feat(workflows): Phase 1 backend — WorkflowDefinition model, persistence, IPC, sidecar execution

Introduce WorkflowDefinition as a first-class entity alongside PatternDefinition.

Shared domain:
- src/shared/domain/workflow.ts: new WorkflowDefinition, WorkflowGraph,
  WorkflowNode/Edge/Config types, normalization, TS-side validation, and
  buildWorkflowExecutionPattern (synthetic pattern bridge for session plumbing)
- workspace.ts: add workflows[] and selectedWorkflowId
- session.ts: add optional workflowId to SessionRecord
- runTimeline.ts: add optional workflowId/workflowName to run records
- sessionLibrary.ts: workflow-aware session search

IPC / main process:
- contracts/channels.ts, contracts/ipc.ts: workflow CRUD channels
- preload/index.ts: expose saveWorkflow, deleteWorkflow, createWorkflowSession
- ipc/registerIpcHandlers.ts: register workflow handlers
- persistence/workspaceRepository.ts: load/save/normalize workflows
- AryxAppService.ts: saveWorkflow, deleteWorkflow, createWorkflowSession,
  resolveSessionExecutionDefinition, workflow-aware turn/run plumbing

Sidecar protocol:
- contracts/sidecar.ts: ValidateWorkflowCommand, WorkflowValidationEvent,
  optional workflow on RunTurnCommand
- sidecarProcess.ts: validate-workflow command dispatch and event handling
- Contracts/ProtocolModels.cs: workflow DTOs and validate-workflow DTOs
- Services/SidecarProtocolHost.cs: validate-workflow command handler
- Services/CopilotWorkflowRunner.cs: workflow-aware build and checkpoint path
- Services/WorkflowValidator.cs: graph validation (connectivity, start/end,
  fan-out/in arity, path reachability)
- Services/WorkflowRunner.cs: WorkflowDefinitionDto -> Agent Framework Workflow
  builder (direct, fan-out, fan-in edges; agent executor binding)

Project: bump both csproj from net9.0 to net10.0

Tests:
- tests/shared/workflow.test.ts: TS workflow validation and pattern synthesis
- tests/main/appServiceWorkflow.test.ts: saveWorkflow / createWorkflowSession
- tests/Aryx.AgentHost.Tests/SidecarProtocolHostTests.cs: ValidateWorkflowCommand
- Fix two stale workspace fixtures missing workflows field

Validation: tsc clean, bun test 367/367 pass, dotnet test 244/244 pass, bun run build succeeds.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/src/Aryx.AgentHost/Aryx.AgentHost.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <SatelliteResourceLanguages>en</SatelliteResourceLanguages>

sidecar/src/Aryx.AgentHost/Contracts/ProtocolModels.cs

@@ -1,3 +1,4 @@
+using System.Text.Json;
 using System.Text.Json.Serialization;
 
 namespace Aryx.AgentHost.Contracts;
@@ -66,6 +67,125 @@ public sealed class PatternDefinitionDto
     public string UpdatedAt { get; init; } = string.Empty;
 }
 
+public sealed class WorkflowPositionDto
+{
+    public double X { get; init; }
+    public double Y { get; init; }
+}
+
+public sealed class WorkflowNodeConfigDto
+{
+    public string Kind { get; init; } = string.Empty;
+    public string? InputType { get; init; }
+    public string? OutputType { get; init; }
+    public string Id { get; init; } = string.Empty;
+    public string Name { get; init; } = string.Empty;
+    public string Description { get; init; } = string.Empty;
+    public string Instructions { get; init; } = string.Empty;
+    public string Model { get; init; } = string.Empty;
+    public string? ReasoningEffort { get; init; }
+    public PatternAgentCopilotConfigDto? Copilot { get; init; }
+    public string? WorkspaceAgentId { get; init; }
+    public string? Implementation { get; init; }
+    public string? FunctionRef { get; init; }
+    public IReadOnlyDictionary<string, JsonElement>? Parameters { get; init; }
+    public string? WorkflowId { get; init; }
+    public WorkflowDefinitionDto? InlineWorkflow { get; init; }
+    public string? PortId { get; init; }
+    public string? RequestType { get; init; }
+    public string? ResponseType { get; init; }
+    public string? Prompt { get; init; }
+}
+
+public sealed class WorkflowNodeDto
+{
+    public string Id { get; init; } = string.Empty;
+    public string Kind { get; init; } = string.Empty;
+    public string Label { get; init; } = string.Empty;
+    public WorkflowPositionDto Position { get; init; } = new();
+    public int? Order { get; init; }
+    public WorkflowNodeConfigDto Config { get; init; } = new();
+}
+
+public sealed class WorkflowConditionRuleDto
+{
+    public string PropertyPath { get; init; } = string.Empty;
+    public string Operator { get; init; } = string.Empty;
+    public string Value { get; init; } = string.Empty;
+}
+
+public sealed class EdgeConditionDto
+{
+    public string Type { get; init; } = string.Empty;
+    public string? TypeName { get; init; }
+    public string? Expression { get; init; }
+    public string? Combinator { get; init; }
+    public IReadOnlyList<WorkflowConditionRuleDto> Rules { get; init; } = [];
+}
+
+public sealed class FanOutConfigDto
+{
+    public string Strategy { get; init; } = "broadcast";
+    public string? PartitionExpression { get; init; }
+}
+
+public sealed class WorkflowEdgeDto
+{
+    public string Id { get; init; } = string.Empty;
+    public string Source { get; init; } = string.Empty;
+    public string Target { get; init; } = string.Empty;
+    public string Kind { get; init; } = "direct";
+    public EdgeConditionDto? Condition { get; init; }
+    public string? Label { get; init; }
+    public FanOutConfigDto? FanOutConfig { get; init; }
+}
+
+public sealed class WorkflowGraphDto
+{
+    public IReadOnlyList<WorkflowNodeDto> Nodes { get; init; } = [];
+    public IReadOnlyList<WorkflowEdgeDto> Edges { get; init; } = [];
+}
+
+public sealed class WorkflowCheckpointSettingsDto
+{
+    public bool Enabled { get; init; }
+}
+
+public sealed class WorkflowTelemetrySettingsDto
+{
+    public bool? OpenTelemetry { get; init; }
+    public bool? SensitiveData { get; init; }
+}
+
+public sealed class WorkflowStateScopeDto
+{
+    public string Name { get; init; } = string.Empty;
+    public string? Description { get; init; }
+    public IReadOnlyDictionary<string, JsonElement>? InitialValues { get; init; }
+}
+
+public sealed class WorkflowSettingsDto
+{
+    public WorkflowCheckpointSettingsDto Checkpointing { get; init; } = new();
+    public string ExecutionMode { get; init; } = "off-thread";
+    public int? MaxIterations { get; init; }
+    public ApprovalPolicyDto? ApprovalPolicy { get; init; }
+    public IReadOnlyList<WorkflowStateScopeDto> StateScopes { get; init; } = [];
+    public WorkflowTelemetrySettingsDto? Telemetry { get; init; }
+}
+
+public sealed class WorkflowDefinitionDto
+{
+    public string Id { get; init; } = string.Empty;
+    public string Name { get; init; } = string.Empty;
+    public string Description { get; init; } = string.Empty;
+    public bool? IsFavorite { get; init; }
+    public WorkflowGraphDto Graph { get; init; } = new();
+    public WorkflowSettingsDto Settings { get; init; } = new();
+    public string CreatedAt { get; init; } = string.Empty;
+    public string UpdatedAt { get; init; } = string.Empty;
+}
+
 public sealed class ApprovalPolicyDto
 {
     public IReadOnlyList<ApprovalCheckpointRuleDto> Rules { get; init; } = [];
@@ -105,6 +225,15 @@ public sealed class PatternValidationIssueDto
     public string Message { get; init; } = string.Empty;
 }
 
+public sealed class WorkflowValidationIssueDto
+{
+    public string Level { get; init; } = "error";
+    public string? Field { get; init; }
+    public string Message { get; init; } = string.Empty;
+    public string? NodeId { get; init; }
+    public string? EdgeId { get; init; }
+}
+
 public sealed class SidecarModeCapabilityDto
 {
     public bool Available { get; init; }
@@ -177,6 +306,11 @@ public sealed class ValidatePatternCommandDto : SidecarCommandEnvelope
     public PatternDefinitionDto Pattern { get; init; } = new();
 }
 
+public sealed class ValidateWorkflowCommandDto : SidecarCommandEnvelope
+{
+    public WorkflowDefinitionDto Workflow { get; init; } = new();
+}
+
 public sealed class RunTurnCommandDto : SidecarCommandEnvelope
 {
     public string SessionId { get; init; } = string.Empty;
@@ -186,6 +320,7 @@ public sealed class RunTurnCommandDto : SidecarCommandEnvelope
     public string MessageMode { get; init; } = "enqueue";
     public string? ProjectInstructions { get; init; }
     public PatternDefinitionDto Pattern { get; init; } = new();
+    public WorkflowDefinitionDto? Workflow { get; init; }
     public IReadOnlyList<ChatMessageDto> Messages { get; init; } = [];
     public RunTurnPromptInvocationDto? PromptInvocation { get; init; }
     public RunTurnToolingConfigDto? Tooling { get; init; }
@@ -330,6 +465,11 @@ public sealed class PatternValidationEventDto : SidecarEventDto
     public IReadOnlyList<PatternValidationIssueDto> Issues { get; init; } = [];
 }
 
+public sealed class WorkflowValidationEventDto : SidecarEventDto
+{
+    public IReadOnlyList<WorkflowValidationIssueDto> Issues { get; init; } = [];
+}
+
 public sealed class TurnDeltaEventDto : SidecarEventDto
 {
     public string SessionId { get; init; } = string.Empty;

sidecar/src/Aryx.AgentHost/Services/CopilotWorkflowRunner.cs

@@ -12,14 +12,17 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
 {
     private const string HandoffFunctionPrefix = "handoff_to_";
     private readonly PatternValidator _patternValidator;
+    private readonly WorkflowValidator _workflowValidator;
+    private readonly WorkflowRunner _workflowRunner = new();
     private readonly CopilotApprovalCoordinator _approvalCoordinator = new();
     private readonly CopilotUserInputCoordinator _userInputCoordinator = new();
     private readonly CopilotMcpOAuthCoordinator _mcpOAuthCoordinator = new();
     private readonly CopilotExitPlanModeCoordinator _exitPlanModeCoordinator = new();
 
-    public CopilotWorkflowRunner(PatternValidator patternValidator)
+    public CopilotWorkflowRunner(PatternValidator patternValidator, WorkflowValidator? workflowValidator = null)
     {
         _patternValidator = patternValidator;
+        _workflowValidator = workflowValidator ?? new WorkflowValidator();
     }
 
     public async Task<IReadOnlyList<ChatMessageDto>> RunTurnAsync(
@@ -32,10 +35,12 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
         Func<ExitPlanModeRequestedEventDto, Task> onExitPlanMode,
         CancellationToken cancellationToken)
     {
-        PatternValidationIssueDto? validationError = _patternValidator.Validate(command.Pattern).FirstOrDefault();
+        string? validationError = command.Workflow is null
+            ? _patternValidator.Validate(command.Pattern).FirstOrDefault()?.Message
+            : _workflowValidator.Validate(command.Workflow).FirstOrDefault()?.Message;
         if (validationError is not null)
         {
-            throw new InvalidOperationException(validationError.Message);
+            throw new InvalidOperationException(validationError);
         }
 
