diff --git a/scripts/long_task_governor_wrapper.mjs b/scripts/long_task_governor_wrapper.mjs
index 45c897c..2aff442 100644
--- a/scripts/long_task_governor_wrapper.mjs
+++ b/scripts/long_task_governor_wrapper.mjs
@@ -1,12 +1,25 @@
 #!/usr/bin/env node
 import fs from 'fs';
 
+function fail(code, message) {
+  process.stderr.write(`${code}: ${message}\n`);
+  process.exit(1);
+}
+
 function parseArgs(argv) {
   const args = { input: '', pretty: true };
   for (let i = 2; i < argv.length; i += 1) {
     const arg = argv[i];
-    if (arg === '--input') args.input = argv[++i] || '';
-    else if (arg === '--compact') args.pretty = false;
+    if (arg === '--input') {
+      const value = argv[i + 1];
+      if (!value || value.startsWith('--')) fail('CLI_ERROR', '--input requires a value');
+      args.input = value;
+      i += 1;
+    } else if (arg === '--compact') {
+      args.pretty = false;
+    } else {
+      fail('CLI_ERROR', `unknown argument: ${arg}`);
+    }
   }
   return args;
 }
@@ -17,7 +30,13 @@ function readInput(path) {
 }
 
 function normalizeRequest(raw) {
-  const data = JSON.parse(raw);
+  let data;
+  try {
+    data = JSON.parse(raw);
+  } catch {
+    fail('INVALID_JSON', 'input must be valid JSON');
+  }
+
   return {
     requestText: data.requestText || '',
     hasFilesOrSystems: Boolean(data.hasFilesOrSystems),
@@ -155,4 +174,8 @@ function main() {
   process.stdout.write(JSON.stringify(output, null, args.pretty ? 2 : 0) + '\n');
 }
 
-main();
+try {
+  main();
+} catch (error) {
+  fail('CLI_ERROR', error && error.message ? error.message : 'unexpected error');
+}
diff --git a/scripts/test_long_task_governor_wrapper.mjs b/scripts/test_long_task_governor_wrapper.mjs
index af20580..d38bcd1 100644
--- a/scripts/test_long_task_governor_wrapper.mjs
+++ b/scripts/test_long_task_governor_wrapper.mjs
@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 import assert from 'node:assert/strict';
-import { execFileSync } from 'node:child_process';
+import { execFileSync, spawnSync } from 'node:child_process';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
 
@@ -102,8 +102,25 @@ function runFixture(fixture) {
   };
 }
 
+function assertErrorCase(name, args, expectedStderr, input) {
+  const result = spawnSync(process.execPath, [wrapperPath, ...args], {
+    cwd: repoRoot,
+    encoding: 'utf8',
+    input,
+  });
+
+  assert.notEqual(result.status, 0, `${name}: expected non-zero exit`);
+  assert.equal(result.stdout, '', `${name}: expected empty stdout`);
+  assert.equal(result.stderr.trim(), expectedStderr, `${name}: unexpected stderr`);
+}
+
 function main() {
   const results = fixtures.map(runFixture);
+
+  assertErrorCase('invalid json', ['--compact'], 'INVALID_JSON: input must be valid JSON', 'not-json\n');
+  assertErrorCase('missing input value', ['--input'], 'CLI_ERROR: --input requires a value');
+  assertErrorCase('unknown argument', ['--bogus'], 'CLI_ERROR: unknown argument: --bogus');
+
   const summary = {
     passed: results.length,
     fixtures: results.map(({ name, output }) => ({
@@ -114,6 +131,7 @@ function main() {
       requiredNextAction: output.requiredNextAction,
       handoffMode: output.handoff.mode,
     })),
+    errorCases: 3,
   };
 
   process.stdout.write(JSON.stringify(summary, null, 2) + '\n');