refactor: remove legacy patterns system, unify on workflows

Remove the entire patterns domain model, IPC channels, sidecar services,
renderer components, and tests. Sessions now bind exclusively to workflows
via workflowId. Builtin workflows replace builtin patterns.

Backend:
- Make AgentNodeConfig standalone (no longer extends PatternAgentDefinition)
- Add WorkflowOrchestrationMode and WorkflowExecutionDefinition
- Create builtin workflows (single-agent, sequential, concurrent, handoff, group-chat)
- Rewrite session model config helpers for workflow-only
- Remove pattern IPC channels, handlers, and preload bindings
- Merge createSession/createWorkflowSession into single method
- Remove sidecar PatternGraphResolver, PatternValidator, pattern DTOs
- Add workspace migration for legacy sessions (patternId -> workflowId)

Frontend:
- Delete PatternEditor, pattern-graph components, patternGraph lib
- Delete NewSessionModal (session creation uses workflows directly)
- Remove PatternsSection from SettingsPanel
- Update App.tsx, ChatPane, ActivityPanel, Sidebar, RunTimeline,
  AgentConfigFields, InlinePills, sessionActivity to use workflow types
- Delete pattern.ts domain module

78 files changed across backend and frontend.

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

tests/shared/sessionLibrary.test.ts

@@ -9,30 +9,49 @@ import {
   renameSessionRecord,
   setSessionMessagePinnedRecord,
 } from '@shared/domain/sessionLibrary';
-import type { PatternDefinition } from '@shared/domain/pattern';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import type { ProjectRecord } from '@shared/domain/project';
 import type { SessionRecord } from '@shared/domain/session';
 import { createWorkspaceSettings } from '@shared/domain/tooling';
 import type { WorkspaceState } from '@shared/domain/workspace';
 
-function createPattern(overrides?: Partial<PatternDefinition>): PatternDefinition {
+function createWorkflow(overrides?: Partial<WorkflowDefinition>): WorkflowDefinition {
   return {
-    id: 'pattern-sequential-review',
+    id: 'workflow-sequential-review',
     name: 'Sequential Review',
     description: 'Multi-agent review workflow.',
-    mode: 'sequential',
-    availability: 'available',
-    maxIterations: 1,
-    agents: [
-      {
-        id: 'agent-analyst',
-        name: 'Analyst',
-        description: 'Reviews the request and finds issues.',
-        instructions: 'Analyze the request.',
-        model: 'gpt-5.4',
-        reasoningEffort: 'high',
-      },
-    ],
+    graph: {
+      nodes: [
+        { id: 'start', kind: 'start', label: 'Start', position: { x: 0, y: 0 }, config: { kind: 'start' } },
+        {
+          id: 'agent-analyst-node',
+          kind: 'agent',
+          label: 'Analyst',
+          position: { x: 200, y: 0 },
+          order: 0,
+          config: {
+            kind: 'agent',
+            id: 'agent-analyst',
+            name: 'Analyst',
+            description: 'Reviews the request and finds issues.',
+            instructions: 'Analyze the request.',
+            model: 'gpt-5.4',
+            reasoningEffort: 'high',
+          },
+        },
+        { id: 'end', kind: 'end', label: 'End', position: { x: 400, y: 0 }, config: { kind: 'end' } },
+      ],
+      edges: [
+        { id: 'edge-start-agent', source: 'start', target: 'agent-analyst-node', kind: 'direct' },
+        { id: 'edge-agent-end', source: 'agent-analyst-node', target: 'end', kind: 'direct' },
+      ],
+    },
+    settings: {
+      checkpointing: { enabled: false },
+      executionMode: 'off-thread',
+      orchestrationMode: 'sequential',
+      maxIterations: 1,
+    },
     createdAt: '2026-03-23T00:00:00.000Z',
     updatedAt: '2026-03-23T00:00:00.000Z',
     ...overrides,
@@ -53,7 +72,7 @@ function createSession(overrides?: Partial<SessionRecord>): SessionRecord {
   return {
     id: 'session-1',
     projectId: 'project-alpha',
-    patternId: 'pattern-sequential-review',
+    workflowId: 'workflow-sequential-review',
     title: 'Investigate Copilot refresh bug',
     createdAt: '2026-03-23T00:00:00.000Z',
     updatedAt: '2026-03-23T00:05:00.000Z',
@@ -75,8 +94,7 @@ function createSession(overrides?: Partial<SessionRecord>): SessionRecord {
 function createWorkspace(overrides?: Partial<WorkspaceState>): WorkspaceState {
   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: [],
+    workflows: [createWorkflow(), createWorkflow({ id: 'workflow-single-chat', name: '1-on-1 Copilot Chat', settings: { checkpointing: { enabled: false }, executionMode: 'off-thread', orchestrationMode: 'single', maxIterations: 1 } })],
     workflowTemplates: [],
     settings: createWorkspaceSettings(),
     sessions: [
@@ -84,7 +102,7 @@ function createWorkspace(overrides?: Partial<WorkspaceState>): WorkspaceState {
       createSession({
         id: 'session-2',
         projectId: 'project-scratchpad',
-        patternId: 'pattern-single-chat',
+        workflowId: 'workflow-single-chat',
         title: 'Scratchpad brainstorm',
         status: 'running',
         updatedAt: '2026-03-23T00:10:00.000Z',
@@ -109,7 +127,7 @@ function createWorkspace(overrides?: Partial<WorkspaceState>): WorkspaceState {
       }),
     ],
     selectedProjectId: 'project-alpha',
-    selectedPatternId: 'pattern-sequential-review',
+    selectedWorkflowId: 'workflow-sequential-review',
     selectedSessionId: 'session-1',
     lastUpdatedAt: '2026-03-23T00:10:00.000Z',
     ...overrides,
@@ -291,7 +309,7 @@ describe('session library helpers', () => {
 
