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/session.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, test } from 'bun:test';
 
-import type { PatternDefinition } from '@shared/domain/pattern';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import {
   applySessionApprovalSettings,
   applySessionModelConfig,
@@ -12,42 +12,70 @@ import {
   type SessionRecord,
 } from '@shared/domain/session';
 
-function createPattern(): PatternDefinition {
+function createWorkflow(): WorkflowDefinition {
   return {
-    id: 'pattern-single',
+    id: 'workflow-single',
     name: '1-on-1 Copilot Chat',
     description: 'Single agent chat',
-    mode: 'single',
-    availability: 'available',
-    maxIterations: 1,
-    agents: [
-      {
-        id: 'agent-primary',
-        name: 'Primary Agent',
-        description: 'Helpful assistant',
-        instructions: 'Help the user.',
-        model: 'gpt-5.4',
-        reasoningEffort: 'high',
-      },
-      {
-        id: 'agent-secondary',
-        name: 'Secondary Agent',
-        description: 'Unused here',
-        instructions: 'Review.',
-        model: 'claude-sonnet-4.5',
-        reasoningEffort: 'medium',
-      },
-    ],
+    graph: {
+      nodes: [
+        { id: 'start', kind: 'start', label: 'Start', position: { x: 0, y: 0 }, config: { kind: 'start' } },
+        {
+          id: 'agent-primary-node',
+          kind: 'agent',
+          label: 'Primary Agent',
+          position: { x: 200, y: 0 },
+          order: 0,
+          config: {
+            kind: 'agent',
+            id: 'agent-primary',
+            name: 'Primary Agent',
+            description: 'Helpful assistant',
+            instructions: 'Help the user.',
+            model: 'gpt-5.4',
+            reasoningEffort: 'high',
+          },
+        },
+        {
+          id: 'agent-secondary-node',
+          kind: 'agent',
+          label: 'Secondary Agent',
+          position: { x: 400, y: 0 },
+          order: 1,
+          config: {
+            kind: 'agent',
+            id: 'agent-secondary',
+            name: 'Secondary Agent',
+            description: 'Unused here',
+            instructions: 'Review.',
+            model: 'claude-sonnet-4.5',
+            reasoningEffort: 'medium',
+          },
+        },
+        { id: 'end', kind: 'end', label: 'End', position: { x: 600, y: 0 }, config: { kind: 'end' } },
+      ],
+      edges: [
+        { id: 'edge-start-primary', source: 'start', target: 'agent-primary-node', kind: 'direct' },
+        { id: 'edge-primary-secondary', source: 'agent-primary-node', target: 'agent-secondary-node', kind: 'direct' },
+        { id: 'edge-secondary-end', source: 'agent-secondary-node', target: 'end', kind: 'direct' },
+      ],
+    },
+    settings: {
+      checkpointing: { enabled: false },
+      executionMode: 'off-thread',
+      orchestrationMode: 'single',
+      maxIterations: 1,
+    },
     createdAt: '2026-03-23T00:00:00.000Z',
     updatedAt: '2026-03-23T00:00:00.000Z',
   };
 }
 
 function createSession(overrides?: Partial<SessionRecord>): SessionRecord {
-  return {
-    id: 'session-1',
-    projectId: 'project-scratchpad',
-    patternId: 'pattern-single',
+    return {
+      id: 'session-1',
+      projectId: 'project-scratchpad',
+      workflowId: 'workflow-single',
     title: 'Scratchpad',
     createdAt: '2026-03-23T00:00:00.000Z',
     updatedAt: '2026-03-23T00:00:00.000Z',
@@ -60,13 +88,13 @@ function createSession(overrides?: Partial<SessionRecord>): SessionRecord {
 
 describe('session model config helpers', () => {
   test('captures the initial model settings from the primary agent', () => {
-    expect(createSessionModelConfig(createPattern())).toEqual({
+    expect(createSessionModelConfig(createWorkflow())).toEqual({
       model: 'gpt-5.4',
       reasoningEffort: 'high',
     });
   });
 
