Fix code execution PTY reset hangs

Start local PTY shells in a new process session and make close() escalate from SIGTERM to SIGKILL when a foreground command refuses to exit. This keeps code_execution_tool reset from blocking indefinitely on stuck terminal processes.\n\nAdd regression coverage for closing a TERM-resistant shell and document the reset lifecycle contract.

plugins/_code_execution/AGENTS.md

@@ -14,6 +14,7 @@
 ## Local Contracts
 
 - Keep session concurrency, timeout, streaming, and reset behavior predictable.
+- Terminal reset/close must not hang on foreground commands or shells that ignore SIGTERM.
 - Explicitly target local versus SSH execution runtimes.
 - Do not hardcode secrets, SSH credentials, or local user paths.
 

plugins/_code_execution/helpers/tty_session.py

@@ -1,10 +1,12 @@
-import asyncio, os, sys, platform, errno
+import asyncio, os, sys, platform, errno, signal
 
 _IS_WIN = platform.system() == "Windows"
 if _IS_WIN:
     import winpty  # pip install pywinpty # type: ignore
     import msvcrt
 
+_CLOSE_TIMEOUT_SECONDS = 2
+
 
 def _reconfigure_stream_errors(stream) -> None:
     reconfigure = getattr(stream, "reconfigure", None)
@@ -77,15 +79,16 @@ class TTYSession:
 
         # Terminate the process if it exists
         if self._proc:
+            if getattr(self._proc, "returncode", None) is None:
+                self._signal_process(signal.SIGTERM)
             try:
-                if getattr(self._proc, "returncode", None) is None:
-                    self._proc.terminate()
-            except ProcessLookupError:
-                pass
-            except Exception:
-                pass
-            try:
-                await self._proc.wait()
+                await asyncio.wait_for(self._proc.wait(), _CLOSE_TIMEOUT_SECONDS)
+            except asyncio.TimeoutError:
+                self._signal_process(signal.SIGKILL)
+                try:
+                    await asyncio.wait_for(self._proc.wait(), _CLOSE_TIMEOUT_SECONDS)
+                except Exception:
+                    pass
             except Exception:
                 pass
 
@@ -93,6 +96,28 @@ class TTYSession:
         self._proc = None
         self._pump_task = None
 
+    def _signal_process(self, sig):
+        if self._proc is None:
+            return
+        try:
+            if _IS_WIN:
+                if sig == signal.SIGKILL:
+                    self._proc.kill()
+                else:
+                    self._proc.terminate()
+                return
+            os.killpg(self._proc.pid, sig)
+        except ProcessLookupError:
+            pass
+        except Exception:
+            try:
+                if sig == signal.SIGKILL:
+                    self._proc.kill()
+                else:
+                    self._proc.terminate()
+            except Exception:
+                pass
+
     def _release_pty_master(self):
         """Release the POSIX PTY master exactly once.
 
@@ -166,11 +191,7 @@ class TTYSession:
 
         # Only attempt to kill if the process is still running
         if getattr(self._proc, "returncode", None) is None:
-            try:
-                self._proc.kill()
-            except ProcessLookupError:
-                # Child already gone – treat as successfully killed
-                pass
+            self._signal_process(signal.SIGKILL)
         self._release_pty_master()
 
     async def read(self, timeout=None):
@@ -241,6 +262,7 @@ async def _spawn_posix_pty(cmd, cwd, env, echo):
         cwd=cwd,
         env=env,
         close_fds=True,
+        start_new_session=True,
     )
     os.close(slave)
 

tests/test_code_execution_pager.py

@@ -1,10 +1,13 @@
-"""Regression tests for issue #1697.
+"""Regression tests for code execution shell lifecycle behavior.
 
 Pagers (more/less) must be disabled in the non-interactive shells created by the
 code execution tool: without user input they block forever and spin at 100% CPU.
 """
 
+import asyncio
+
 from plugins._code_execution.helpers import shell_local, shell_ssh
+from plugins._code_execution.helpers.tty_session import TTYSession
 
 
 def test_local_env_disables_pagers_and_preserves_existing():
@@ -30,3 +33,13 @@ def test_local_env_does_not_mutate_input():
 def test_ssh_command_disables_pagers():
     assert "GIT_PAGER=cat" in shell_ssh.PAGER_DISABLE_COMMAND
     assert "PAGER=cat" in shell_ssh.PAGER_DISABLE_COMMAND
+
+
+def test_tty_close_kills_term_resistant_process():
+    async def run():
+        session = TTYSession("bash -lc 'trap \"\" TERM; sleep 30'")
+        await session.start()
+        await asyncio.wait_for(session.close(), timeout=6)
+        assert session._proc is None
+
+    asyncio.run(run())