         CopilotTurnExecutionState state = new(command);
@@ -79,7 +84,9 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                 },
                 runCancellation.Token);
             ConfigureHookLifecycleEventSuppression(state, bundle);
-            Workflow workflow = bundle.BuildWorkflow(command.Pattern);
+            Workflow workflow = command.Workflow is null
+                ? bundle.BuildWorkflow(command.Pattern)
+                : _workflowRunner.BuildWorkflow(command.Workflow, command.Pattern, bundle.Agents);
             List<ChatMessage> inputMessages = command.Messages.Select(WorkflowTranscriptProjector.ToChatMessage).ToList();
             WorkflowTranscriptProjector.AttachMessageMode(inputMessages, command.MessageMode);
 
@@ -145,6 +152,11 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
     internal static bool ShouldEnableWorkflowCheckpointing(RunTurnCommandDto command)
     {
         ArgumentNullException.ThrowIfNull(command);
+        if (command.Workflow is not null)
+        {
+            return command.Workflow.Settings.Checkpointing.Enabled;
+        }
+
         return string.Equals(command.Pattern.Mode, "handoff", StringComparison.OrdinalIgnoreCase);
     }
 

sidecar/src/Aryx.AgentHost/Services/SidecarProtocolHost.cs

@@ -11,6 +11,7 @@ public sealed class SidecarProtocolHost
 {
     private const string DescribeCapabilitiesCommandType = "describe-capabilities";
     private const string ValidatePatternCommandType = "validate-pattern";
+    private const string ValidateWorkflowCommandType = "validate-workflow";
     private const string RunTurnCommandType = "run-turn";
     private const string CancelTurnCommandType = "cancel-turn";
     private const string ResolveApprovalCommandType = "resolve-approval";
@@ -42,6 +43,7 @@ public sealed class SidecarProtocolHost
 
     private readonly Func<CancellationToken, Task<SidecarCapabilitiesDto>> _capabilitiesProvider;
     private readonly PatternValidator _patternValidator;
+    private readonly WorkflowValidator _workflowValidator;
     private readonly ITurnWorkflowRunner _workflowRunner;
     private readonly ICopilotSessionManager _sessionManager;
     private readonly JsonSerializerOptions _jsonOptions;
@@ -53,7 +55,7 @@ public sealed class SidecarProtocolHost
         new(StringComparer.Ordinal);
 
     public SidecarProtocolHost()
-        : this(new PatternValidator())
+        : this(new PatternValidator(), new WorkflowValidator())
     {
     }
 
@@ -62,9 +64,20 @@ public sealed class SidecarProtocolHost
         ITurnWorkflowRunner? workflowRunner = null,
         Func<CancellationToken, Task<SidecarCapabilitiesDto>>? capabilitiesProvider = null,
         ICopilotSessionManager? sessionManager = null)
+        : this(patternValidator, new WorkflowValidator(), workflowRunner, capabilitiesProvider, sessionManager)
+    {
+    }
+
+    public SidecarProtocolHost(
+        PatternValidator patternValidator,
+        WorkflowValidator workflowValidator,
+        ITurnWorkflowRunner? workflowRunner = null,
+        Func<CancellationToken, Task<SidecarCapabilitiesDto>>? capabilitiesProvider = null,
+        ICopilotSessionManager? sessionManager = null)
     {
         _patternValidator = patternValidator;
-        _workflowRunner = workflowRunner ?? new CopilotWorkflowRunner(_patternValidator);
+        _workflowValidator = workflowValidator;
+        _workflowRunner = workflowRunner ?? new CopilotWorkflowRunner(_patternValidator, _workflowValidator);
         _capabilitiesProvider = capabilitiesProvider ?? BuildCapabilitiesAsync;
         _sessionManager = sessionManager ?? new CopilotSessionManager();
         _jsonOptions = JsonSerialization.CreateWebOptions();
@@ -74,6 +87,7 @@ public sealed class SidecarProtocolHost
         {
             [DescribeCapabilitiesCommandType] = HandleDescribeCapabilitiesAsync,
             [ValidatePatternCommandType] = HandleValidatePatternAsync,
+            [ValidateWorkflowCommandType] = HandleValidateWorkflowAsync,
             [RunTurnCommandType] = HandleRunTurnAsync,
             [CancelTurnCommandType] = HandleCancelTurnAsync,
             [ResolveApprovalCommandType] = HandleResolveApprovalAsync,
@@ -180,6 +194,18 @@ public sealed class SidecarProtocolHost
         }, context.CancellationToken).ConfigureAwait(false);
     }
 
+    private async Task HandleValidateWorkflowAsync(CommandContext context)
+    {
+        ValidateWorkflowCommandDto command = DeserializeCommand<ValidateWorkflowCommandDto>(context);
+
+        await WriteAsync(context.Output, new WorkflowValidationEventDto
+        {
+            Type = "workflow-validation",
+            RequestId = context.Envelope.RequestId,
+            Issues = _workflowValidator.Validate(command.Workflow),
+        }, context.CancellationToken).ConfigureAwait(false);
+    }
+
     private async Task HandleRunTurnAsync(CommandContext context)
     {
         RunTurnCommandDto command = DeserializeCommand<RunTurnCommandDto>(context);

sidecar/src/Aryx.AgentHost/Services/WorkflowRunner.cs

@@ -0,0 +1,95 @@
+using Aryx.AgentHost.Contracts;
+using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.Workflows;
+using Microsoft.Agents.AI.Workflows.Specialized;
+
+namespace Aryx.AgentHost.Services;
+
+internal sealed class WorkflowRunner
+{
+    public Workflow BuildWorkflow(
+        WorkflowDefinitionDto workflowDefinition,
+        PatternDefinitionDto patternDefinition,
+        IReadOnlyList<AIAgent> agents)
+    {
+        ArgumentNullException.ThrowIfNull(workflowDefinition);
+        ArgumentNullException.ThrowIfNull(patternDefinition);
+        ArgumentNullException.ThrowIfNull(agents);
+
+        WorkflowNodeDto startNode = workflowDefinition.Graph.Nodes.Single(node =>
+            string.Equals(node.Kind, "start", StringComparison.OrdinalIgnoreCase));
+        WorkflowNodeDto endNode = workflowDefinition.Graph.Nodes.Single(node =>
+            string.Equals(node.Kind, "end", StringComparison.OrdinalIgnoreCase));
+
+        Dictionary<string, AIAgent> agentMap = patternDefinition.Agents
+            .Zip(agents, (definition, agent) => (definition.Id, agent))
+            .ToDictionary(pair => pair.Id, pair => pair.agent, StringComparer.Ordinal);
+
+        Dictionary<string, ExecutorBinding> bindings = new(StringComparer.Ordinal);
+        foreach (WorkflowNodeDto node in workflowDefinition.Graph.Nodes)
+        {
+            bindings[node.Id] = CreateExecutorBinding(node, agentMap);
+        }
+
+        WorkflowBuilder builder = new(bindings[startNode.Id]);
+
+        foreach (WorkflowEdgeDto edge in workflowDefinition.Graph.Edges.Where(edge =>
+                     string.Equals(edge.Kind, "direct", StringComparison.OrdinalIgnoreCase)))
+        {
+            builder.AddEdge(bindings[edge.Source], bindings[edge.Target]);
+        }
+
+        foreach (IGrouping<string, WorkflowEdgeDto> fanOutGroup in workflowDefinition.Graph.Edges
+                     .Where(edge => string.Equals(edge.Kind, "fan-out", StringComparison.OrdinalIgnoreCase))
+                     .GroupBy(edge => edge.Source, StringComparer.Ordinal))
+        {
+            builder.AddFanOutEdge(
+                bindings[fanOutGroup.Key],
+                fanOutGroup.Select(edge => bindings[edge.Target]).ToArray());
+        }
+
+        foreach (IGrouping<string, WorkflowEdgeDto> fanInGroup in workflowDefinition.Graph.Edges
+                     .Where(edge => string.Equals(edge.Kind, "fan-in", StringComparison.OrdinalIgnoreCase))
+                     .GroupBy(edge => edge.Target, StringComparer.Ordinal))
+        {
+            builder.AddFanInBarrierEdge(
+                fanInGroup.Select(edge => bindings[edge.Source]).ToArray(),
+                bindings[fanInGroup.Key]);
+        }
+
+        if (!string.IsNullOrWhiteSpace(workflowDefinition.Name))
+        {
+            builder = builder.WithName(workflowDefinition.Name);
+        }
+
+        return builder.WithOutputFrom(bindings[endNode.Id]).Build();
+    }
+
+    private static ExecutorBinding CreateExecutorBinding(
+        WorkflowNodeDto node,
+        IReadOnlyDictionary<string, AIAgent> agentMap)
+    {
+        if (string.Equals(node.Kind, "start", StringComparison.OrdinalIgnoreCase))
+        {
+            return new ChatForwardingExecutor(node.Id);
+        }
+
+        if (string.Equals(node.Kind, "end", StringComparison.OrdinalIgnoreCase))
+        {
+            return new WorkflowOutputMessagesExecutor();
+        }
+
+        if (string.Equals(node.Kind, "agent", StringComparison.OrdinalIgnoreCase))
+        {
+            string agentId = !string.IsNullOrWhiteSpace(node.Config.Id) ? node.Config.Id : node.Id;
+            if (!agentMap.TryGetValue(agentId, out AIAgent? agent))
+            {
+                throw new InvalidOperationException($"Workflow node \"{node.Id}\" references unknown agent \"{agentId}\".");
+            }
+
+            return agent.BindAsExecutor(CopilotAgentBundle.CreateAgentHostOptions());
+        }
+
+        throw new NotSupportedException($"Workflow node kind \"{node.Kind}\" is not executable yet.");
+    }
+}

