Fix process tree cancellation for tools

backend/api/server.py

@@ -8,9 +8,11 @@ from __future__ import annotations
 
 import asyncio
 import json
+import os
 import queue
 import re
 import shutil
+import signal
 import threading
 import time
 import venv
@@ -270,7 +272,7 @@ class RunProcessRegistry:
         for process in processes:
             try:
                 if process.poll() is None:
-                    process.terminate()
+                    self._signal_process_tree(process, signal.SIGTERM)
             except OSError:
                 continue
         deadline = time.monotonic() + 1.0
@@ -279,11 +281,35 @@ class RunProcessRegistry:
                 remaining = max(0.0, deadline - time.monotonic())
                 process.wait(timeout=remaining)
             except Exception:
+                self._signal_process_tree(process, signal.SIGKILL)
                 try:
-                    process.kill()
-                except OSError:
+                    process.wait(timeout=1.0)
+                except Exception:
                     pass
 
+    @staticmethod
+    def _signal_process_tree(process: Any, sig: signal.Signals) -> None:
+        try:
+            if os.name == 'posix':
+                pgid = os.getpgid(process.pid)
+                if pgid == process.pid:
+                    os.killpg(pgid, sig)
+                    return
+            if sig == signal.SIGTERM:
+                process.terminate()
+            else:
+                process.kill()
+        except ProcessLookupError:
+            return
+        except OSError:
+            try:
+                if sig == signal.SIGTERM:
+                    process.terminate()
+                else:
+                    process.kill()
+            except OSError:
+                pass
+
 
 @dataclass
 class RunRecord: