feat: full Copilot SDK feature parity — custom agents, hooks, image input, skills, steering, session persistence

Backend (sidecar):
- Extended ProtocolModels with DTOs for custom agents, hooks, skills,
  infinite sessions, session lifecycle, and 9 new event types
- Added CopilotManagedSessionIds for stable SDK session ID mapping
- Added CopilotSessionManager/ICopilotSessionManager for session lifecycle
- Added CopilotSessionHooks for hook registration
- Added CopilotMessageOptionsMetadata for mid-turn steering
- Extended CopilotAgentBundle to wire custom agents, hooks, skills,
  infinite sessions, and stable session IDs
- Extended CopilotTurnExecutionState to project 13 new SDK event types
- Widened ITurnWorkflowRunner callback to accept SidecarEventDto
- Added list/delete/disconnect session commands to SidecarProtocolHost
- Added AryxCopilotAgentMessageOptionsTests (14 new tests, 142 total)

Frontend (renderer + main + shared):
- Added ChatMessageAttachment type and helpers (attachment.ts)
- Extended sidecar contracts with MessageMode, 3 new command types,
  9 new event types, and agent/session config DTOs
- Extended SessionEventRecord with 6 new event kinds and ~20 fields
- Added PatternAgentCopilotConfig to pattern domain
- Added attachments support to ChatMessageRecord
- Updated sidecar client with session lifecycle methods and
  turn-scoped event routing via onTurnScopedEvent callback
- Updated main process: handleTurnScopedEvent(), deleteSession(),
  steering bypass for mid-turn messages, attachment passthrough
- Added deleteSession IPC handler and preload binding
- Added TurnEventLog state tracker with format/apply/prune helpers
- ChatPane: always-enabled composer, steering indicator, attachment
  picker with preview, image thumbnails in message history,
  context-usage bar, amber steer mode for send button
- ActivityPanel: turn events section with sub-agent, hook, skill,
  and compaction event rendering
- Sidebar: delete session action in context menu
- App.tsx: wired sessionUsage, turnEventLogs, and deleteSession

Documentation:
- AGENTS.md: added glob safety rule for node_modules
- README.md: added steering, image input, and richer observability
- ARCHITECTURE.md: added turn-scoped events, steering, and attachments
- Website: added steering and image input feature cards, updated
  live visibility and session cards

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

src/shared/domain/attachment.ts

@@ -0,0 +1,42 @@
+export type ChatMessageAttachmentType = 'file' | 'blob';
+
+export interface ChatMessageAttachment {
+  type: ChatMessageAttachmentType;
+  path?: string;
+  data?: string;
+  mimeType?: string;
+  displayName?: string;
+}
+
+const supportedImageMimeTypes = new Set([
+  'image/jpeg',
+  'image/png',
+  'image/gif',
+  'image/webp',
+]);
+
+export function isImageAttachment(attachment: ChatMessageAttachment): boolean {
+  if (attachment.mimeType) {
+    return supportedImageMimeTypes.has(attachment.mimeType);
+  }
+
+  if (attachment.path) {
+    const ext = attachment.path.split('.').pop()?.toLowerCase();
+    return ext === 'jpg' || ext === 'jpeg' || ext === 'png' || ext === 'gif' || ext === 'webp';
+  }
+
+  return false;
+}
+
+export function getAttachmentDisplayName(attachment: ChatMessageAttachment): string {
+  if (attachment.displayName) {
+    return attachment.displayName;
+  }
+
+  if (attachment.path) {
+    const parts = attachment.path.replace(/\\/g, '/').split('/');
+    return parts[parts.length - 1] || attachment.path;
+  }
+
+  return attachment.mimeType ?? 'Attachment';
+}

src/shared/domain/event.ts

@@ -8,7 +8,15 @@ export type SessionEventKind =
   | 'message-complete'
   | 'agent-activity'
   | 'run-updated'
-  | 'error';
+  | 'error'
+  | 'subagent'
+  | 'skill-invoked'
+  | 'hook-lifecycle'
+  | 'session-usage'
+  | 'session-compaction'
+  | 'pending-messages-modified';
+
+export type SubagentEventKind = 'started' | 'completed' | 'failed' | 'selected' | 'deselected';
 
 export interface SessionEventRecord {
   sessionId: string;
@@ -27,4 +35,32 @@ export interface SessionEventRecord {
   toolName?: string;
   run?: SessionRunRecord;
   error?: string;
+
+  // Subagent event fields
+  subagentEventKind?: SubagentEventKind;
+  customAgentName?: string;
+  customAgentDisplayName?: string;
+
+  // Skill invoked fields
+  skillName?: string;
+  skillPath?: string;
+  pluginName?: string;
+
+  // Hook lifecycle fields
+  hookInvocationId?: string;
+  hookType?: string;
+  hookPhase?: 'start' | 'end';
+  hookSuccess?: boolean;
+
+  // Session usage fields
+  tokenLimit?: number;
+  currentTokens?: number;
+  messagesLength?: number;
+
+  // Session compaction fields
+  compactionPhase?: 'start' | 'complete';
+  compactionSuccess?: boolean;
+  preCompactionTokens?: number;
+  postCompactionTokens?: number;
+  tokensRemoved?: number;
 }

src/shared/domain/pattern.ts

@@ -32,6 +32,8 @@ export const reasoningEffortOptions: ReadonlyArray<{ value: ReasoningEffort; lab
   { value: 'xhigh', label: 'Maximum' },
 ];
 
+import type { PatternAgentCopilotConfig } from '@shared/contracts/sidecar';
+
 export interface PatternAgentDefinition {
   id: string;
   name: string;
@@ -39,6 +41,7 @@ export interface PatternAgentDefinition {
   instructions: string;
   model: string;
   reasoningEffort?: ReasoningEffort;
+  copilot?: PatternAgentCopilotConfig;
 }
 
 export interface PatternGraphPosition {

src/shared/domain/session.ts

@@ -14,6 +14,7 @@ import type { SessionRunRecord } from '@shared/domain/runTimeline';
 import type { PendingUserInputRecord } from '@shared/domain/userInput';
 import type { PendingPlanReviewRecord } from '@shared/domain/planReview';
 import type { PendingMcpAuthRecord } from '@shared/domain/mcpAuth';
+import type { ChatMessageAttachment } from '@shared/domain/attachment';
 import type { InteractionMode } from '@shared/contracts/sidecar';
 
 export type ChatRole = 'system' | 'user' | 'assistant';
@@ -32,6 +33,7 @@ export interface ChatMessageRecord {
   content: string;
   createdAt: string;
   pending?: boolean;
+  attachments?: ChatMessageAttachment[];
 }
 
 export interface SessionRecord {