[$25 BOUNTY] [TypeScript] Add reconnect metrics for frontend sockets

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docs/OPERATIONS.md

@@ -310,3 +310,48 @@ Audit logs are retained for 365 days and include:
 2. Update Kubernetes secret: `kubectl create secret tls tot-tls --cert=new.crt --key=new.key -n tent-production --dry-run=client -o yaml | kubectl apply -f -`
 3. Restart services: `kubectl rollout restart deployment -n tent-production`
 4. Verify new certificate: `openssl s_client -connect api.example.com:443 -servername api.example.com`
+
+## Frontend WebSocket Reconnect Metrics
+
+The frontend exposes reconnect metrics for WebSocket connections through the
+`ReconnectMetrics` class in `frontend/src/services/reconnectMetrics.ts`.
+
+### Metrics Tracked
+
+| Metric | Type | Description |
+|--------|------|-------------|
+| `totalAttempts` | Counter | Total reconnect attempts since last reset |
+| `successfulReconnects` | Counter | Reconnects that re-established connection |
+| `failedReconnects` | Counter | Reconnect attempts that gave up after max retries |
+| `consecutiveFailures` | Gauge | Current consecutive failure count (resets on success) |
+| `lastBackoffMs` | Gauge | Last computed backoff delay in milliseconds |
+| `averageBackoffMs` | Gauge | Average backoff delay across all attempts |
+| `minBackoffMs` / `maxBackoffMs` | Gauge | Min/max observed backoff delays |
+| `lastAttemptAt` | Timestamp | Time of the last reconnect attempt |
+| `lastSuccessAt` | Timestamp | Time of the last successful reconnect |
+
+### Integration with useWebSocket Hook
+
+```typescript
+import { ReconnectMetrics } from '../services/reconnectMetrics';
+
+const reconnectMetrics = new ReconnectMetrics();
+
+// In the reconnect handler:
+reconnectMetrics.recordAttempt(computedDelay);
+
+// On successful reconnection:
+reconnectMetrics.recordSuccess(actualDelay);
+
+// On permanent failure:
+reconnectMetrics.recordFailure();
+
+// Get snapshot for telemetry:
+const snapshot = reconnectMetrics.snapshot();
+```
+
+### Running the Tests
+
+```bash
+cd frontend && npm test -- --run reconnectMetrics
+```

frontend/src/services/reconnectMetrics.test.ts

@@ -0,0 +1,93 @@
+import { describe, it, expect } from 'vitest';
+import { ReconnectMetrics } from '../services/reconnectMetrics';
+
+describe('ReconnectMetrics', () => {
+  it('starts with zero counts', () => {
+    const m = new ReconnectMetrics();
+    const snap = m.snapshot();
+    expect(snap.totalAttempts).toBe(0);
+    expect(snap.successfulReconnects).toBe(0);
+    expect(snap.failedReconnects).toBe(0);
+    expect(snap.consecutiveFailures).toBe(0);
+  });
+
+  it('records attempts', () => {
+    const m = new ReconnectMetrics();
+    m.recordAttempt(1000);
+    m.recordAttempt(2000);
+    expect(m.snapshot().totalAttempts).toBe(2);
+    expect(m.snapshot().lastBackoffMs).toBe(2000);
+  });
+
+  it('records successful reconnects', () => {
+    const m = new ReconnectMetrics();
+    m.recordAttempt(1000);
+    m.recordSuccess(1000);
+    expect(m.snapshot().successfulReconnects).toBe(1);
+    expect(m.snapshot().consecutiveFailures).toBe(0);
+    expect(m.snapshot().lastSuccessAt).not.toBeNull();
+  });
+
+  it('records failed reconnects and tracks consecutive failures', () => {
+    const m = new ReconnectMetrics();
+    m.recordFailure();
+    m.recordFailure();
+    expect(m.snapshot().failedReconnects).toBe(2);
+    expect(m.snapshot().consecutiveFailures).toBe(2);
+  });
+
+  it('resets consecutive failures on success', () => {
+    const m = new ReconnectMetrics();
+    m.recordFailure();
+    m.recordFailure();
+    expect(m.snapshot().consecutiveFailures).toBe(2);
+    m.recordSuccess(500);
+    expect(m.snapshot().consecutiveFailures).toBe(0);
+  });
+
+  it('tracks backoff statistics', () => {
+    const m = new ReconnectMetrics();
+    m.recordAttempt(1000);
+    m.recordAttempt(2000);
+    m.recordAttempt(4000);
+    const snap = m.snapshot();
+    expect(snap.minBackoffMs).toBe(1000);
+    expect(snap.maxBackoffMs).toBe(4000);
+    expect(snap.averageBackoffMs).toBe(2333); // (1000+2000+4000)/3 ≈ 2333
+  });
+
+  it('handles zero backoff (initial attempt)', () => {
+    const m = new ReconnectMetrics();
+    m.recordAttempt(0);
+    expect(m.snapshot().totalAttempts).toBe(1);
+    expect(m.snapshot().averageBackoffMs).toBe(0);
+    expect(m.snapshot().minBackoffMs).toBe(0);
+  });
+
+  it('resets all counters', () => {
+    const m = new ReconnectMetrics();
+    m.recordAttempt(1000);
+    m.recordSuccess(1000);
+    m.recordFailure();
+    m.reset();
+    const snap = m.snapshot();
+    expect(snap.totalAttempts).toBe(0);
+    expect(snap.successfulReconnects).toBe(0);
+    expect(snap.failedReconnects).toBe(0);
+    expect(snap.consecutiveFailures).toBe(0);
+    expect(snap.lastAttemptAt).toBeNull();
+    expect(snap.lastSuccessAt).toBeNull();
+    expect(snap.minBackoffMs).toBe(0);
+    expect(snap.maxBackoffMs).toBe(0);
+  });
+
+  it('snapshot returns lastAttemptAt timestamp', () => {
+    const m = new ReconnectMetrics();
+    const before = Date.now();
+    m.recordAttempt(500);
+    const after = Date.now();
+    const snap = m.snapshot();
+    expect(snap.lastAttemptAt).toBeGreaterThanOrEqual(before);
+    expect(snap.lastAttemptAt).toBeLessThanOrEqual(after);
+  });
+});

