diff --git a/src/infra/env.test.ts b/src/infra/env.test.ts
index c035103717..ce968a6e47 100644
--- a/src/infra/env.test.ts
+++ b/src/infra/env.test.ts
@@ -2,48 +2,54 @@ import { describe, expect, it } from "vitest";
 import { isTruthyEnvValue, normalizeZaiEnv } from "./env.js";
 
 describe("normalizeZaiEnv", () => {
-  it("copies Z_AI_API_KEY to ZAI_API_KEY when missing", () => {
+  function withZaiEnv(env: { zaiApiKey?: string; legacyZaiApiKey?: string }, run: () => void) {
     const prevZai = process.env.ZAI_API_KEY;
-    const prevZAi = process.env.Z_AI_API_KEY;
-    process.env.ZAI_API_KEY = "";
-    process.env.Z_AI_API_KEY = "zai-legacy";
-
-    normalizeZaiEnv();
-
-    expect(process.env.ZAI_API_KEY).toBe("zai-legacy");
-
-    if (prevZai === undefined) {
+    const prevLegacy = process.env.Z_AI_API_KEY;
+    if (env.zaiApiKey === undefined) {
       delete process.env.ZAI_API_KEY;
     } else {
-      process.env.ZAI_API_KEY = prevZai;
+      process.env.ZAI_API_KEY = env.zaiApiKey;
     }
-    if (prevZAi === undefined) {
+    if (env.legacyZaiApiKey === undefined) {
       delete process.env.Z_AI_API_KEY;
     } else {
-      process.env.Z_AI_API_KEY = prevZAi;
+      process.env.Z_AI_API_KEY = env.legacyZaiApiKey;
     }
+    try {
+      run();
+    } finally {
+      if (prevZai === undefined) {
+        delete process.env.ZAI_API_KEY;
+      } else {
+        process.env.ZAI_API_KEY = prevZai;
+      }
+      if (prevLegacy === undefined) {
+        delete process.env.Z_AI_API_KEY;
+      } else {
+        process.env.Z_AI_API_KEY = prevLegacy;
+      }
+    }
+  }
+
+  it("copies Z_AI_API_KEY to ZAI_API_KEY when missing", () => {
+    withZaiEnv({ zaiApiKey: "", legacyZaiApiKey: "zai-legacy" }, () => {
+      normalizeZaiEnv();
+      expect(process.env.ZAI_API_KEY).toBe("zai-legacy");
+    });
   });
 
   it("does not override existing ZAI_API_KEY", () => {
-    const prevZai = process.env.ZAI_API_KEY;
-    const prevZAi = process.env.Z_AI_API_KEY;
-    process.env.ZAI_API_KEY = "zai-current";
-    process.env.Z_AI_API_KEY = "zai-legacy";
+    withZaiEnv({ zaiApiKey: "zai-current", legacyZaiApiKey: "zai-legacy" }, () => {
+      normalizeZaiEnv();
+      expect(process.env.ZAI_API_KEY).toBe("zai-current");
+    });
+  });
 
-    normalizeZaiEnv();
-
-    expect(process.env.ZAI_API_KEY).toBe("zai-current");
-
-    if (prevZai === undefined) {
-      delete process.env.ZAI_API_KEY;
-    } else {
-      process.env.ZAI_API_KEY = prevZai;
-    }
-    if (prevZAi === undefined) {
-      delete process.env.Z_AI_API_KEY;
-    } else {
-      process.env.Z_AI_API_KEY = prevZAi;
-    }
+  it("ignores blank legacy Z_AI_API_KEY values", () => {
+    withZaiEnv({ zaiApiKey: "", legacyZaiApiKey: "   " }, () => {
+      normalizeZaiEnv();
+      expect(process.env.ZAI_API_KEY).toBe("");
+    });
   });
 });