feat(observability): P3.2-A/B/C Enhanced observability coverage

P3.2-A: Expanded event coverage
- Added recovery events (RECOVERY_START, RECOVERY_COMPLETE, RECOVERY_ERROR)
- Added database events (DB_QUERY_START, DB_QUERY_COMPLETE, DB_QUERY_ERROR)
- Added state transition event (STATE_TRANSITION)
- Added background task events (BACKGROUND_TASK_START, COMPLETE, ERROR)

P3.2-B: Structured metrics export
- Added exportMetrics() method to export all metrics as JSON
- Added getMetricsSummary() method for lightweight metrics summary

P3.2-C: Improved error context
- Added toJSON() method to DailyNotificationError for structured logging
- Added logError() method to ObservabilityManager with enhanced error context

Verification:
- TypeScript compiles ✅
- No new dependencies ✅
- JSON export is valid ✅

src/core/errors.ts

@@ -106,6 +106,20 @@ export class DailyNotificationError extends Error {
     };
   }
   
+  /**
+   * Convert error to JSON for structured logging
+   * @returns JSON-serializable error representation
+   */
+  toJSON(): Record<string, unknown> {
+    return {
+      code: this.code,
+      message: this.message,
+      stack: this.stack,
+      timestamp: Date.now(),
+      ...(this.details && { details: this.details }),
+    };
+  }
+  
   /**
    * Create error for missing required parameter
    */

src/core/events.ts

@@ -76,6 +76,20 @@ export const EVENT_CODES = {
   ANDROID_WORKMANAGER_START: 'DNP-ANDROID-WM-START',
   IOS_BGTASK_START: 'DNP-IOS-BGTASK-START',
   ELECTRON_NOTIFICATION: 'DNP-ELECTRON-NOTIFICATION',
+  // Recovery events
+  RECOVERY_START: 'DNP-RECOVERY-START',
+  RECOVERY_COMPLETE: 'DNP-RECOVERY-COMPLETE',
+  RECOVERY_ERROR: 'DNP-RECOVERY-ERROR',
+  // Database events
+  DB_QUERY_START: 'DNP-DB-QUERY-START',
+  DB_QUERY_COMPLETE: 'DNP-DB-QUERY-COMPLETE',
+  DB_QUERY_ERROR: 'DNP-DB-QUERY-ERROR',
+  // State transition events
+  STATE_TRANSITION: 'DNP-STATE-TRANSITION',
+  // Background task events
+  BACKGROUND_TASK_START: 'DNP-BG-TASK-START',
+  BACKGROUND_TASK_COMPLETE: 'DNP-BG-TASK-COMPLETE',
+  BACKGROUND_TASK_ERROR: 'DNP-BG-TASK-ERROR',
 } as const;
 
 /**

src/observability.ts

@@ -11,6 +11,7 @@ import {
   EVENT_CODES,
   createEventLog,
 } from './core/events';
+import { DailyNotificationError } from './core/errors';
 
 export interface HealthStatus {
   nextRuns: number[];
@@ -134,6 +135,32 @@ export class ObservabilityManager {
     }
   }
 
+  /**
+   * Log error with enhanced context
+   * @param eventCode Event code
+   * @param message Human-readable message
+   * @param error Error object
+   * @param context Additional context
+   */
+  logError(eventCode: string, message: string, error: Error, context?: Record<string, unknown>): void {
+    const errorData: Record<string, unknown> = {
+      error: error.message,
+      errorCode: error instanceof DailyNotificationError ? error.code : undefined,
+      errorName: error.name,
+      ...(error instanceof DailyNotificationError && error.details ? { errorDetails: error.details } : {}),
+      ...(error.stack ? { stack: error.stack } : {}),
+      ...context,
+    };
+
+    // Use toJSON if available for structured error data
+    if (error instanceof DailyNotificationError && typeof (error as unknown as { toJSON?: () => Record<string, unknown> }).toJSON === 'function') {
+      const jsonError = (error as unknown as { toJSON: () => Record<string, unknown> }).toJSON();
+      Object.assign(errorData, jsonError);
+    }
+
+    this.logEvent('ERROR', eventCode, message, errorData);
+  }
+
   /**
    * Record performance metrics
    */
@@ -204,6 +231,47 @@ export class ObservabilityManager {
     };
   }
 
+  /**
+   * Export metrics as JSON
+   * @returns JSON string of all metrics
+   */
+  exportMetrics(): string {
+    return JSON.stringify({
+      performance: this.performanceMetrics,
+      user: this.userMetrics,
+      platform: this.platformMetrics,
+      events: this.eventLogs.slice(0, 100), // Last 100 events
+      exportedAt: Date.now(),
+      schemaVersion: 1
+    }, null, 2);
+  }
+
+  /**
+   * Get metrics summary (lightweight)
+   * @returns Summary object
+   */
+  getMetricsSummary(): {
+    eventCount: number;
+    successRate: number;
+    avgFetchTime: number;
+    avgNotifyTime: number;
+  } {
+    const fetchTimes = this.performanceMetrics.fetchTimes;
+    const notifyTimes = this.performanceMetrics.notifyTimes;
+    const total = this.performanceMetrics.successCount + this.performanceMetrics.failureCount;
+    
+    return {
+      eventCount: this.eventLogs.length,
+      successRate: total > 0 ? this.performanceMetrics.successCount / total : 0,
+      avgFetchTime: fetchTimes.length > 0 
+        ? fetchTimes.reduce((a, b) => a + b, 0) / fetchTimes.length 
+        : 0,
+      avgNotifyTime: notifyTimes.length > 0
+        ? notifyTimes.reduce((a, b) => a + b, 0) / notifyTimes.length
+        : 0
+    };
+  }
+
   /**
    * Get recent event logs
    */