     const branch = branchSessionRecord(
       sourceSession,
-      createPattern(),
+      createWorkflow(),
       'session-branch',
       'msg-3',
       '2026-03-23T00:04:00.000Z',
@@ -341,7 +359,7 @@ describe('session library helpers', () => {
     expect(() =>
       branchSessionRecord(
         sourceSession,
-        createPattern(),
+        createWorkflow(),
         'session-branch',
         'msg-1',
         '2026-03-23T00:04:00.000Z',
@@ -384,7 +402,7 @@ describe('session library helpers', () => {
 
     const branch = branchSessionRecord(
       sourceSession,
-      createPattern(),
+      createWorkflow(),
       'session-branch',
       'msg-2',
       '2026-03-23T00:05:00.000Z',
@@ -436,7 +454,7 @@ describe('session library helpers', () => {
 
     const regenerated = regenerateSessionRecord(
       sourceSession,
-      createPattern(),
+      createWorkflow(),
       'session-regenerated',
       'msg-4',
       '2026-03-23T00:06:00.000Z',
@@ -483,7 +501,7 @@ describe('session library helpers', () => {
     expect(() =>
       regenerateSessionRecord(
         sourceSession,
-        createPattern(),
+        createWorkflow(),
         'session-regenerated',
         'msg-2',
         '2026-03-23T00:06:00.000Z',
@@ -541,7 +559,7 @@ describe('session library helpers', () => {
 
     const edited = editAndResendSessionRecord(
       sourceSession,
-      createPattern(),
+      createWorkflow(),
       'session-edited',
       'msg-3',
       'Focus on session state only.',
@@ -585,7 +603,7 @@ describe('session library helpers', () => {
       {
         sessionId: 'session-1',
         score: 31,
-        matchedFields: ['title', 'message', 'project', 'pattern'],
+        matchedFields: ['title', 'message', 'project', 'workflow'],
       },
     ]);
   });