sidecar/src/Aryx.AgentHost/Services/WorkflowValidator.cs

@@ -0,0 +1,292 @@
+using Aryx.AgentHost.Contracts;
+
+namespace Aryx.AgentHost.Services;
+
+public sealed class WorkflowValidator
+{
+    private static readonly HashSet<string> ExecutableNodeKinds = new(StringComparer.OrdinalIgnoreCase)
+    {
+        "start",
+        "end",
+        "agent",
+    };
+
+    public IReadOnlyList<WorkflowValidationIssueDto> Validate(WorkflowDefinitionDto workflow)
+    {
+        List<WorkflowValidationIssueDto> issues = [];
+
+        if (string.IsNullOrWhiteSpace(workflow.Name))
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "name",
+                Message = "Workflow name is required.",
+            });
+        }
+
+        if (workflow.Graph.Nodes.Count == 0)
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "graph",
+                Message = "Workflow graph must include nodes.",
+            });
+            return issues;
+        }
+
+        Dictionary<string, WorkflowNodeDto> nodesById = new(StringComparer.Ordinal);
+        HashSet<string> edgeIds = new(StringComparer.Ordinal);
+        Dictionary<string, int> incomingCounts = new(StringComparer.Ordinal);
+        Dictionary<string, int> outgoingCounts = new(StringComparer.Ordinal);
+
+        foreach (WorkflowNodeDto node in workflow.Graph.Nodes)
+        {
+            if (string.IsNullOrWhiteSpace(node.Id))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.nodes.id",
+                    Message = "Workflow nodes must have an ID.",
+                });
+                continue;
+            }
+
+            if (!nodesById.TryAdd(node.Id, node))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.nodes.id",
+                    NodeId = node.Id,
+                    Message = $"Workflow graph contains duplicate node \"{node.Id}\".",
+                });
+                continue;
+            }
+
+            if (!ExecutableNodeKinds.Contains(node.Kind))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.nodes.kind",
+                    NodeId = node.Id,
+                    Message = $"Workflow node kind \"{node.Kind}\" is not executable yet.",
+                });
+            }
+
+            if (string.Equals(node.Kind, "agent", StringComparison.OrdinalIgnoreCase))
+            {
+                if (string.IsNullOrWhiteSpace(node.Config.Name))
+                {
+                    issues.Add(new WorkflowValidationIssueDto
+                    {
+                        Field = "graph.nodes.config.name",
+                        NodeId = node.Id,
+                        Message = "Agent nodes require a name.",
+                    });
+                }
+
+                if (string.IsNullOrWhiteSpace(node.Config.Model))
+                {
+                    issues.Add(new WorkflowValidationIssueDto
+                    {
+                        Field = "graph.nodes.config.model",
+                        NodeId = node.Id,
+                        Message = $"Agent node \"{node.Label}\" requires a model.",
+                    });
+                }
+            }
+        }
+
+        foreach (WorkflowEdgeDto edge in workflow.Graph.Edges)
+        {
+            if (string.IsNullOrWhiteSpace(edge.Id))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges.id",
+                    Message = "Workflow edges must have an ID.",
+                });
+                continue;
+            }
+
+            if (!edgeIds.Add(edge.Id))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges.id",
+                    EdgeId = edge.Id,
+                    Message = $"Workflow graph contains duplicate edge \"{edge.Id}\".",
+                });
+            }
+
+            if (!nodesById.ContainsKey(edge.Source) || !nodesById.ContainsKey(edge.Target))
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges",
+                    EdgeId = edge.Id,
+                    Message = $"Workflow edge \"{edge.Id}\" must connect known nodes.",
+                });
+                continue;
+            }
+
+            outgoingCounts[edge.Source] = outgoingCounts.TryGetValue(edge.Source, out int outgoing)
+                ? outgoing + 1
+                : 1;
+            incomingCounts[edge.Target] = incomingCounts.TryGetValue(edge.Target, out int incoming)
+                ? incoming + 1
+                : 1;
+        }
+
+        List<WorkflowNodeDto> startNodes = workflow.Graph.Nodes
+            .Where(node => string.Equals(node.Kind, "start", StringComparison.OrdinalIgnoreCase))
+            .ToList();
+        List<WorkflowNodeDto> endNodes = workflow.Graph.Nodes
+            .Where(node => string.Equals(node.Kind, "end", StringComparison.OrdinalIgnoreCase))
+            .ToList();
+        List<WorkflowNodeDto> agentNodes = workflow.Graph.Nodes
+            .Where(node => string.Equals(node.Kind, "agent", StringComparison.OrdinalIgnoreCase))
+            .ToList();
+
+        if (startNodes.Count != 1)
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "graph.nodes",
+                Message = "Workflow graphs must contain exactly one start node.",
+            });
+        }
+
+        if (endNodes.Count != 1)
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "graph.nodes",
+                Message = "Workflow graphs must contain exactly one end node.",
+            });
+        }
+
+        if (agentNodes.Count == 0)
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "graph.nodes",
+                Message = "Workflow graphs must contain at least one agent node.",
+            });
+        }
+
+        foreach (WorkflowNodeDto startNode in startNodes)
+        {
+            if (incomingCounts.GetValueOrDefault(startNode.Id) != 0)
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges",
+                    NodeId = startNode.Id,
+                    Message = "Start nodes cannot have incoming edges.",
+                });
+            }
+
+            if (outgoingCounts.GetValueOrDefault(startNode.Id) == 0)
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges",
+                    NodeId = startNode.Id,
+                    Message = "Start nodes must connect to at least one downstream node.",
+                });
+            }
+        }
+
+        foreach (WorkflowNodeDto endNode in endNodes)
+        {
+            if (outgoingCounts.GetValueOrDefault(endNode.Id) != 0)
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges",
+                    NodeId = endNode.Id,
+                    Message = "End nodes cannot have outgoing edges.",
+                });
+            }
+        }
+
+        foreach (IGrouping<string, WorkflowEdgeDto> fanOutGroup in workflow.Graph.Edges
+                     .Where(edge => string.Equals(edge.Kind, "fan-out", StringComparison.OrdinalIgnoreCase))
+                     .GroupBy(edge => edge.Source, StringComparer.Ordinal))
+        {
+            if (fanOutGroup.Count() < 2)
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges.kind",
+                    NodeId = fanOutGroup.Key,
+                    Message = "Fan-out edges require at least two outgoing fan-out connections from the same source.",
+                });
+            }
+        }
+
+        foreach (IGrouping<string, WorkflowEdgeDto> fanInGroup in workflow.Graph.Edges
+                     .Where(edge => string.Equals(edge.Kind, "fan-in", StringComparison.OrdinalIgnoreCase))
+                     .GroupBy(edge => edge.Target, StringComparer.Ordinal))
+        {
+            if (fanInGroup.Count() < 2)
+            {
+                issues.Add(new WorkflowValidationIssueDto
+                {
+                    Field = "graph.edges.kind",
+                    NodeId = fanInGroup.Key,
+                    Message = "Fan-in edges require at least two incoming fan-in connections to the same target.",
+                });
+            }
+        }
+
+        WorkflowNodeDto? start = startNodes.FirstOrDefault();
+        if (start is not null && endNodes.Count > 0 && !HasPathToAnyEnd(start.Id, workflow.Graph, endNodes.Select(node => node.Id)))
+        {
+            issues.Add(new WorkflowValidationIssueDto
+            {
+                Field = "graph.edges",
+                Message = "Workflow graph must include a path from the start node to at least one end node.",
+            });
+        }
+
+        return issues;
+    }
+
+    private static bool HasPathToAnyEnd(
+        string startNodeId,
+        WorkflowGraphDto graph,
+        IEnumerable<string> endNodeIds)
+    {
+        HashSet<string> endSet = endNodeIds.ToHashSet(StringComparer.Ordinal);
+        Dictionary<string, List<string>> outgoing = graph.Edges
+            .GroupBy(edge => edge.Source, StringComparer.Ordinal)
+            .ToDictionary(
+                group => group.Key,
+                group => group.Select(edge => edge.Target).ToList(),
+                StringComparer.Ordinal);
+
+        Queue<string> queue = new([startNodeId]);
+        HashSet<string> visited = new(StringComparer.Ordinal);
+        while (queue.Count > 0)
+        {
+            string current = queue.Dequeue();
+            if (!visited.Add(current))
+            {
+                continue;
+            }
+
+            if (endSet.Contains(current))
+            {
+                return true;
+            }
+
+            foreach (string target in outgoing.GetValueOrDefault(current, []))
+            {
+                queue.Enqueue(target);
+            }
+        }
+
+        return false;
+    }
+}

sidecar/tests/Aryx.AgentHost.Tests/Aryx.AgentHost.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>

sidecar/tests/Aryx.AgentHost.Tests/SidecarProtocolHostTests.cs

@@ -108,6 +108,76 @@ public sealed class SidecarProtocolHostTests
             });
     }
 
+    [Fact]
+    public async Task ValidateWorkflowCommand_ReturnsIssuesAndCompletion()
+    {
+        IReadOnlyList<JsonElement> events = await RunHostAsync(new ValidateWorkflowCommandDto
+        {
+            Type = "validate-workflow",
+            RequestId = "validate-workflow-1",
+            Workflow = new WorkflowDefinitionDto
+            {
+                Id = "workflow-1",
+                Name = "",
+                Graph = new WorkflowGraphDto
+                {
+                    Nodes =
+                    [
+                        new WorkflowNodeDto
+                        {
+                            Id = "start",
+                            Kind = "start",
+                            Label = "Start",
+                            Config = new WorkflowNodeConfigDto { Kind = "start" },
+                        },
+                        new WorkflowNodeDto
+                        {
+                            Id = "end",
+                            Kind = "end",
+                            Label = "End",
+                            Config = new WorkflowNodeConfigDto { Kind = "end" },
+                        },
+                    ],
+                    Edges =
+                    [
+                        new WorkflowEdgeDto
+                        {
+                            Id = "edge-start-end",
+                            Source = "start",
+                            Target = "end",
+                            Kind = "direct",
+                        },
+                    ],
+                },
+                Settings = new WorkflowSettingsDto
+                {
+                    Checkpointing = new WorkflowCheckpointSettingsDto(),
+                },
+            },
+        });
+
+        Assert.Collection(
+            events,
+            validationEvent =>
+            {
+                Assert.Equal("workflow-validation", validationEvent.GetProperty("type").GetString());
+                Assert.Equal("validate-workflow-1", validationEvent.GetProperty("requestId").GetString());
+
+                JsonElement[] issues = validationEvent.GetProperty("issues").EnumerateArray().ToArray();
+                Assert.Contains(issues, issue =>
+                    issue.GetProperty("field").GetString() == "name"
+                    && issue.GetProperty("message").GetString() == "Workflow name is required.");
+                Assert.Contains(issues, issue =>
+                    issue.GetProperty("field").GetString() == "graph.nodes"
+                    && issue.GetProperty("message").GetString() == "Workflow graphs must contain at least one agent node.");
+            },
+            completionEvent =>
+            {
+                Assert.Equal("command-complete", completionEvent.GetProperty("type").GetString());
+                Assert.Equal("validate-workflow-1", completionEvent.GetProperty("requestId").GetString());
+            });
+    }
+
     [Fact]
     public async Task RunTurnCommand_ReturnsActivityEventsAndCompletion()
     {

src/main/AryxAppService.ts

@@ -36,6 +36,12 @@ import {
   type ReasoningEffort,
   validatePatternDefinition,
 } from '@shared/domain/pattern';
+import {
+  buildWorkflowExecutionPattern,
+  normalizeWorkflowDefinition,
+  validateWorkflowDefinition,
+  type WorkflowDefinition,
+} from '@shared/domain/workflow';
 import {
   normalizeWorkspaceAgentDefinition,
   resolvePatternAgents,
@@ -623,6 +629,32 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     return this.persistAndBroadcast(workspace);
   }
 