frontend/src/services/reconnectMetrics.ts

@@ -0,0 +1,117 @@
+/**
+ * WebSocket Reconnect Metrics
+ *
+ * Tracks reconnect attempts, successful reconnects, and backoff durations
+ * for frontend WebSocket connections. Designed to be reported to the
+ * telemetry service for monitoring and alerting.
+ *
+ * Usage:
+ *   const metrics = new ReconnectMetrics();
+ *   metrics.recordAttempt();
+ *   metrics.recordSuccess(45);  // reconnect took 45ms
+ *   metrics.recordFailure();
+ *   console.log(metrics.snapshot());
+ */
+
+export interface ReconnectMetricsSnapshot {
+  /** Total reconnect attempts since last reset */
+  totalAttempts: number;
+  /** Successful reconnects (connection re-established) */
+  successfulReconnects: number;
+  /** Failed reconnect attempts (gave up after max retries) */
+  failedReconnects: number;
+  /** Current consecutive failure count (resets on success) */
+  consecutiveFailures: number;
+  /** Last backoff delay in milliseconds */
+  lastBackoffMs: number;
+  /** Average backoff delay in milliseconds */
+  averageBackoffMs: number;
+  /** Minimum backoff delay observed */
+  minBackoffMs: number;
+  /** Maximum backoff delay observed */
+  maxBackoffMs: number;
+  /** Timestamp of the last reconnect attempt (ms since epoch) */
+  lastAttemptAt: number | null;
+  /** Timestamp of the last successful reconnect (ms since epoch) */
+  lastSuccessAt: number | null;
+}
+
+export class ReconnectMetrics {
+  private totalAttempts = 0;
+  private successfulReconnects = 0;
+  private failedReconnects = 0;
+  private consecutiveFailures = 0;
+  private backoffSum = 0;
+  private backoffCount = 0;
+  private _minBackoff = Infinity;
+  private _maxBackoff = 0;
+  private lastBackoffMs = 0;
+  private lastAttemptAt: number | null = null;
+  private lastSuccessAt: number | null = null;
+
+  /** Record a reconnect attempt with the computed backoff delay. */
+  recordAttempt(backoffMs: number = 0): void {
+    this.totalAttempts++;
+    this.lastAttemptAt = Date.now();
+    this.lastBackoffMs = backoffMs;
+
+    if (backoffMs > 0) {
+      this.backoffSum += backoffMs;
+      this.backoffCount++;
+      if (backoffMs < this._minBackoff) this._minBackoff = backoffMs;
+      if (backoffMs > this._maxBackoff) this._maxBackoff = backoffMs;
+    }
+  }
+
+  /** Record a successful reconnect (connection re-established). */
+  recordSuccess(backoffMs: number = 0): void {
+    this.successfulReconnects++;
+    this.consecutiveFailures = 0;
+    this.lastSuccessAt = Date.now();
+    this.lastBackoffMs = backoffMs;
+
+    if (backoffMs > 0) {
+      this.backoffSum += backoffMs;
+      this.backoffCount++;
+      if (backoffMs < this._minBackoff) this._minBackoff = backoffMs;
+      if (backoffMs > this._maxBackoff) this._maxBackoff = backoffMs;
+    }
+  }
+
+  /** Record a failed reconnect (gave up after max retries). */
+  recordFailure(): void {
+    this.failedReconnects++;
+    this.consecutiveFailures++;
+  }
+
+  /** Return a snapshot of the current metrics. */
+  snapshot(): ReconnectMetricsSnapshot {
+    return {
+      totalAttempts: this.totalAttempts,
+      successfulReconnects: this.successfulReconnects,
+      failedReconnects: this.failedReconnects,
+      consecutiveFailures: this.consecutiveFailures,
+      lastBackoffMs: this.lastBackoffMs,
+      averageBackoffMs: this.backoffCount > 0 ? Math.round(this.backoffSum / this.backoffCount) : 0,
+      minBackoffMs: this.backoffCount > 0 ? this._minBackoff : 0,
+      maxBackoffMs: this._maxBackoff,
+      lastAttemptAt: this.lastAttemptAt,
+      lastSuccessAt: this.lastSuccessAt,
+    };
+  }
+
+  /** Reset all counters. */
+  reset(): void {
+    this.totalAttempts = 0;
+    this.successfulReconnects = 0;
+    this.failedReconnects = 0;
+    this.consecutiveFailures = 0;
+    this.backoffSum = 0;
+    this.backoffCount = 0;
+    this._minBackoff = Infinity;
+    this._maxBackoff = 0;
+    this.lastBackoffMs = 0;
+    this.lastAttemptAt = null;
+    this.lastSuccessAt = null;
+  }
+}