diff --git a/package-lock.json b/package-lock.json
index 5bd5344..20a07b5 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,7 +15,7 @@
         "proofdiff": "dist/cli.js"
       },
       "devDependencies": {
-        "@types/node": "^22.0.0",
+        "@types/node": "^26.6.3",
         "typescript": "^5.9.0"
       },
       "engines": {
@@ -69,13 +69,13 @@
       }
     },
     "node_modules/@types/node": {
-      "version": "22.20.1",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-22.20.1.tgz",
-      "integrity": "sha512-EANqOCF9QFyra+4pfxUcX9STKJpCLjMbObVzljIJomAWSnuSIEAvyzEU53GaajbXJEgdh0iEcPL+DGvpUd4k1Q==",
+      "version": "26.6.3",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-26.6.3.tgz",
+      "integrity": "sha512-dsqMQQoeTLqu9wynDD00q573mNzso3IdQOAfHRJqLCcmCFPoGo9A1bDpUcv/9tnKpErQWv9uKeGfl37EIS02Yg==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
-        "undici-types": "~6.21.0"
+        "undici-types": "~8.9.0"
       }
     },
     "node_modules/typescript": {
@@ -93,9 +93,9 @@
       }
     },
     "node_modules/undici-types": {
-      "version": "6.21.0",
-      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
-      "integrity": "sha512-iwDZqg0QAGrg9Rav5H4n0M64c3mkR59cJ6wQp+7C4nI0gsmExaedaYLNO44eT4AtBBwjbTiGPMlt2Md0T9H9JQ==",
+      "version": "8.9.0",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-8.9.0.tgz",
+      "integrity": "sha512-KTDyRTYX8sWmKXAikPHHSyc63CRPETMctyjKFupcC6OBLXT3xsN0e9aF7m+mIXutFWpUXuedtowG7iLOzp0kQg==",
       "dev": true,
       "license": "MIT"
     }
diff --git a/package.json b/package.json
index 53bbaba..3d1c5e5 100644
--- a/package.json
+++ b/package.json
@@ -66,7 +66,7 @@
     "@babel/parser": "^7.28.0"
   },
   "devDependencies": {
-    "@types/node": "^22.0.0",
+    "@types/node": "^26.6.3",
     "typescript": "^5.9.0"
   }
 }
diff --git a/tests/analyze.test.ts b/tests/analyze.test.ts
index 5f157fa..6d156b5 100644
--- a/tests/analyze.test.ts
+++ b/tests/analyze.test.ts
@@ -130,7 +130,7 @@ test("passing related test evidence produces a qualified verified status", async
   context.after(() => rm(root, { recursive: true, force: true }));
   await writeFiles(root, { "src/math.js": "export function add(a, b) { return a + b + 0; }\n" });
   const report = await analyzeRepository({ repo: root, runChecks: true, timeoutMs: 20_000 });
-  assert.equal(report.checks[0]?.status, "passed", report.checks[0]?.output);
+  assert.equal(report.checks[0]?.status, "passed", report.checks[0]?.output ?? "");
   assert.ok(report.checks.some((check) => check.id.endsWith(":targeted") && check.status === "passed"));
   assert.equal(report.assessments[0]?.status, "verified");
   assert.equal(report.summary.overallStatus, "verified");
@@ -242,7 +242,7 @@ test("unattributed unittest failures cannot hide behind an unavailable batch tar
   const observations = new Map(targeted?.targetObservations?.map((observation) => [observation.path, observation]));
   const sourceA = report.assessments.find((assessment) => assessment.file.path === "src/a.py");
 
-  assert.equal(targeted?.status, "failed", targeted?.output);
+  assert.equal(targeted?.status, "failed", targeted?.output ?? "");
   assert.equal(observations.get("tests/test_a.py")?.outcome, "not-observed");
   assert.match(observations.get("tests/test_a.py")?.detail ?? "", /unattributed process-level failure/);
   assert.equal(observations.get("tests/test_b.py")?.outcome, "failed");
diff --git a/tests/checks.test.ts b/tests/checks.test.ts
index c6d6307..5091ee7 100644
--- a/tests/checks.test.ts
+++ b/tests/checks.test.ts
@@ -340,7 +340,7 @@ test("stdlib unittest projects use unittest without requiring pytest", async (co
   const { checks } = await discoverChecks(root);
   assert.deepEqual(checks.map((check) => check.id), ["python:test:unittest"]);
   const [result] = await runChecks(root, checks, { timeoutMs: 10_000, maxOutputBytes: 10_000 });
-  assert.equal(result?.status, "passed", result?.output);
+  assert.equal(result?.status, "passed", result?.output ?? "");
 });
 
 test("checks receive no inherited application secrets", async (context) => {