+  async saveWorkflow(workflow: WorkflowDefinition): Promise<WorkspaceState> {
+    const workspace = await this.loadWorkspace();
+    const normalizedWorkflow = normalizeWorkflowDefinition(workflow);
+    const issues = validateWorkflowDefinition(normalizedWorkflow).filter((issue) => issue.level === 'error');
+    if (issues.length > 0) {
+      throw new Error(issues[0].message);
+    }
+
+    const existingIndex = workspace.workflows.findIndex((current) => current.id === workflow.id);
+    const candidate: WorkflowDefinition = {
+      ...normalizedWorkflow,
+      isFavorite: workflow.isFavorite ?? workspace.workflows[existingIndex]?.isFavorite,
+      createdAt: existingIndex >= 0 ? workspace.workflows[existingIndex].createdAt : nowIso(),
+      updatedAt: nowIso(),
+    };
+
+    if (existingIndex >= 0) {
+      workspace.workflows[existingIndex] = candidate;
+    } else {
+      workspace.workflows.push(candidate);
+    }
+
+    workspace.selectedWorkflowId = candidate.id;
+    return this.persistAndBroadcast(workspace);
+  }
+
   async setPatternFavorite(patternId: string, isFavorite: boolean): Promise<WorkspaceState> {
     const workspace = await this.loadWorkspace();
     const pattern = this.requirePattern(workspace, patternId);
@@ -726,6 +758,17 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     return this.persistAndBroadcast(workspace);
   }
 
+  async deleteWorkflow(workflowId: string): Promise<WorkspaceState> {
+    const workspace = await this.loadWorkspace();
+    workspace.workflows = workspace.workflows.filter((workflow) => workflow.id !== workflowId);
+
+    if (workspace.selectedWorkflowId === workflowId) {
+      workspace.selectedWorkflowId = workspace.workflows[0]?.id;
+    }
+
+    return this.persistAndBroadcast(workspace);
+  }
+
   async saveMcpServer(server: McpServerDefinition): Promise<WorkspaceState> {
     const workspace = await this.loadWorkspace();
     const existingIndex = workspace.settings.tooling.mcpServers.findIndex(
@@ -881,6 +924,41 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     workspace.sessions.unshift(session);
     workspace.selectedProjectId = project.id;
     workspace.selectedPatternId = pattern.id;
+    workspace.selectedWorkflowId = undefined;
+    workspace.selectedSessionId = session.id;
+    return this.persistAndBroadcast(workspace);
+  }
+
+  async createWorkflowSession(projectId: string, workflowId: string): Promise<WorkspaceState> {
+    const workspace = await this.loadWorkspace();
+    const project = this.requireProject(workspace, projectId);
+    const workflow = this.requireWorkflow(workspace, workflowId);
+    const modelCatalog = await this.loadAvailableModelCatalog();
+    const executionPattern = normalizePatternModels(buildWorkflowExecutionPattern(workflow), modelCatalog);
+
+    const session: SessionRecord = {
+      id: createId('session'),
+      projectId: project.id,
+      patternId: workflow.id,
+      workflowId: workflow.id,
+      title: workflow.name,
+      titleSource: 'auto',
+      createdAt: nowIso(),
+      updatedAt: nowIso(),
+      status: 'idle',
+      messages: [],
+      sessionModelConfig: executionPattern.agents.length === 1
+        ? createSessionModelConfig(executionPattern)
+        : undefined,
+      tooling: createSessionToolingSelection(),
+      runs: [],
+    };
+
+    await this.ensureScratchpadSessionDirectory(session);
+    workspace.sessions.unshift(session);
+    workspace.selectedProjectId = project.id;
+    workspace.selectedPatternId = undefined;
+    workspace.selectedWorkflowId = workflow.id;
     workspace.selectedSessionId = session.id;
     return this.persistAndBroadcast(workspace);
   }
@@ -993,7 +1071,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     }
 
     const project = this.requireProject(workspace, session.projectId);
-    const pattern = this.requirePattern(workspace, session.patternId);
+    const { pattern, workflow } = this.resolveSessionExecutionDefinition(workspace, session);
     const effectivePattern = this.applyProjectCustomizationToPattern(
       await this.buildEffectivePattern(pattern, session, workspace.settings.agents ?? []),
       project,
@@ -1022,11 +1100,19 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
       throw new Error('Regenerated session is missing the user message needed to replay the turn.');
     }
 
-    await this.runPreparedSessionTurn(workspace, regeneratedSession, project, effectivePattern, projectInstructions, {
-      occurredAt,
-      requestId: createId('turn'),
-      triggerMessageId: triggerMessage.id,
-    });
+    await this.runPreparedSessionTurn(
+      workspace,
+      regeneratedSession,
+      project,
+      effectivePattern,
+      projectInstructions,
+      {
+        occurredAt,
+        requestId: createId('turn'),
+        triggerMessageId: triggerMessage.id,
+      },
+      workflow,
+    );
   }
 
   async editAndResendSessionMessage(
@@ -1052,7 +1138,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     }
 
     const project = this.requireProject(workspace, session.projectId);
-    const pattern = this.requirePattern(workspace, session.patternId);
+    const { pattern, workflow } = this.resolveSessionExecutionDefinition(workspace, session);
     const effectivePattern = this.applyProjectCustomizationToPattern(
       await this.buildEffectivePattern(pattern, session, workspace.settings.agents ?? []),
       project,
@@ -1084,11 +1170,19 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
       throw new Error('Edited session is missing the user message needed to replay the turn.');
     }
 
-    await this.runPreparedSessionTurn(workspace, editedSession, project, effectivePattern, projectInstructions, {
-      occurredAt,
-      requestId: createId('turn'),
-      triggerMessageId: triggerMessage.id,
-    });
+    await this.runPreparedSessionTurn(
+      workspace,
+      editedSession,
+      project,
+      effectivePattern,
+      projectInstructions,
+      {
+        occurredAt,
+        requestId: createId('turn'),
+        triggerMessageId: triggerMessage.id,
+      },
+      workflow,
+    );
   }
 
   async sendSessionMessage(
@@ -1106,7 +1200,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
       throw new Error('Wait for the current response or approval checkpoint to finish before sending another message.');
     }
     const project = this.requireProject(workspace, session.projectId);
-    const pattern = this.requirePattern(workspace, session.patternId);
+    const { pattern, workflow } = this.resolveSessionExecutionDefinition(workspace, session);
     const effectivePattern = this.applyProjectCustomizationToPattern(
       await this.buildEffectivePattern(pattern, session, workspace.settings.agents ?? []),
       project,
@@ -1135,13 +1229,21 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
       attachments: attachments?.length ? attachments : undefined,
       promptInvocation: normalizedPromptInvocation,
     });
-    await this.runPreparedSessionTurn(workspace, session, project, effectivePattern, projectInstructions, {
-      occurredAt,
-      requestId,
-      triggerMessageId: userMessageId,
-      messageMode,
-      attachments,
-    });
+    await this.runPreparedSessionTurn(
+      workspace,
+      session,
+      project,
+      effectivePattern,
+      projectInstructions,
+      {
+        occurredAt,
+        requestId,
+        triggerMessageId: userMessageId,
+        messageMode,
+        attachments,
+      },
+      workflow,
+    );
   }
 
   async cancelSessionTurn(sessionId: string): Promise<void> {
@@ -1328,7 +1430,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     const session = this.requireSession(workspace, sessionId);
     const project = this.requireProject(workspace, session.projectId);
     const modelCatalog = await this.loadAvailableModelCatalog();
-    const pattern = this.requirePattern(workspace, session.patternId);
+    const { pattern } = this.resolveSessionExecutionDefinition(workspace, session);
     const effectivePattern = normalizePatternModels(pattern, modelCatalog);
 
     if (effectivePattern.agents.length !== 1) {
@@ -1497,6 +1599,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
       messageMode?: MessageMode;
       attachments?: ChatMessageAttachment[];
     },
+    effectiveWorkflow?: WorkflowDefinition,
   ): Promise<void> {
     const workspaceKind = isScratchpadProject(project) ? 'scratchpad' : 'project';
     const { occurredAt, requestId, triggerMessageId, messageMode, attachments } = options;
@@ -1529,6 +1632,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
         workingDirectory: runWorkingDirectory,
         workspaceKind,
         pattern: patternForTurn,
+        workflow: effectiveWorkflow ? { id: effectiveWorkflow.id, name: effectiveWorkflow.name } : undefined,
         triggerMessageId,
         startedAt: occurredAt,
         preRunGitSnapshot,
@@ -1558,6 +1662,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
         messageMode,
         projectInstructions,
         pattern: patternForTurn,
+        workflow: effectiveWorkflow,
         messages: session.messages,
         attachments: attachments?.length ? attachments : undefined,
         promptInvocation,
@@ -2126,6 +2231,32 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     return pattern;
   }
 
+  private requireWorkflow(workspace: WorkspaceState, workflowId: string): WorkflowDefinition {
+    const workflow = workspace.workflows.find((current) => current.id === workflowId);
+    if (!workflow) {
+      throw new Error(`Workflow "${workflowId}" was not found.`);
+    }
+
+    return workflow;
+  }
+
+  private resolveSessionExecutionDefinition(
+    workspace: WorkspaceState,
+    session: SessionRecord,
+  ): { pattern: PatternDefinition; workflow?: WorkflowDefinition } {
+    if (session.workflowId) {
+      const workflow = this.requireWorkflow(workspace, session.workflowId);
+      return {
+        workflow,
+        pattern: buildWorkflowExecutionPattern(workflow),
+      };
+    }
+
+    return {
+      pattern: this.requirePattern(workspace, session.patternId),
+    };
+  }
+
   private requireSession(workspace: WorkspaceState, sessionId: string): SessionRecord {
     const session = workspace.sessions.find((current) => current.id === sessionId);
     if (!session) {
@@ -2335,7 +2466,7 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     messages: ChatMessageRecord[],
   ): void {
     const session = this.requireSession(workspace, sessionId);
-    const pattern = this.requirePattern(workspace, session.patternId);
+    const { pattern } = this.resolveSessionExecutionDefinition(workspace, session);
     const incomingIds = new Set(messages.map((message) => message.id));
 
