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>

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']);
+  });
+});