fix: refactor telemetry system with critical improvements (v2.14.1)

Major improvements to telemetry system addressing code review findings:

Architecture & Modularization:
- Split 636-line TelemetryManager into 7 focused modules
- Separated concerns: event tracking, batch processing, validation, rate limiting
- Lazy initialization pattern to avoid early singleton creation
- Clean separation of responsibilities

Security & Privacy:
- Added comprehensive input validation with Zod schemas
- Sanitization of sensitive data (URLs, API keys, emails)
- Expanded sensitive key detection patterns (25+ patterns)
- Row Level Security on Supabase backend
- Added data deletion contact info (romuald@n8n-mcp.com)

Performance & Reliability:
- Sliding window rate limiter (100 events/minute)
- Circuit breaker pattern for network failures
- Dead letter queue for failed events
- Exponential backoff with jitter for retries
- Performance monitoring with overhead tracking (<5%)
- Memory-safe array limits in rate limiter

Testing:
- Comprehensive test coverage (87%+ for core modules)
- Unit tests for all new modules
- Integration tests for MCP telemetry
- Fixed test isolation issues

Data Management:
- Clear user consent in welcome message
- Batch processing with deduplication
- Automatic workflow flushing

BREAKING CHANGE: TelemetryManager constructor is now private, use getInstance()

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/telemetry/rate-limiter.ts

@@ -0,0 +1,173 @@
+/**
+ * Rate Limiter for Telemetry
+ * Implements sliding window rate limiting to prevent excessive telemetry events
+ */
+
+import { TELEMETRY_CONFIG } from './telemetry-types';
+import { logger } from '../utils/logger';
+
+export class TelemetryRateLimiter {
+  private eventTimestamps: number[] = [];
+  private windowMs: number;
+  private maxEvents: number;
+  private droppedEventsCount: number = 0;
+  private lastWarningTime: number = 0;
+  private readonly WARNING_INTERVAL = 60000; // Warn at most once per minute
+  private readonly MAX_ARRAY_SIZE = 1000; // Prevent memory leaks by limiting array size
+
+  constructor(
+    windowMs: number = TELEMETRY_CONFIG.RATE_LIMIT_WINDOW,
+    maxEvents: number = TELEMETRY_CONFIG.RATE_LIMIT_MAX_EVENTS
+  ) {
+    this.windowMs = windowMs;
+    this.maxEvents = maxEvents;
+  }
+
+  /**
+   * Check if an event can be tracked based on rate limits
+   * Returns true if event can proceed, false if rate limited
+   */
+  allow(): boolean {
+    const now = Date.now();
+
+    // Clean up old timestamps outside the window
+    this.cleanupOldTimestamps(now);
+
+    // Check if we've hit the rate limit
+    if (this.eventTimestamps.length >= this.maxEvents) {
+      this.handleRateLimitHit(now);
+      return false;
+    }
+
+    // Add current timestamp and allow event
+    this.eventTimestamps.push(now);
+    return true;
+  }
+
+  /**
+   * Check if rate limiting would occur without actually blocking
+   * Useful for pre-flight checks
+   */
+  wouldAllow(): boolean {
+    const now = Date.now();
+    this.cleanupOldTimestamps(now);
+    return this.eventTimestamps.length < this.maxEvents;
+  }
+
+  /**
+   * Get current usage statistics
+   */
+  getStats() {
+    const now = Date.now();
+    this.cleanupOldTimestamps(now);
+
+    return {
+      currentEvents: this.eventTimestamps.length,
+      maxEvents: this.maxEvents,
+      windowMs: this.windowMs,
+      droppedEvents: this.droppedEventsCount,
+      utilizationPercent: Math.round((this.eventTimestamps.length / this.maxEvents) * 100),
+      remainingCapacity: Math.max(0, this.maxEvents - this.eventTimestamps.length),
+      arraySize: this.eventTimestamps.length,
+      maxArraySize: this.MAX_ARRAY_SIZE,
+      memoryUsagePercent: Math.round((this.eventTimestamps.length / this.MAX_ARRAY_SIZE) * 100)
+    };
+  }
+
+  /**
+   * Reset the rate limiter (useful for testing)
+   */
+  reset(): void {
+    this.eventTimestamps = [];
+    this.droppedEventsCount = 0;
+    this.lastWarningTime = 0;
+  }
+
+  /**
+   * Clean up timestamps outside the current window and enforce array size limit
+   */
+  private cleanupOldTimestamps(now: number): void {
+    const windowStart = now - this.windowMs;
+
+    // Remove all timestamps before the window start
+    let i = 0;
+    while (i < this.eventTimestamps.length && this.eventTimestamps[i] < windowStart) {
+      i++;
+    }
+
+    if (i > 0) {
+      this.eventTimestamps.splice(0, i);
+    }
+
+    // Enforce maximum array size to prevent memory leaks
+    if (this.eventTimestamps.length > this.MAX_ARRAY_SIZE) {
+      const excess = this.eventTimestamps.length - this.MAX_ARRAY_SIZE;
+      this.eventTimestamps.splice(0, excess);
+
+      if (now - this.lastWarningTime > this.WARNING_INTERVAL) {
+        logger.debug(
+          `Telemetry rate limiter array trimmed: removed ${excess} oldest timestamps to prevent memory leak. ` +
+          `Array size: ${this.eventTimestamps.length}/${this.MAX_ARRAY_SIZE}`
+        );
+        this.lastWarningTime = now;
+      }
+    }
+  }
+
+  /**
+   * Handle rate limit hit
+   */
+  private handleRateLimitHit(now: number): void {
+    this.droppedEventsCount++;
+
+    // Log warning if enough time has passed since last warning
+    if (now - this.lastWarningTime > this.WARNING_INTERVAL) {
+      const stats = this.getStats();
+      logger.debug(
+        `Telemetry rate limit reached: ${stats.currentEvents}/${stats.maxEvents} events in ${stats.windowMs}ms window. ` +
+        `Total dropped: ${stats.droppedEvents}`
+      );
+      this.lastWarningTime = now;
+    }
+  }
+
+  /**
+   * Get the number of dropped events
+   */
+  getDroppedEventsCount(): number {
+    return this.droppedEventsCount;
+  }
+
+  /**
+   * Estimate time until capacity is available (in ms)
+   * Returns 0 if capacity is available now
+   */
+  getTimeUntilCapacity(): number {
+    const now = Date.now();
+    this.cleanupOldTimestamps(now);
+
+    if (this.eventTimestamps.length < this.maxEvents) {
+      return 0;
+    }
+
+    // Find the oldest timestamp that would need to expire
+    const oldestRelevant = this.eventTimestamps[this.eventTimestamps.length - this.maxEvents];
+    const timeUntilExpiry = Math.max(0, (oldestRelevant + this.windowMs) - now);
+
+    return timeUntilExpiry;
+  }
+
+  /**
+   * Update rate limit configuration dynamically
+   */
+  updateLimits(windowMs?: number, maxEvents?: number): void {
+    if (windowMs !== undefined && windowMs > 0) {
+      this.windowMs = windowMs;
+    }
+    if (maxEvents !== undefined && maxEvents > 0) {
+      this.maxEvents = maxEvents;
+    }
+
+    logger.debug(`Rate limiter updated: ${this.maxEvents} events per ${this.windowMs}ms`);
+  }
+}