     // Messages that were streamed during the turn already exist in session.messages

src/main/ipc/registerIpcHandlers.ts

@@ -6,6 +6,7 @@ import type {
   BranchSessionInput,
   CancelSessionTurnInput,
   CreateSessionInput,
+  CreateWorkflowSessionInput,
   CreateProjectGitBranchInput,
   DismissSessionMcpAuthInput,
   DismissSessionPlanReviewInput,
@@ -34,6 +35,7 @@ import type {
   SaveLspProfileInput,
   SaveMcpServerInput,
   SavePatternInput,
+  SaveWorkflowInput,
   SaveWorkspaceAgentInput,
   SendSessionMessageInput,
   SetPatternFavoriteInput,
@@ -112,6 +114,8 @@ export function registerIpcHandlers(
   ipcMain.handle(ipcChannels.setPatternFavorite, (_event, input: SetPatternFavoriteInput) =>
     service.setPatternFavorite(input.patternId, input.isFavorite),
   );
+  ipcMain.handle(ipcChannels.saveWorkflow, (_event, input: SaveWorkflowInput) => service.saveWorkflow(input.workflow));
+  ipcMain.handle(ipcChannels.deleteWorkflow, (_event, workflowId: string) => service.deleteWorkflow(workflowId));
   ipcMain.handle(ipcChannels.setTheme, async (_event, theme: AppearanceTheme) => {
     const result = await service.setTheme(theme);
     applyTitleBarTheme(window, theme);
@@ -180,6 +184,9 @@ export function registerIpcHandlers(
   ipcMain.handle(ipcChannels.createSession, (_event, input: CreateSessionInput) =>
     service.createSession(input.projectId, input.patternId),
   );
+  ipcMain.handle(ipcChannels.createWorkflowSession, (_event, input: CreateWorkflowSessionInput) =>
+    service.createWorkflowSession(input.projectId, input.workflowId),
+  );
   ipcMain.handle(ipcChannels.duplicateSession, (_event, input: DuplicateSessionInput) =>
     service.duplicateSession(input.sessionId),
   );

src/main/persistence/workspaceRepository.ts

@@ -15,6 +15,7 @@ import {
   normalizeSessionToolingSelection,
   normalizeWorkspaceSettings,
 } from '@shared/domain/tooling';
+import { normalizeWorkflowDefinition } from '@shared/domain/workflow';
 import {
   applyDefaultToolApprovalPolicy,
   normalizePendingApprovalState,
@@ -120,6 +121,7 @@ export class WorkspaceRepository {
         approvalPolicy: applyDefaultToolApprovalPolicy(pattern.approvalPolicy),
         graph: resolvePatternGraph(pattern),
       })),
+      workflows: (stored.workflows ?? []).map(normalizeWorkflowDefinition),
       projects,
       sessions,
       settings,

src/main/sidecar/sidecarProcess.ts

@@ -14,6 +14,7 @@ import type {
   McpOauthRequiredEvent,
   ExitPlanModeRequestedEvent,
   ValidatePatternCommand,
+  ValidateWorkflowCommand,
   RunTurnCommand,
   CopilotSessionListFilter,
   CopilotSessionInfo,
@@ -46,6 +47,12 @@ type PendingCommand =
       resolve: (issues: ValidatePatternCommand['pattern'] extends never ? never : unknown) => void;
       reject: (error: Error) => void;
     })
+  | ({
+      processId: number;
+      kind: 'validate-workflow';
+      resolve: (issues: ValidateWorkflowCommand['workflow'] extends never ? never : unknown) => void;
+      reject: (error: Error) => void;
+    })
   | ({
       processId: number;
       kind: 'resolve-approval';
@@ -127,6 +134,14 @@ export class SidecarClient {
     });
   }
 
+  async validateWorkflow(workflow: ValidateWorkflowCommand['workflow']): Promise<unknown> {
+    return this.dispatch<unknown>({
+      type: 'validate-workflow',
+      requestId: `validate-workflow-${Date.now()}`,
+      workflow,
+    });
+  }
+
   async runTurn(
     command: RunTurnCommand,
     onDelta: (event: TurnDeltaEvent) => void | Promise<void>,
@@ -317,6 +332,13 @@ export class SidecarClient {
           resolve: resolve as (issues: unknown) => void,
           reject,
         });
+      } else if (command.type === 'validate-workflow') {
+        this.pending.set(command.requestId, {
+          processId: state.id,
+          kind: 'validate-workflow',
+          resolve: resolve as (issues: unknown) => void,
+          reject,
+        });
       } else if (command.type === 'resolve-approval') {
         this.pending.set(command.requestId, {
           processId: state.id,
@@ -413,6 +435,12 @@ export class SidecarClient {
           this.pending.delete(event.requestId);
         }
         return;
+      case 'workflow-validation':
+        if (pending.kind === 'validate-workflow') {
+          pending.resolve(event.issues);
+          this.pending.delete(event.requestId);
+        }
+        return;
       case 'turn-delta':
         if (pending.kind === 'run-turn' && shouldHandleRunTurnEvent(pending)) {
           this.invokeRunTurnHandler(event.requestId, pending, () => pending.onDelta(event));

src/preload/index.ts

@@ -26,6 +26,9 @@ const api: ElectronApi = {
   savePattern: (input) => ipcRenderer.invoke(ipcChannels.savePattern, input),
   deletePattern: (patternId) => ipcRenderer.invoke(ipcChannels.deletePattern, patternId),
   setPatternFavorite: (input) => ipcRenderer.invoke(ipcChannels.setPatternFavorite, input),
+  saveWorkflow: (input) => ipcRenderer.invoke(ipcChannels.saveWorkflow, input),
+  deleteWorkflow: (workflowId) => ipcRenderer.invoke(ipcChannels.deleteWorkflow, workflowId),
+  createWorkflowSession: (input) => ipcRenderer.invoke(ipcChannels.createWorkflowSession, input),
   setTheme: (theme) => ipcRenderer.invoke(ipcChannels.setTheme, theme),
   setTerminalHeight: (input) => ipcRenderer.invoke(ipcChannels.setTerminalHeight, input),
   setNotificationsEnabled: (enabled) => ipcRenderer.invoke(ipcChannels.setNotificationsEnabled, enabled),

src/shared/contracts/channels.ts

@@ -15,6 +15,9 @@ export const ipcChannels = {
   savePattern: 'patterns:save',
   deletePattern: 'patterns:delete',
   setPatternFavorite: 'patterns:set-favorite',
+  saveWorkflow: 'workflows:save',
+  deleteWorkflow: 'workflows:delete',
+  createWorkflowSession: 'workflows:create-session',
   setTheme: 'settings:set-theme',
   setTerminalHeight: 'settings:set-terminal-height',
   setNotificationsEnabled: 'settings:set-notifications-enabled',

src/shared/contracts/ipc.ts

@@ -1,6 +1,7 @@
 import type { ApprovalDecision } from '@shared/domain/approval';
 import type { SidecarCapabilities, InteractionMode, MessageMode, QuotaSnapshot } from '@shared/contracts/sidecar';
 import type { PatternDefinition, ReasoningEffort } from '@shared/domain/pattern';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import type {
   ProjectGitBranchSummary,
   ProjectGitCommitMessageSuggestion,
@@ -28,10 +29,19 @@ export interface CreateSessionInput {
   patternId: string;
 }
 
+export interface CreateWorkflowSessionInput {
+  projectId: string;
+  workflowId: string;
+}
+
 export interface SavePatternInput {
   pattern: PatternDefinition;
 }
 
+export interface SaveWorkflowInput {
+  workflow: WorkflowDefinition;
+}
+
 export interface SendSessionMessageInput {
   sessionId: string;
   content: string;
@@ -274,6 +284,8 @@ export interface ElectronApi {
   setProjectAgentProfileEnabled(input: SetProjectAgentProfileEnabledInput): Promise<WorkspaceState>;
   savePattern(input: SavePatternInput): Promise<WorkspaceState>;
   deletePattern(patternId: string): Promise<WorkspaceState>;
+  saveWorkflow(input: SaveWorkflowInput): Promise<WorkspaceState>;
+  deleteWorkflow(workflowId: string): Promise<WorkspaceState>;
   saveMcpServer(input: SaveMcpServerInput): Promise<WorkspaceState>;
   deleteMcpServer(serverId: string): Promise<WorkspaceState>;
   saveLspProfile(input: SaveLspProfileInput): Promise<WorkspaceState>;
@@ -283,6 +295,7 @@ export interface ElectronApi {
   updateSessionTooling(input: UpdateSessionToolingInput): Promise<WorkspaceState>;
   updateSessionApprovalSettings(input: UpdateSessionApprovalSettingsInput): Promise<WorkspaceState>;
   createSession(input: CreateSessionInput): Promise<WorkspaceState>;
+  createWorkflowSession(input: CreateWorkflowSessionInput): Promise<WorkspaceState>;
   duplicateSession(input: DuplicateSessionInput): Promise<WorkspaceState>;
   branchSession(input: BranchSessionInput): Promise<WorkspaceState>;
   setSessionMessagePinned(input: SetSessionMessagePinnedInput): Promise<WorkspaceState>;

src/shared/contracts/sidecar.ts

@@ -4,6 +4,7 @@ import type { ChatMessageRecord } from '@shared/domain/session';
 import type { RuntimeToolDefinition } from '@shared/domain/tooling';
 import type { ChatMessageAttachment } from '@shared/domain/attachment';
 import type { ProjectPromptInvocation } from '@shared/domain/projectCustomization';
+import type { WorkflowDefinition, WorkflowValidationIssue } from '@shared/domain/workflow';
 
 export interface SidecarModeCapability {
   available: boolean;
@@ -70,6 +71,12 @@ export interface ValidatePatternCommand {
   pattern: PatternDefinition;
 }
 
+export interface ValidateWorkflowCommand {
+  type: 'validate-workflow';
+  requestId: string;
+  workflow: WorkflowDefinition;
+}
+
 export type InteractionMode = 'interactive' | 'plan';
 export type MessageMode = 'enqueue' | 'immediate';
 
@@ -89,6 +96,7 @@ export interface RunTurnCommand {
   messageMode?: MessageMode;
   projectInstructions?: string;
   pattern: PatternDefinition;
+  workflow?: WorkflowDefinition;
   messages: ChatMessageRecord[];
   attachments?: ChatMessageAttachment[];
   promptInvocation?: ProjectPromptInvocation;
@@ -147,6 +155,7 @@ export interface CopilotSessionListFilter {
 export type SidecarCommand =
   | DescribeCapabilitiesCommand
   | ValidatePatternCommand
+  | ValidateWorkflowCommand
   | RunTurnCommand
   | CancelTurnCommand
   | ResolveApprovalCommand
@@ -230,6 +239,12 @@ export interface PatternValidationEvent {
   issues: PatternValidationIssue[];
 }
 
