Diagnostics: bound in-memory session state tracking

src/logging/diagnostic.test.ts

@@ -0,0 +1,36 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  getDiagnosticSessionStateCountForTest,
+  logSessionStateChange,
+  resetDiagnosticStateForTest,
+} from "./diagnostic.js";
+
+describe("diagnostic session state pruning", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+    resetDiagnosticStateForTest();
+  });
+
+  afterEach(() => {
+    resetDiagnosticStateForTest();
+    vi.useRealTimers();
+  });
+
+  it("evicts stale idle session states", () => {
+    logSessionStateChange({ sessionId: "stale-1", state: "idle" });
+    expect(getDiagnosticSessionStateCountForTest()).toBe(1);
+
+    vi.advanceTimersByTime(31 * 60 * 1000);
+    logSessionStateChange({ sessionId: "fresh-1", state: "idle" });
+
+    expect(getDiagnosticSessionStateCountForTest()).toBe(1);
+  });
+
+  it("caps tracked session states to a bounded max", () => {
+    for (let i = 0; i < 2105; i += 1) {
+      logSessionStateChange({ sessionId: `session-${i}`, state: "idle" });
+    }
+
+    expect(getDiagnosticSessionStateCountForTest()).toBe(2000);
+  });
+});