-  test('resolves persisted session overrides over the pattern defaults', () => {
+  test('resolves persisted session overrides over the workflow defaults', () => {
     const config = resolveSessionModelConfig(
       createSession({
         sessionModelConfig: {
@@ -74,7 +102,7 @@ describe('session model config helpers', () => {
           reasoningEffort: 'medium',
         },
       }),
-      createPattern(),
+      createWorkflow(),
     );
 
     expect(config).toEqual({
@@ -84,9 +112,9 @@ describe('session model config helpers', () => {
   });
 
   test('applies session model settings only to the primary agent', () => {
-    const pattern = createPattern();
+    const workflow = createWorkflow();
     const updated = applySessionModelConfig(
-      pattern,
+      workflow,
       createSession({
         sessionModelConfig: {
           model: 'gpt-5.4-mini',
@@ -95,22 +123,25 @@ describe('session model config helpers', () => {
       }),
     );
 
-    expect(updated.agents[0].model).toBe('gpt-5.4-mini');
-    expect(updated.agents[0].reasoningEffort).toBe('low');
-    expect(updated.agents[1]).toEqual(pattern.agents[1]);
+    const primaryAgent = updated.graph.nodes[1];
+    const secondaryAgent = updated.graph.nodes[2];
+    const originalSecondaryAgent = workflow.graph.nodes[2];
+    expect(primaryAgent?.config.kind === 'agent' ? primaryAgent.config.model : undefined).toBe('gpt-5.4-mini');
+    expect(primaryAgent?.config.kind === 'agent' ? primaryAgent.config.reasoningEffort : undefined).toBe('low');
+    expect(secondaryAgent).toEqual(originalSecondaryAgent);
   });
 });
 
 describe('session title helpers', () => {
   test('keeps a manual title instead of recomputing it from the first user message', () => {
-    const pattern = createPattern();
+    const workflow = createWorkflow();
     const session = createSession({
       title: 'Release readiness review',
       titleSource: 'manual',
     });
 
     expect(
-      resolveSessionTitle(session, pattern, [
+      resolveSessionTitle(session, workflow, [
         {
           id: 'msg-1',
           role: 'user',
@@ -123,11 +154,11 @@ describe('session title helpers', () => {
   });
 
   test('builds auto titles from markdown-heavy first messages', () => {
-    const pattern = createPattern();
+    const workflow = createWorkflow();
     const session = createSession();
 
     expect(
-      resolveSessionTitle(session, pattern, [
+      resolveSessionTitle(session, workflow, [
         {
           id: 'msg-1',
           role: 'user',
@@ -164,25 +195,28 @@ describe('session tooling helpers', () => {
 });
 
 describe('session approval helpers', () => {
-  test('normalizes session approval overrides and applies them over pattern defaults', () => {
-    const pattern = {
-      ...createPattern(),
-      approvalPolicy: {
-        rules: [{ kind: 'tool-call' as const }],
-        autoApprovedToolNames: ['git.status'],
+  test('normalizes session approval overrides and applies them over workflow defaults', () => {
+    const workflow = {
+      ...createWorkflow(),
+      settings: {
+        ...createWorkflow().settings,
+        approvalPolicy: {
+          rules: [{ kind: 'tool-call' as const }],
+          autoApprovedToolNames: ['git.status'],
+        },
       },
     };
 
     expect(resolveSessionApprovalSettings(createSession())).toBeUndefined();
     expect(
-      applySessionApprovalSettings(
-        pattern,
-        createSession({
+        applySessionApprovalSettings(
+          workflow,
+          createSession({
           approvalSettings: {
             autoApprovedToolNames: ['git.diff', ' git.diff '],
           },
         }),
-      ).approvalPolicy,
+        ).settings.approvalPolicy,
     ).toEqual({
       rules: [{ kind: 'tool-call' }],
       autoApprovedToolNames: ['git.diff'],