+export interface WorkflowValidationEvent {
+  type: 'workflow-validation';
+  requestId: string;
+  issues: WorkflowValidationIssue[];
+}
+
 export interface TurnDeltaEvent {
   type: 'turn-delta';
   requestId: string;
@@ -592,6 +607,7 @@ export interface CommandCompleteEvent {
 export type SidecarEvent =
   | CapabilitiesEvent
   | PatternValidationEvent
+  | WorkflowValidationEvent
   | TurnDeltaEvent
   | TurnCompleteEvent
   | MessageReclassifiedEvent

src/shared/domain/runTimeline.ts

@@ -17,6 +17,7 @@ import type {
   ProjectGitWorkingTreeSnapshot,
   ProjectRecord,
 } from '@shared/domain/project';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import { createId } from '@shared/utils/ids';
 
 export type SessionRunStatus = 'running' | 'completed' | 'cancelled' | 'error';
@@ -76,6 +77,8 @@ export interface SessionRunRecord {
   patternId: string;
   patternName: string;
   patternMode: PatternDefinition['mode'];
+  workflowId?: string;
+  workflowName?: string;
   triggerMessageId: string;
   startedAt: string;
   completedAt?: string;
@@ -93,6 +96,7 @@ export interface CreateSessionRunRecordInput {
   workingDirectory?: string;
   workspaceKind: SessionRunWorkspaceKind;
   pattern: Pick<PatternDefinition, 'id' | 'name' | 'mode' | 'agents'>;
+  workflow?: Pick<WorkflowDefinition, 'id' | 'name'>;
   triggerMessageId: string;
   startedAt: string;
   preRunGitSnapshot?: ProjectGitWorkingTreeSnapshot;
@@ -610,6 +614,8 @@ export function createSessionRunRecord(input: CreateSessionRunRecordInput): Sess
     patternId: input.pattern.id,
     patternName: input.pattern.name,
     patternMode: input.pattern.mode,
+    workflowId: normalizeOptionalString(input.workflow?.id),
+    workflowName: normalizeOptionalString(input.workflow?.name),
     triggerMessageId: input.triggerMessageId,
     startedAt: input.startedAt,
     status: 'running',
@@ -655,6 +661,8 @@ export function normalizeSessionRunRecords(
     const workingDirectory = normalizeOptionalString(run.workingDirectory);
     const patternId = normalizeOptionalString(run.patternId);
     const patternName = normalizeOptionalString(run.patternName);
+    const workflowId = normalizeOptionalString(run.workflowId);
+    const workflowName = normalizeOptionalString(run.workflowName);
     const triggerMessageId = normalizeOptionalString(run.triggerMessageId);
     const startedAt = normalizeOptionalString(run.startedAt);
     if (!id || !requestId || !projectId || !projectPath || !patternId || !patternName || !triggerMessageId || !startedAt) {
@@ -672,6 +680,8 @@ export function normalizeSessionRunRecords(
         patternId,
         patternName,
         patternMode: run.patternMode,
+        workflowId,
+        workflowName,
         triggerMessageId,
         startedAt,
         completedAt: normalizeOptionalString(run.completedAt),

src/shared/domain/session.ts

@@ -57,6 +57,7 @@ export interface SessionRecord {
   id: string;
   projectId: string;
   patternId: string;
+  workflowId?: string;
   title: string;
   titleSource?: SessionTitleSource;
   createdAt: string;

src/shared/domain/sessionLibrary.ts

@@ -14,6 +14,7 @@ import {
   type SessionStatus,
 } from '@shared/domain/session';
 import type { WorkspaceState } from '@shared/domain/workspace';
+import { buildWorkflowExecutionPattern } from '@shared/domain/workflow';
 
 export type SessionQueryMatchField = 'title' | 'message' | 'project' | 'pattern';
 export type SessionWorkspaceKind = 'project' | 'scratchpad';
@@ -456,6 +457,7 @@ export function listPinnedMessages(workspace: WorkspaceState): PinnedMessageHit[
 export function querySessions(workspace: WorkspaceState, input: QuerySessionsInput): SessionQueryResult[] {
   const projectsById = new Map<string, ProjectRecord>(workspace.projects.map((project) => [project.id, project]));
   const patternsById = new Map<string, PatternDefinition>(workspace.patterns.map((pattern) => [pattern.id, pattern]));
+  const workflowsById = new Map(workspace.workflows.map((workflow) => [workflow.id, workflow]));
   const searchTokens = tokenizeSearchText(input.searchText);
 
   return workspace.sessions
@@ -466,7 +468,17 @@ export function querySessions(workspace: WorkspaceState, input: QuerySessionsInp
       }
 
       const searchMatch = resolveSearchMatch(
-        buildSearchFields(session, projectsById.get(session.projectId), patternsById.get(session.patternId)),
+        buildSearchFields(
+          session,
+          projectsById.get(session.projectId),
+          patternsById.get(session.patternId)
+            ?? (session.workflowId
+              ? (() => {
+                const workflow = workflowsById.get(session.workflowId);
+                return workflow ? buildWorkflowExecutionPattern(workflow) : undefined;
+              })()
+              : undefined),
+        ),
         searchTokens,
       );
       if (!searchMatch) {

