feat(service): add Service and ServiceManager for component lifecycle management

Adds two new classes:
- Service: long-running component with start/stop lifecycle, health checks, builder pattern and subclass support
- ServiceManager: orchestrates multiple services with dependency-ordered startup, failure isolation, retry with backoff, and reverse-order shutdown

ts/taskbuffer.interfaces.ts

@@ -79,4 +79,101 @@ export interface ITaskEvent {
   timestamp: number;
   stepName?: string;   // present when type === 'step'
   error?: string;      // present when type === 'failed'
+}
+
+// ── Service Lifecycle Types ──────────────────────────────────────
+
+export type TServiceState =
+  | 'stopped'
+  | 'starting'
+  | 'running'
+  | 'degraded'
+  | 'failed'
+  | 'stopping';
+
+export type TServiceCriticality = 'critical' | 'optional';
+
+export type TServiceEventType =
+  | 'started'
+  | 'stopped'
+  | 'failed'
+  | 'degraded'
+  | 'recovered'
+  | 'retrying'
+  | 'healthCheck';
+
+export interface IServiceEvent {
+  type: TServiceEventType;
+  serviceName: string;
+  state: TServiceState;
+  timestamp: number;
+  error?: string;
+  attempt?: number;
+}
+
+export interface IServiceStatus {
+  name: string;
+  state: TServiceState;
+  criticality: TServiceCriticality;
+  startedAt?: number;
+  stoppedAt?: number;
+  lastHealthCheck?: number;
+  healthCheckOk?: boolean;
+  uptime?: number;
+  errorCount: number;
+  lastError?: string;
+  retryCount: number;
+  dependencies: string[];
+}
+
+export interface IRetryConfig {
+  /** Maximum retry attempts. 0 = no retries. Default: 3 */
+  maxRetries?: number;
+  /** Base delay in ms. Default: 1000 */
+  baseDelayMs?: number;
+  /** Maximum delay cap in ms. Default: 30000 */
+  maxDelayMs?: number;
+  /** Multiplier per attempt. Default: 2 */
+  backoffFactor?: number;
+}
+
+export interface IHealthCheckConfig {
+  /** Interval in ms between health checks. Default: 30000 */
+  intervalMs?: number;
+  /** Timeout for a single health check call. Default: 5000 */
+  timeoutMs?: number;
+  /** Consecutive failures before marking degraded. Default: 3 */
+  failuresBeforeDegraded?: number;
+  /** Consecutive failures before marking failed. Default: 5 */
+  failuresBeforeFailed?: number;
+}
+
+export interface IServiceOptions<T = any> {
+  name: string;
+  start: () => Promise<T>;
+  stop: () => Promise<void>;
+  healthCheck?: () => Promise<boolean>;
+  criticality?: TServiceCriticality;
+  dependencies?: string[];
+  retry?: IRetryConfig;
+  healthCheckConfig?: IHealthCheckConfig;
+}
+
+export interface IServiceManagerOptions {
+  name?: string;
+  defaultRetry?: IRetryConfig;
+  defaultHealthCheck?: IHealthCheckConfig;
+  /** Timeout in ms for the entire startup sequence. Default: 120000 */
+  startupTimeoutMs?: number;
+  /** Timeout in ms for the entire shutdown sequence. Default: 30000 */
+  shutdownTimeoutMs?: number;
+}
+
+export type TOverallHealth = 'healthy' | 'degraded' | 'unhealthy';
+
+export interface IServiceManagerHealth {
+  overall: TOverallHealth;
+  services: IServiceStatus[];
+  startedAt?: number;
+  uptime?: number;
 }