,12 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Base type for source-specific workflow blocks.
+/// </summary>
+public abstract record SourceBlock
+{
+    /// <summary>
+    /// Gets the source system name.
+    /// </summary>
+    public required string Source { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowListingItem.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowListingItem.cs
new file mode 100644
index 0000000..77feff1
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowListingItem.cs
@@ -0,0 +1,87 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents a single workflow listing row.
+/// </summary>
+public sealed record WorkflowListingItem
+{
+    /// <summary>
+    /// Gets the process identifier.
+    /// </summary>
+    public required int ProcessId { get; init; }
+
+    /// <summary>
+    /// Gets the profile identifier associated with the process.
+    /// </summary>
+    public required int ProfileId { get; init; }
+
+    /// <summary>
+    /// Gets the voucher type.
+    /// </summary>
+    public required string VoucherType { get; init; }
+
+    /// <summary>
+    /// Gets the voucher number.
+    /// </summary>
+    public required string VoucherNumber { get; init; }
+
+    /// <summary>
+    /// Gets the voucher date.
+    /// </summary>
+    public required DateOnly VoucherDate { get; init; }
+
+    /// <summary>
+    /// Gets the cost center number.
+    /// </summary>
+    public required string CostCenter { get; init; }
+
+    /// <summary>
+    /// Gets the cost center description.
+    /// </summary>
+    public required string CostCenterDescription { get; init; }
+
+    /// <summary>
+    /// Gets the client number.
+    /// </summary>
+    public required int ClientNumber { get; init; }
+
+    /// <summary>
+    /// Gets the client name.
+    /// </summary>
+    public required string ClientName { get; init; }
+
+    /// <summary>
+    /// Gets the supplier number.
+    /// </summary>
+    public required string SupplierNumber { get; init; }
+
+    /// <summary>
+    /// Gets the supplier name.
+    /// </summary>
+    public required string SupplierName { get; init; }
+
+    /// <summary>
+    /// Gets the net amount.
+    /// </summary>
+    public required decimal NetAmount { get; init; }
+
+    /// <summary>
+    /// Gets the gross amount.
+    /// </summary>
+    public required decimal GrossAmount { get; init; }
+
+    /// <summary>
+    /// Gets the discount amount.
+    /// </summary>
+    public required decimal DiscountAmount { get; init; }
+
+    /// <summary>
+    /// Gets the currency.
+    /// </summary>
+    public required string Currency { get; init; }
+
+    /// <summary>
+    /// Gets the priority value.
+    /// </summary>
+    public required int Priority { get; init; }
+}
diff --git a/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowSourcesResponse.cs b/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowSourcesResponse.cs
new file mode 100644
index 0000000..ff36086
--- /dev/null
+++ b/src/core/DigitalData.TaskFlow.Domain/Workflows/WorkflowSourcesResponse.cs
@@ -0,0 +1,12 @@
+namespace DigitalData.TaskFlow.Domain.Workflows;
+
+/// <summary>
+/// Represents the workflow payload grouped by source systems.
+/// </summary>
+public sealed record WorkflowSourcesResponse
+{
+    /// <summary>
+    /// Gets the source blocks included in the response.
+    /// </summary>
+    public required IReadOnlyList<SourceBlock> Sources { get; init; }
+}