src/shared/domain/workflow.ts

@@ -0,0 +1,606 @@
+import type { ApprovalPolicy } from '@shared/domain/approval';
+import {
+  syncPatternGraph,
+  type PatternDefinition,
+  type PatternGraph,
+  type PatternAgentDefinition,
+} from '@shared/domain/pattern';
+
+export type WorkflowNodeKind =
+  | 'start'
+  | 'end'
+  | 'agent'
+  | 'code-executor'
+  | 'function-executor'
+  | 'sub-workflow'
+  | 'request-port';
+
+export type WorkflowEdgeKind = 'direct' | 'fan-out' | 'fan-in';
+export type WorkflowExecutionMode = 'off-thread' | 'lockstep';
+
+export interface WorkflowPosition {
+  x: number;
+  y: number;
+}
+
+export interface WorkflowCheckpointSettings {
+  enabled: boolean;
+}
+
+export interface WorkflowTelemetrySettings {
+  openTelemetry?: boolean;
+  sensitiveData?: boolean;
+}
+
+export interface WorkflowStateScope {
+  name: string;
+  description?: string;
+  initialValues?: Record<string, unknown>;
+}
+
+export interface WorkflowSettings {
+  checkpointing: WorkflowCheckpointSettings;
+  executionMode: WorkflowExecutionMode;
+  maxIterations?: number;
+  approvalPolicy?: ApprovalPolicy;
+  stateScopes?: WorkflowStateScope[];
+  telemetry?: WorkflowTelemetrySettings;
+}
+
+export interface StartNodeConfig {
+  kind: 'start';
+  inputType?: string;
+}
+
+export interface EndNodeConfig {
+  kind: 'end';
+  outputType?: string;
+}
+
+export interface AgentNodeConfig extends PatternAgentDefinition {
+  kind: 'agent';
+}
+
+export interface CodeExecutorConfig {
+  kind: 'code-executor';
+  inputType?: string;
+  outputType?: string;
+  implementation?: string;
+}
+
+export interface FunctionExecutorConfig {
+  kind: 'function-executor';
+  functionRef: string;
+  parameters?: Record<string, unknown>;
+}
+
+export interface SubWorkflowConfig {
+  kind: 'sub-workflow';
+  workflowId?: string;
+  inlineWorkflow?: WorkflowDefinition;
+}
+
+export interface RequestPortConfig {
+  kind: 'request-port';
+  portId: string;
+  requestType: string;
+  responseType: string;
+  prompt?: string;
+}
+
+export type WorkflowNodeConfig =
+  | StartNodeConfig
+  | EndNodeConfig
+  | AgentNodeConfig
+  | CodeExecutorConfig
+  | FunctionExecutorConfig
+  | SubWorkflowConfig
+  | RequestPortConfig;
+
+export interface WorkflowNode {
+  id: string;
+  kind: WorkflowNodeKind;
+  label: string;
+  position: WorkflowPosition;
+  order?: number;
+  config: WorkflowNodeConfig;
+}
+
+export interface WorkflowConditionRule {
+  propertyPath: string;
+  operator: 'equals' | 'not-equals' | 'contains' | 'gt' | 'lt' | 'regex';
+  value: string;
+}
+
+export type EdgeCondition =
+  | { type: 'always' }
+  | { type: 'message-type'; typeName: string }
+  | { type: 'expression'; expression: string }
+  | { type: 'property'; combinator?: 'and' | 'or'; rules: WorkflowConditionRule[] };
+
+export interface FanOutConfig {
+  strategy: 'broadcast' | 'partition';
+  partitionExpression?: string;
+}
+
+export interface WorkflowEdge {
+  id: string;
+  source: string;
+  target: string;
+  kind: WorkflowEdgeKind;
+  condition?: EdgeCondition;
+  label?: string;
+  fanOutConfig?: FanOutConfig;
+}
+
+export interface WorkflowGraph {
+  nodes: WorkflowNode[];
+  edges: WorkflowEdge[];
+}
+
+export interface WorkflowDefinition {
+  id: string;
+  name: string;
+  description: string;
+  isFavorite?: boolean;
+  graph: WorkflowGraph;
+  settings: WorkflowSettings;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface WorkflowValidationIssue {
+  level: 'error' | 'warning';
+  field?: string;
+  message: string;
+  nodeId?: string;
+  edgeId?: string;
+}
+
+const executableNodeKinds = new Set<WorkflowNodeKind>(['start', 'end', 'agent']);
+
+function normalizeOptionalString(value?: string): string | undefined {
+  const trimmed = value?.trim();
+  return trimmed ? trimmed : undefined;
+}
+
+function normalizePosition(position?: Partial<WorkflowPosition>): WorkflowPosition {
+  return {
+    x: typeof position?.x === 'number' && Number.isFinite(position.x) ? position.x : 0,
+    y: typeof position?.y === 'number' && Number.isFinite(position.y) ? position.y : 0,
+  };
+}
+
+function normalizeNodeConfig(kind: WorkflowNodeKind, config?: Partial<WorkflowNodeConfig>): WorkflowNodeConfig {
+  switch (kind) {
+    case 'start':
+      return {
+        kind,
+        inputType: normalizeOptionalString((config as Partial<StartNodeConfig> | undefined)?.inputType),
+      };
+    case 'end':
+      return {
+        kind,
+        outputType: normalizeOptionalString((config as Partial<EndNodeConfig> | undefined)?.outputType),
+      };
+    case 'agent': {
+      const agent = config as Partial<AgentNodeConfig> | undefined;
+      return {
+        kind,
+        id: normalizeOptionalString(agent?.id) ?? '',
+        name: normalizeOptionalString(agent?.name) ?? '',
+        description: agent?.description?.trim() ?? '',
+        instructions: agent?.instructions?.trim() ?? '',
+        model: normalizeOptionalString(agent?.model) ?? '',
+        reasoningEffort: agent?.reasoningEffort,
+        copilot: agent?.copilot,
+        workspaceAgentId: normalizeOptionalString(agent?.workspaceAgentId),
+        overrides: agent?.overrides,
+      };
+    }
+    case 'code-executor': {
+      const value = config as Partial<CodeExecutorConfig> | undefined;
+      return {
+        kind,
+        inputType: normalizeOptionalString(value?.inputType),
+        outputType: normalizeOptionalString(value?.outputType),
+        implementation: value?.implementation?.trim(),
+      };
+    }
+    case 'function-executor': {
+      const value = config as Partial<FunctionExecutorConfig> | undefined;
+      return {
+        kind,
+        functionRef: normalizeOptionalString(value?.functionRef) ?? '',
+        parameters: value?.parameters,
+      };
+    }
+    case 'sub-workflow': {
+      const value = config as Partial<SubWorkflowConfig> | undefined;
+      return {
+        kind,
+        workflowId: normalizeOptionalString(value?.workflowId),
+        inlineWorkflow: value?.inlineWorkflow ? normalizeWorkflowDefinition(value.inlineWorkflow) : undefined,
+      };
+    }
+    case 'request-port': {
+      const value = config as Partial<RequestPortConfig> | undefined;
+      return {
+        kind,
+        portId: normalizeOptionalString(value?.portId) ?? '',
+        requestType: normalizeOptionalString(value?.requestType) ?? '',
+        responseType: normalizeOptionalString(value?.responseType) ?? '',
+        prompt: value?.prompt?.trim(),
+      };
+    }
+  }
+}
+
+export function normalizeWorkflowDefinition(workflow: WorkflowDefinition): WorkflowDefinition {
+  return {
+    ...workflow,
+    name: workflow.name.trim(),
+    description: workflow.description.trim(),
+    graph: {
+      nodes: (workflow.graph?.nodes ?? []).map((node) => ({
+        ...node,
+        id: node.id.trim(),
+        kind: node.kind,
+        label: node.label.trim(),
+        position: normalizePosition(node.position),
+        config: normalizeNodeConfig(node.kind, node.config),
+      })),
+      edges: (workflow.graph?.edges ?? []).map((edge) => ({
+        ...edge,
+        id: edge.id.trim(),
+        source: edge.source.trim(),
+        target: edge.target.trim(),
+        kind: edge.kind,
+        label: normalizeOptionalString(edge.label),
+      })),
+    },
+    settings: {
+      checkpointing: {
+        enabled: workflow.settings?.checkpointing?.enabled ?? false,
+      },
+      executionMode: workflow.settings?.executionMode === 'lockstep' ? 'lockstep' : 'off-thread',
+      maxIterations:
+        typeof workflow.settings?.maxIterations === 'number' && workflow.settings.maxIterations > 0
+          ? Math.round(workflow.settings.maxIterations)
+          : undefined,
+      approvalPolicy: workflow.settings?.approvalPolicy,
+      stateScopes: workflow.settings?.stateScopes?.map((scope) => ({
+        name: scope.name.trim(),
+        description: normalizeOptionalString(scope.description),
+        initialValues: scope.initialValues,
+      })),
+      telemetry: workflow.settings?.telemetry
+        ? {
+          openTelemetry: workflow.settings.telemetry.openTelemetry ?? false,
+          sensitiveData: workflow.settings.telemetry.sensitiveData ?? false,
+        }
+        : undefined,
+    },
+  };
+}
+
+export function resolveWorkflowAgentNodes(workflow: WorkflowDefinition): WorkflowNode[] {
+  return workflow.graph.nodes
+    .filter((node) => node.kind === 'agent')
+    .slice()
+    .sort((left, right) => {
+      const leftOrder = left.order ?? Number.MAX_SAFE_INTEGER;
+      const rightOrder = right.order ?? Number.MAX_SAFE_INTEGER;
+      if (leftOrder !== rightOrder) {
+        return leftOrder - rightOrder;
+      }
+
+      return left.label.localeCompare(right.label);
+    });
+}
+
+export function resolveWorkflowAgents(workflow: WorkflowDefinition): PatternAgentDefinition[] {
+  return resolveWorkflowAgentNodes(workflow).flatMap((node) => {
+    if (node.config.kind !== 'agent') {
+      return [];
+    }
+
+    return [{
+      id: node.config.id || node.id,
+      name: node.config.name,
+      description: node.config.description,
+      instructions: node.config.instructions,
+      model: node.config.model,
+      reasoningEffort: node.config.reasoningEffort,
+      copilot: node.config.copilot,
+      workspaceAgentId: node.config.workspaceAgentId,
+      overrides: node.config.overrides,
+    }];
+  });
+}
+
+function inferWorkflowPatternMode(workflow: WorkflowDefinition): PatternDefinition['mode'] {
+  const hasFanEdges = workflow.graph.edges.some((edge) => edge.kind !== 'direct');
+  const agentCount = resolveWorkflowAgents(workflow).length;
+  if (hasFanEdges) {
+    return 'concurrent';
+  }
+
+  return agentCount <= 1 ? 'single' : 'sequential';
+}
+
+export function buildWorkflowExecutionPattern(workflow: WorkflowDefinition): PatternDefinition {
+  const agents = resolveWorkflowAgents(workflow);
+  const pattern: PatternDefinition = {
+    id: workflow.id,
+    name: workflow.name,
+    description: workflow.description,
+    mode: inferWorkflowPatternMode(workflow),
+    availability: 'available',
+    maxIterations: workflow.settings.maxIterations ?? 5,
+    approvalPolicy: workflow.settings.approvalPolicy,
+    agents,
+    createdAt: workflow.createdAt,
+    updatedAt: workflow.updatedAt,
+  };
+
+  return {
+    ...pattern,
+    graph: syncPatternGraph(pattern).graph as PatternGraph,
+  };
+}
+
+function addIssue(
+  issues: WorkflowValidationIssue[],
+  issue: WorkflowValidationIssue,
+): void {
+  issues.push(issue);
+}
+
+function hasPathToEnd(startNodeId: string, graph: WorkflowGraph, endNodeIds: Set<string>): boolean {
+  const outgoing = new Map<string, WorkflowEdge[]>();
+  for (const edge of graph.edges) {
+    const current = outgoing.get(edge.source);
+    if (current) {
+      current.push(edge);
+    } else {
+      outgoing.set(edge.source, [edge]);
+    }
+  }
+
+  const queue = [startNodeId];
+  const visited = new Set<string>();
+  while (queue.length > 0) {
+    const nodeId = queue.shift()!;
+    if (!visited.add(nodeId)) {
+      continue;
+    }
+    if (endNodeIds.has(nodeId)) {
+      return true;
+    }
+    for (const edge of outgoing.get(nodeId) ?? []) {
+      queue.push(edge.target);
+    }
+  }
+
+  return false;
+}
+
+export function validateWorkflowDefinition(workflow: WorkflowDefinition): WorkflowValidationIssue[] {
+  const normalized = normalizeWorkflowDefinition(workflow);
+  const issues: WorkflowValidationIssue[] = [];
+
+  if (!normalized.name) {
+    addIssue(issues, { level: 'error', field: 'name', message: 'Workflow name is required.' });
+  }
+
+  if (normalized.graph.nodes.length === 0) {
+    addIssue(issues, { level: 'error', field: 'graph', message: 'Workflow graph must include nodes.' });
+    return issues;
+  }
+
+  const nodesById = new Map<string, WorkflowNode>();
+  const edgeIds = new Set<string>();
+  const incomingCounts = new Map<string, number>();
+  const outgoingCounts = new Map<string, number>();
+
+  for (const node of normalized.graph.nodes) {
+    if (!node.id) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.nodes.id',
+        nodeId: node.id,
+        message: 'Workflow nodes must have an ID.',
+      });
+      continue;
+    }
+
+    if (nodesById.has(node.id)) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.nodes.id',
+        nodeId: node.id,
+        message: `Workflow graph contains duplicate node "${node.id}".`,
+      });
+      continue;
+    }
+
+    nodesById.set(node.id, node);
+
+    if (!node.label) {
+      addIssue(issues, {
+        level: 'warning',
+        field: 'graph.nodes.label',
+        nodeId: node.id,
+        message: 'Workflow nodes should have a label.',
+      });
+    }
+
+    if (!executableNodeKinds.has(node.kind)) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.nodes.kind',
+        nodeId: node.id,
+        message: `Workflow node kind "${node.kind}" is not executable yet.`,
+      });
+    }
+
+    if (node.kind === 'agent' && node.config.kind === 'agent') {
+      if (!node.config.name) {
+        addIssue(issues, {
+          level: 'error',
+          field: 'graph.nodes.config.name',
+          nodeId: node.id,
+          message: 'Agent nodes require a name.',
+        });
+      }
+      if (!node.config.model) {
+        addIssue(issues, {
+          level: 'error',
+          field: 'graph.nodes.config.model',
+          nodeId: node.id,
+          message: `Agent node "${node.label || node.id}" requires a model.`,
+        });
+      }
+    }
+  }
+
+  for (const edge of normalized.graph.edges) {
+    if (!edge.id) {
+      addIssue(issues, { level: 'error', field: 'graph.edges.id', message: 'Workflow edges must have an ID.' });
+      continue;
+    }
+    if (!edgeIds.add(edge.id)) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges.id',
+        edgeId: edge.id,
+        message: `Workflow graph contains duplicate edge "${edge.id}".`,
+      });
+    }
+    if (!nodesById.has(edge.source) || !nodesById.has(edge.target)) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges',
+        edgeId: edge.id,
+        message: `Workflow edge "${edge.id}" must connect known nodes.`,
+      });
+      continue;
+    }
+
+    outgoingCounts.set(edge.source, (outgoingCounts.get(edge.source) ?? 0) + 1);
+    incomingCounts.set(edge.target, (incomingCounts.get(edge.target) ?? 0) + 1);
+  }
+
+  const startNodes = normalized.graph.nodes.filter((node) => node.kind === 'start');
+  const endNodes = normalized.graph.nodes.filter((node) => node.kind === 'end');
+  const agentNodes = normalized.graph.nodes.filter((node) => node.kind === 'agent');
+
+  if (startNodes.length !== 1) {
+    addIssue(issues, {
+      level: 'error',
+      field: 'graph.nodes',
+      message: 'Workflow graphs must contain exactly one start node.',
+    });
+  }
+
+  if (endNodes.length !== 1) {
+    addIssue(issues, {
+      level: 'error',
+      field: 'graph.nodes',
+      message: 'Workflow graphs must contain exactly one end node.',
+    });
+  }
+
+  if (agentNodes.length === 0) {
+    addIssue(issues, {
+      level: 'error',
+      field: 'graph.nodes',
+      message: 'Workflow graphs must contain at least one agent node.',
+    });
+  }
+
+  for (const startNode of startNodes) {
+    if ((incomingCounts.get(startNode.id) ?? 0) !== 0) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges',
+        nodeId: startNode.id,
+        message: 'Start nodes cannot have incoming edges.',
+      });
+    }
+    if ((outgoingCounts.get(startNode.id) ?? 0) === 0) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges',
+        nodeId: startNode.id,
+        message: 'Start nodes must connect to at least one downstream node.',
+      });
+    }
+  }
+
+  for (const endNode of endNodes) {
+    if ((outgoingCounts.get(endNode.id) ?? 0) !== 0) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges',
+        nodeId: endNode.id,
+        message: 'End nodes cannot have outgoing edges.',
+      });
+    }
+  }
+
+  const fanOutBySource = new Map<string, WorkflowEdge[]>();
+  const fanInByTarget = new Map<string, WorkflowEdge[]>();
+  for (const edge of normalized.graph.edges) {
+    if (edge.kind === 'fan-out') {
+      const current = fanOutBySource.get(edge.source);
+      if (current) {
+        current.push(edge);
+      } else {
+        fanOutBySource.set(edge.source, [edge]);
+      }
+    }
+    if (edge.kind === 'fan-in') {
+      const current = fanInByTarget.get(edge.target);
+      if (current) {
+        current.push(edge);
+      } else {
+        fanInByTarget.set(edge.target, [edge]);
+      }
+    }
+  }
+
+  for (const [source, edges] of fanOutBySource.entries()) {
+    if (edges.length < 2) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges.kind',
+        nodeId: source,
+        message: 'Fan-out edges require at least two outgoing fan-out connections from the same source.',
+      });
+    }
+  }
+
+  for (const [target, edges] of fanInByTarget.entries()) {
+    if (edges.length < 2) {
+      addIssue(issues, {
+        level: 'error',
+        field: 'graph.edges.kind',
+        nodeId: target,
+        message: 'Fan-in edges require at least two incoming fan-in connections to the same target.',
+      });
+    }
+  }
+
+  const startNode = startNodes[0];
+  if (startNode && endNodes.length > 0 && !hasPathToEnd(startNode.id, normalized.graph, new Set(endNodes.map((node) => node.id)))) {
+    addIssue(issues, {
+      level: 'error',
+      field: 'graph.edges',
+      message: 'Workflow graph must include a path from the start node to at least one end node.',
+    });
+  }
+
+  return issues;
+}

