add ptyc spawn test to toolchain category

Sends a valid JSON request to ptyc via stdin, verifies it parses the
request (exit 2 = syscall failed, not exit 1 = bad request). Full PTY
setup needs socketpair/SCM_RIGHTS which only PtySession provides.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.pql/pql-plan.json

@@ -1,5 +1,5 @@
 {
-  "exported_at": "2026-04-26T12:16:59Z",
+  "exported_at": "2026-04-26T13:07:25Z",
   "decisions": [
     {
       "id": "D-1",

lib/test_app.dart

@@ -173,6 +173,17 @@ class _ClideTestAppState extends State<ClideTestApp> {
       return 'exit=${r.exitCode} ${(r.stdout as String).trim()}';
     });
 
+    // ptyc stdin/stdout test — send a valid request, verify JSON response
+    await _testAsync('ptyc spawn echo', () async {
+      final proc = await Process.start(tc.ptyc, []);
+      // Send a request for /bin/echo — simplest possible child
+      proc.stdin.write('{"argv":["/bin/echo","hello"],"cwd":"/tmp","env":{},"cols":80,"rows":24}');
+      await proc.stdin.close();
+      final stdout = await proc.stdout.transform(const SystemEncoding().decoder).join();
+      final exitCode = await proc.exitCode;
+      return 'exit=$exitCode stdout=${stdout.trim().split('\n').first}';
+    });
+
     print('[testmode]');
   }