diff --git a/tests/management-api-logs-metrics.test.ts b/tests/management-api-logs-metrics.test.ts
index b24b9e6d3..f7077a895 100644
--- a/tests/management-api-logs-metrics.test.ts
+++ b/tests/management-api-logs-metrics.test.ts
@@ -1,5 +1,9 @@
-import { afterEach, describe, expect, test } from "bun:test";
+import { afterEach, beforeEach, describe, expect, test } from "bun:test";
+import { existsSync, mkdtempSync, readFileSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { handleManagementAPI } from "../src/server/management-api";
+import { usageLogPath } from "../src/usage/log";
 import {
   addRequestLog,
   clearRequestLogsForTests,
@@ -10,7 +14,24 @@ import type { OcxConfig } from "../src/types";
 
 const config = { providers: [] } as unknown as OcxConfig;
 
-afterEach(() => clearRequestLogsForTests());
+let testDir = "";
+let previousHome: string | undefined;
+
+beforeEach(() => {
+  // addRequestLog persists to usage.jsonl; without a scratch OPENCODEX_HOME a bare
+  // `bun test <file>` run from outside the repo (no bunfig preload) writes these
+  // fixture rows into the real ~/.opencodex log and poisons the GUI Usage page.
+  previousHome = process.env.OPENCODEX_HOME;
+  testDir = mkdtempSync(join(tmpdir(), "ocx-logs-metrics-"));
+  process.env.OPENCODEX_HOME = testDir;
+});
+
+afterEach(() => {
+  clearRequestLogsForTests();
+  if (previousHome === undefined) delete process.env.OPENCODEX_HOME;
+  else process.env.OPENCODEX_HOME = previousHome;
+  if (testDir) rmSync(testDir, { recursive: true, force: true });
+});
 
 async function readLogs(): Promise<Array<Record<string, any>>> {
   const url = new URL("http://localhost/api/logs");
@@ -154,5 +175,33 @@ describe("GET /api/logs display metrics", () => {
     const [dto] = await readLogs();
     expect(dto!.displayMetrics.cost).toEqual({ kind: "unavailable", reason: "invalid_cache_breakdown" });
   });
+
+  test("fixture usage rows land in the scratch home, never the default location", () => {
+    // Pins the safety property this file's isolation exists for: addRequestLog
+    // persists to usage.jsonl, so if the scratch-home hook is ever dropped (or a
+    // future test logs before it runs), a bare `bun test <file>` from outside the
+    // repo writes fixture rows into the developer's real ~/.opencodex log.
+    const requestId = "safety-pin-usage-log-target";
+    addRequestLog(baseEntry({ requestId }));
+
+    const resolvedTarget = usageLogPath();
+    expect(resolvedTarget).toBe(join(testDir, "usage.jsonl"));
+    expect(readFileSync(resolvedTarget, "utf-8")).toContain(requestId);
+
+    // The default location (what the resolver returns with no OPENCODEX_HOME
+    // override) must never be the write target for this suite.
+    const previousHome = process.env.OPENCODEX_HOME;
+    delete process.env.OPENCODEX_HOME;
+    try {
+      const defaultTarget = usageLogPath();
+      expect(defaultTarget).not.toBe(resolvedTarget);
+      if (existsSync(defaultTarget)) {
+        expect(readFileSync(defaultTarget, "utf-8")).not.toContain(requestId);
+      }
+    } finally {
+      if (previousHome === undefined) delete process.env.OPENCODEX_HOME;
+      else process.env.OPENCODEX_HOME = previousHome;
+    }
+  });
 });
 import { ManagementRequest as Request } from "./helpers/management-auth";