[claude] API observability — structured logging + /api/metrics endpoint (#57) (#87)

artifacts/api-server/src/lib/request-counters.ts

@@ -0,0 +1,37 @@
+/** In-memory HTTP request counters for the /api/metrics endpoint. */
+
+export interface RequestCountsSnapshot {
+  total: number;
+  by_status: Record<string, number>;
+  errors_4xx: number;
+  errors_5xx: number;
+}
+
+class RequestCounters {
+  private total = 0;
+  private byStatus: Record<number, number> = {};
+  private errors4xx = 0;
+  private errors5xx = 0;
+
+  record(statusCode: number): void {
+    this.total++;
+    this.byStatus[statusCode] = (this.byStatus[statusCode] ?? 0) + 1;
+    if (statusCode >= 400 && statusCode < 500) this.errors4xx++;
+    else if (statusCode >= 500) this.errors5xx++;
+  }
+
+  snapshot(): RequestCountsSnapshot {
+    const byStatus: Record<string, number> = {};
+    for (const [code, count] of Object.entries(this.byStatus)) {
+      byStatus[code] = count;
+    }
+    return {
+      total: this.total,
+      by_status: byStatus,
+      errors_4xx: this.errors4xx,
+      errors_5xx: this.errors5xx,
+    };
+  }
+}
+
+export const requestCounters = new RequestCounters();