src/shared/domain/workspace.ts

@@ -3,11 +3,13 @@ import { createBuiltinPatterns } from '@shared/domain/pattern';
 import type { ProjectRecord } from '@shared/domain/project';
 import type { SessionRecord } from '@shared/domain/session';
 import { createWorkspaceSettings, type WorkspaceSettings } from '@shared/domain/tooling';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import { nowIso } from '@shared/utils/ids';
 
 export interface WorkspaceState {
   projects: ProjectRecord[];
   patterns: PatternDefinition[];
+  workflows: WorkflowDefinition[];
   sessions: SessionRecord[];
   settings: WorkspaceSettings;
   /** IDs of built-in patterns the user has deleted. Prevents re-adding on load. */
@@ -16,6 +18,7 @@ export interface WorkspaceState {
   mcpProbingServerIds?: string[];
   selectedProjectId?: string;
   selectedPatternId?: string;
+  selectedWorkflowId?: string;
   selectedSessionId?: string;
   lastUpdatedAt: string;
 }
@@ -25,6 +28,7 @@ export function createWorkspaceSeed(): WorkspaceState {
   return {
     projects: [],
     patterns: createBuiltinPatterns(timestamp),
+    workflows: [],
     sessions: [],
     settings: createWorkspaceSettings(),
     lastUpdatedAt: timestamp,

tests/main/appServiceWorkflow.test.ts

@@ -0,0 +1,115 @@
+import { describe, expect, mock, test } from 'bun:test';
+
+import { buildAvailableModelCatalog } from '@shared/domain/models';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
+import { createWorkspaceSeed, type WorkspaceState } from '@shared/domain/workspace';
+
+mock.module('electron', () => {
+  const electronMock = {
+    app: {
+      isPackaged: false,
+      getAppPath: () => 'C:\\workspace\\personal\\repositories\\aryx',
+      getPath: () => 'C:\\workspace\\personal\\repositories\\aryx\\tests\\fixtures',
+    },
+    dialog: {
+      showOpenDialog: async () => ({ canceled: true, filePaths: [] }),
+    },
+    shell: {
+      openPath: async () => '',
+    },
+  };
+
+  return {
+    ...electronMock,
+    default: electronMock,
+  };
+});
+
+mock.module('keytar', () => ({
+  default: {
+    getPassword: async () => null,
+    setPassword: async () => undefined,
+    deletePassword: async () => false,
+  },
+}));
+
+const { AryxAppService } = await import('@main/AryxAppService');
+
+function createService(workspace: WorkspaceState): InstanceType<typeof AryxAppService> {
+  const service = new AryxAppService();
+  const internals = service as unknown as Record<string, unknown>;
+  internals.loadWorkspace = async () => workspace;
+  internals.persistAndBroadcast = async (nextWorkspace: WorkspaceState) => nextWorkspace;
+  internals.loadAvailableModelCatalog = async () => buildAvailableModelCatalog();
+  return service;
+}
+
+function createWorkflow(): WorkflowDefinition {
+  return {
+    id: 'workflow-test',
+    name: 'Workflow Test',
+    description: 'Simple workflow',
+    createdAt: '2026-04-05T00:00:00.000Z',
+    updatedAt: '2026-04-05T00:00:00.000Z',
+    graph: {
+      nodes: [
+        { id: 'start', kind: 'start', label: 'Start', position: { x: 0, y: 0 }, config: { kind: 'start' } },
+        {
+          id: 'agent-primary',
+          kind: 'agent',
+          label: 'Primary',
+          position: { x: 200, y: 0 },
+          order: 0,
+          config: {
+            kind: 'agent',
+            id: 'agent-primary',
+            name: 'Primary',
+            description: 'Main agent',
+            instructions: 'Help the user',
+            model: 'gpt-5.4',
+          },
+        },
+        { id: 'end', kind: 'end', label: 'End', position: { x: 400, y: 0 }, config: { kind: 'end' } },
+      ],
+      edges: [
+        { id: 'e1', source: 'start', target: 'agent-primary', kind: 'direct' },
+        { id: 'e2', source: 'agent-primary', target: 'end', kind: 'direct' },
+      ],
+    },
+    settings: {
+      checkpointing: { enabled: false },
+      executionMode: 'off-thread',
+    },
+  };
+}
+
+describe('AryxAppService workflow operations', () => {
+  test('saves workflows into workspace state', async () => {
+    const workspace = createWorkspaceSeed();
+    const service = createService(workspace);
+
+    const result = await service.saveWorkflow(createWorkflow());
+
+    expect(result.workflows).toHaveLength(1);
+    expect(result.selectedWorkflowId).toBe('workflow-test');
+  });
+
+  test('creates workflow-backed sessions', async () => {
+    const workspace = createWorkspaceSeed();
+    const project = {
+      id: 'project-1',
+      name: 'Project',
+      path: 'C:\\workspace\\project-1',
+      addedAt: '2026-04-05T00:00:00.000Z',
+    };
+    workspace.projects.push(project);
+    workspace.workflows.push(createWorkflow());
+    const service = createService(workspace);
+
+    const result = await service.createWorkflowSession(project.id, 'workflow-test');
+    const session = result.sessions[0];
+
+    expect(session?.workflowId).toBe('workflow-test');
+    expect(result.selectedWorkflowId).toBe('workflow-test');
+  });
+});

tests/renderer/sessionWorkspace.test.ts

@@ -11,6 +11,7 @@ describe('session workspace helpers', () => {
     return {
       projects: [],
       patterns: [],
+      workflows: [],
       settings: createWorkspaceSettings(),
       sessions: [
         {

tests/shared/sessionLibrary.test.ts

@@ -73,9 +73,10 @@ function createSession(overrides?: Partial<SessionRecord>): SessionRecord {
 }
 
 function createWorkspace(overrides?: Partial<WorkspaceState>): WorkspaceState {
-  return {
+  const workspace: WorkspaceState = {
     projects: [createProject(), createProject({ id: 'project-scratchpad', name: 'Scratchpad', path: 'C:\\scratchpad' })],
     patterns: [createPattern(), createPattern({ id: 'pattern-single-chat', name: '1-on-1 Copilot Chat', mode: 'single' })],
+    workflows: [],
     settings: createWorkspaceSettings(),
     sessions: [
       createSession(),
@@ -112,6 +113,11 @@ function createWorkspace(overrides?: Partial<WorkspaceState>): WorkspaceState {
     lastUpdatedAt: '2026-03-23T00:10:00.000Z',
     ...overrides,
   };
+
+  return {
+    ...workspace,
+    workflows: overrides?.workflows ?? workspace.workflows,
+  };
 }
 
 describe('session library helpers', () => {

tests/shared/workflow.test.ts

@@ -0,0 +1,95 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  buildWorkflowExecutionPattern,
+  validateWorkflowDefinition,
+  type WorkflowDefinition,
+} from '@shared/domain/workflow';
+
+const TIMESTAMP = '2026-04-05T00:00:00.000Z';
+
+function createWorkflow(): WorkflowDefinition {
+  return {
+    id: 'workflow-1',
+    name: 'Agent Workflow',
+    description: 'A simple workflow.',
+    createdAt: TIMESTAMP,
+    updatedAt: TIMESTAMP,
+    graph: {
+      nodes: [
+        {
+          id: 'start',
+          kind: 'start',
+          label: 'Start',
+          position: { x: 0, y: 0 },
+          config: { kind: 'start' },
+        },
+        {
+          id: 'agent-primary',
+          kind: 'agent',
+          label: 'Primary Agent',
+          position: { x: 200, y: 0 },
+          order: 0,
+          config: {
+            kind: 'agent',
+            id: 'agent-primary',
+            name: 'Primary Agent',
+            description: 'Handles the task.',
+            instructions: 'Do the work.',
+            model: 'gpt-5.4',
+            reasoningEffort: 'medium',
+          },
+        },
+        {
+          id: 'end',
+          kind: 'end',
+          label: 'End',
+          position: { x: 400, y: 0 },
+          config: { kind: 'end' },
+        },
+      ],
+      edges: [
+        { id: 'edge-start-agent', source: 'start', target: 'agent-primary', kind: 'direct' },
+        { id: 'edge-agent-end', source: 'agent-primary', target: 'end', kind: 'direct' },
+      ],
+    },
+    settings: {
+      checkpointing: { enabled: false },
+      executionMode: 'off-thread',
+    },
+  };
+}
+
+describe('workflow validation', () => {
+  test('accepts a simple start-agent-end workflow', () => {
+    expect(validateWorkflowDefinition(createWorkflow())).toEqual([]);
+  });
+
+  test('rejects unsupported node kinds in phase 1 backend', () => {
+    const workflow = createWorkflow();
+    workflow.graph.nodes.splice(1, 0, {
+      id: 'request-port',
+      kind: 'request-port',
+      label: 'Approval',
+      position: { x: 100, y: 0 },
+      config: {
+        kind: 'request-port',
+        portId: 'approval',
+        requestType: 'Question',
+        responseType: 'Answer',
+      },
+    });
+
+    expect(validateWorkflowDefinition(workflow).some((issue) =>
+      issue.message.includes('not executable yet'))).toBe(true);
+  });
+
+  test('builds a synthetic execution pattern from workflow agents', () => {
+    const pattern = buildWorkflowExecutionPattern(createWorkflow());
+
+    expect(pattern.id).toBe('workflow-1');
+    expect(pattern.agents).toHaveLength(1);
+    expect(pattern.agents[0]?.name).toBe('Primary Agent');
+    expect(pattern.graph?.nodes.map((node) => node.kind)).toEqual(['user-input', 'agent', 'user-output']);
+  });
+});