Fix: forward engine exit code from impeccable.cmd (#836)

Bare `exit /b` dropped the process code when the launcher was cmd /c's entry point (PowerShell, Node spawn), so Windows skill runs treated detector findings as success.

AI assistance: implemented by Cursor Grok 4.6.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/skills/tests/launcher_contract_tests.rs

@@ -57,6 +57,28 @@ fn cmd_launcher_asset_naming_matches_engine() {
     assert!(!cmd.contains("npm i -g"));
 }
 
+#[test]
+fn cmd_launcher_forwards_engine_exit_code() {
+    // Bare `exit /b` drops the process exit code when this file is cmd.exe's
+    // entry point (cmd /c, PowerShell, Node spawn). Forward %errorlevel%
+    // after each engine invocation instead.
+    let cmd = launcher_file("impeccable.cmd");
+    for (i, line) in cmd.lines().enumerate() {
+        assert_ne!(
+            line.trim(),
+            "exit /b",
+            "impeccable.cmd line {}: bare exit /b drops the process code: {line}",
+            i + 1
+        );
+    }
+    let forward = "exit /b %errorlevel%";
+    assert_eq!(
+        cmd.matches(forward).count(),
+        2,
+        "PATH candidate and :run must both forward the engine exit code"
+    );
+}
+
 #[test]
 fn cmd_launcher_has_no_multiline_parenthesized_blocks() {
     // cmd.exe expands %var% inside a parenthesized block at parse time, so a

skill/scripts/impeccable.cmd

@@ -59,7 +59,7 @@ if errorlevel 1 goto download
 call :probe impeccable
 if not "%probe_ok%"=="1" goto download
 impeccable %*
-exit /b
+exit /b %errorlevel%
 
 :download
 rem Last resort: fetch this version's binary from the release channel into
@@ -166,7 +166,7 @@ exit /b 127
 
 :run
 "%run%" %*
-exit /b
+exit /b %errorlevel%
 
 :probe
 rem Sets probe_ok=1 when %1 answers the engine handshake: prints

tests/launcher-download.test.mjs

@@ -174,6 +174,34 @@ test('launcher downloads and runs a verified executable', async t => {
   assert.equal(result.requests.length, 2);
 });
 
+test('cmd launcher forwards engine exit code through cmd /c', { skip: WINDOWS ? false : 'Windows-only cmd /c exit-code forwarding' }, async t => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'impeccable-launcher-exit-'));
+  t.after(() => fs.rmSync(root, { recursive: true, force: true }));
+  const home = path.join(root, 'home');
+  fs.mkdirSync(home);
+  const launcher = path.join(root, 'impeccable.cmd');
+  fs.copyFileSync(path.join(ROOT, 'skill/scripts/impeccable.cmd'), launcher);
+  const env = {
+    PATH: `${process.env.SystemRoot}\\System32;${process.env.SystemRoot}`,
+    HOME: home, USERPROFILE: home, TEMP: root, TMP: root,
+    IMPECCABLE_HOME: path.join(root, 'cache'),
+    IMPECCABLE_BIN: COMSPEC,
+    SystemRoot: process.env.SystemRoot,
+    ComSpec: COMSPEC,
+    PROCESSOR_ARCHITECTURE: 'AMD64',
+  };
+  const run = (args) => new Promise((resolve, reject) => {
+    const child = spawn(COMSPEC, ['/d', '/s', '/c', `""${launcher}" ${args}"`], { env, cwd: root, windowsVerbatimArguments: true, timeout: 20000 });
+    child.on('error', reject);
+    child.on('close', (status, signal) => resolve({ status, signal }));
+  });
+  for (const [args, expected] of [['/c exit 2', 2], ['/c exit 1', 1], ['/c exit 0', 0]]) {
+    const result = await run(args);
+    assert.equal(result.signal, null, JSON.stringify(result));
+    assert.equal(result.status, expected, args);
+  }
+});
+
 for (const scenario of ['removed', 'emptied', 'empty-download', 'no-sidecar', 'empty-sidecar', 'mismatch', 'hash-failure', 'removed-during-hash', 'removed-before-move', 'removed-after-move', 'emptied-after-move', 'move-failure']) {
   test(`launcher refuses ${scenario} with an accurate diagnostic`, async t => {
     const result = await exercise(t, scenario);