diff --git a/package-lock.json b/package-lock.json
index 2aad6f7..eb83d6b 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -20,7 +20,7 @@
         "markdownlint-cli2": "^0.22.0",
         "tsup": "^8.0.2",
         "tsx": "^4.7.1",
-        "typescript": "^5.9.3",
+        "typescript": "^6.0.3",
         "vitest": "^4.1.2"
       },
       "engines": {
@@ -3277,9 +3277,9 @@
       }
     },
     "node_modules/postcss": {
-      "version": "8.5.8",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.8.tgz",
-      "integrity": "sha512-OW/rX8O/jXnm82Ey1k44pObPtdblfiuWnrd8X7GJ7emImCOstunGbXUpp7HdBrFQX6rJzn3sPT397Wp5aCwCHg==",
+      "version": "8.5.10",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.10.tgz",
+      "integrity": "sha512-pMMHxBOZKFU6HgAZ4eyGnwXF/EvPGGqUr0MnZ5+99485wwW41kW91A4LOGxSHhgugZmSChL5AlElNdwlNgcnLQ==",
       "dev": true,
       "funding": [
         {
@@ -3825,9 +3825,9 @@
       }
     },
     "node_modules/typescript": {
-      "version": "5.9.3",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
-      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "version": "6.0.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-6.0.3.tgz",
+      "integrity": "sha512-y2TvuxSZPDyQakkFRPZHKFm+KKVqIisdg9/CZwm9ftvKXLP8NRWj38/ODjNbr43SsoXqNuAisEf1GdCxqWcdBw==",
       "dev": true,
       "license": "Apache-2.0",
       "bin": {
@@ -4112,4 +4112,4 @@
       }
     }
   }
-}
\ No newline at end of file
+}
diff --git a/package.json b/package.json
index c9ddd4a..1b0579d 100644
--- a/package.json
+++ b/package.json
@@ -64,7 +64,7 @@
     "markdownlint-cli2": "^0.22.0",
     "tsup": "^8.0.2",
     "tsx": "^4.7.1",
-    "typescript": "^5.9.3",
+    "typescript": "^6.0.3",
     "vitest": "^4.1.2"
   },
   "license": "Apache-2.0",
diff --git a/src/cli.ts b/src/cli.ts
index 2b800f0..4f9bc4e 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -1021,9 +1021,11 @@ function exitWithStartupError(error: CliError): never {
       process.stdout.write(`${JSON.stringify(payload)}\n`);
     }
     process.exit(error.exitCode);
+    throw new Error("Unreachable after process.exit");
   }
   process.stderr.write(`${error.message}\n`);
   process.exit(error.exitCode);
+  throw new Error("Unreachable after process.exit");
 }
 
 function writeOutputOrThrow(content: string, output?: string): void {
@@ -1064,6 +1066,7 @@ function emitUnhandledCliError(error: unknown): never {
       process.stdout.write(`${JSON.stringify(payload)}\n`);
     }
     process.exit(resolved.exitCode);
+    throw new Error("Unreachable after process.exit");
   }
 
   // Non-JSON mode: agent formatting or plain text
@@ -1071,10 +1074,12 @@ function emitUnhandledCliError(error: unknown): never {
     const help = getErrorHelp(resolved.code, resolved.message);
     process.stderr.write(`${formatAgentError(help, true)}\n`);
     process.exit(resolved.exitCode);
+    throw new Error("Unreachable after process.exit");
   }
 
   process.stderr.write(`${resolved.message}\n`);
   process.exit(resolved.exitCode);
+  throw new Error("Unreachable after process.exit");
 }
 
 const startupArgv = hideBin(process.argv);
@@ -1143,7 +1148,7 @@ cli
   .option("timeout", { type: "number", default: 15000 })
   .option("retries", { type: "number", default: 2 })
   .option("retry-backoff", { type: "number", default: 400 })
-  .check((args) => {
+  .check((args: Arguments) => {
     const globals = args as unknown as CliGlobals;
     // Always validate URL format (not just when network is enabled)
     // This catches invalid URLs even in preview mode
@@ -1738,7 +1743,7 @@ cli
   .recommendCommands()
   .demandCommand(1)
   .exitProcess(false)
-  .fail((msg, err, y) => {
+  .fail((msg: string | null | undefined, err: Error | undefined, y: Argv) => {
     const message = err?.message ?? msg ?? "Unexpected error";
     const isUsageError =
       !err || (err as { name?: string }).name === "YError" || (err instanceof CliError && err.exitCode === 2);
@@ -1784,4 +1789,4 @@ void (async () => {
   } catch (error) {
     emitUnhandledCliError(error);
   }
-})();
\ No newline at end of file
+})();
diff --git a/src/output.ts b/src/output.ts
index 6b745a6..a40de46 100644
--- a/src/output.ts
+++ b/src/output.ts
@@ -100,7 +100,7 @@ function resolveCliVersion(): string {
   const envVersion = process.env.npm_package_version?.trim();
   if (envVersion) {
     cachedVersion = envVersion;
-    return cachedVersion;
+    return envVersion;
   }
 
   try {
@@ -109,8 +109,9 @@ function resolveCliVersion(): string {
     const raw = fs.readFileSync(packagePath, "utf8");
     const parsed = JSON.parse(raw) as { version?: string };
     if (parsed.version && parsed.version.trim().length > 0) {
-      cachedVersion = parsed.version.trim();
-      return cachedVersion;
+      const packageVersion = parsed.version.trim();
+      cachedVersion = packageVersion;
+      return packageVersion;
     }
   } catch (error) {
     // no-op: fall back to default version
diff --git a/tsconfig.json b/tsconfig.json
index bedfd8d..15807f8 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -10,7 +10,8 @@
     "exactOptionalPropertyTypes": true,
     "esModuleInterop": true,
     "skipLibCheck": true,
-    "forceConsistentCasingInFileNames": true
+    "forceConsistentCasingInFileNames": true,
+    "types": ["node"]
   },
   "include": ["src", "tests"]
 }