diff --git a/tests/tools/test_file_sync_back.py b/tests/tools/test_file_sync_back.py
index 792d4c0f51..5da0886a6c 100644
--- a/tests/tools/test_file_sync_back.py
+++ b/tests/tools/test_file_sync_back.py
@@ -216,7 +216,7 @@ class TestSyncBackConflict:
 class TestSyncBackRetries:
     """Retry behaviour with exponential backoff."""
 
-    @patch("tools.environments.file_sync.time.sleep")
+    @patch("tools.environments.file_sync._sleep")
     def test_sync_back_retries_on_failure(self, mock_sleep, tmp_path):
         call_count = 0
 
@@ -237,7 +237,7 @@ class TestSyncBackRetries:
         mock_sleep.assert_any_call(_SYNC_BACK_BACKOFF[0])
         mock_sleep.assert_any_call(_SYNC_BACK_BACKOFF[1])
 
-    @patch("tools.environments.file_sync.time.sleep")
+    @patch("tools.environments.file_sync._sleep")
     def test_sync_back_all_retries_exhausted(self, mock_sleep, tmp_path, caplog):
         def always_fail(dest: Path):
             raise RuntimeError("persistent failure")
diff --git a/tools/environments/file_sync.py b/tools/environments/file_sync.py
index 0a54cbb85d..742e024ad8 100644
--- a/tools/environments/file_sync.py
+++ b/tools/environments/file_sync.py
@@ -29,6 +29,12 @@ from tools.environments.base import _file_mtime_key
 
 logger = logging.getLogger(__name__)
 
+# Keep retry sleeps patchable without mutating the shared stdlib ``time``
+# module. Patching ``tools.environments.file_sync.time.sleep`` replaces
+# ``time.sleep`` globally because ``time`` is the module object; under xdist
+# that lets unrelated background threads inflate retry-test call counts.
+_sleep = time.sleep
+
 _SYNC_INTERVAL_SECONDS = 5.0
 _FORCE_SYNC_ENV = "HERMES_FORCE_FILE_SYNC"
 
@@ -243,7 +249,7 @@ class FileSyncManager:
                         "sync_back: attempt %d failed (%s), retrying in %ds",
                         attempt + 1, exc, delay,
                     )
-                    time.sleep(delay)
+                    _sleep(delay)
 
         logger.warning("sync_back: all %d attempts failed: %s", _SYNC_BACK_MAX_RETRIES, last_exc)
 
diff --git a/tools/environments/local.py b/tools/environments/local.py
index d419c72c30..3200e63e60 100644
--- a/tools/environments/local.py
+++ b/tools/environments/local.py
@@ -383,6 +383,36 @@ class LocalEnvironment(BaseEnvironment):
 
     def _kill_process(self, proc):
         """Kill the entire process group (all children)."""
+
+        def _group_alive(pgid: int) -> bool:
+            try:
+                # POSIX-only: _IS_WINDOWS is handled before this helper is used.
+                os.killpg(pgid, 0)
+                return True
+            except ProcessLookupError:
+                return False
+            except PermissionError:
+                # The group exists, even if this process cannot signal it.
+                return True
+
+        def _wait_for_group_exit(pgid: int, timeout: float) -> bool:
+            deadline = time.monotonic() + timeout
+            while time.monotonic() < deadline:
+                # Reap the wrapper promptly. A dead but unreaped group leader
+                # still makes killpg(pgid, 0) report the group as alive.
+                try:
+                    proc.poll()
+                except Exception:
+                    pass
+                if not _group_alive(pgid):
+                    return True
+                time.sleep(0.05)
+            try:
+                proc.poll()
+            except Exception:
+                pass
+            return not _group_alive(pgid)
+
         try:
             if _IS_WINDOWS:
                 proc.terminate()
@@ -393,37 +423,29 @@ class LocalEnvironment(BaseEnvironment):
                     pgid = getattr(proc, "_hermes_pgid", None)
                     if pgid is None:
                         raise
-                os.killpg(pgid, signal.SIGTERM)
-                deadline = time.monotonic() + 1.0
-                while time.monotonic() < deadline:
-                    if proc.poll() is not None:
-                        try:
-                            os.killpg(pgid, 0)
-                        except ProcessLookupError:
-                            return
-                    time.sleep(0.05)
 
-                # The shell can exit quickly while a child in the same process
-                # group is still shutting down. Escalate based on the process
-                # group, not just the shell wrapper, so interrupted commands do
-                # not leave orphaned grandchildren under load.
                 try:
-                    # _IS_WINDOWS is guarded by the enclosing else branch.
+                    os.killpg(pgid, signal.SIGTERM)
+                except ProcessLookupError:
+                    return
+
+                # Wait on the process group, not just the shell wrapper. Under
+                # load the wrapper can exit before grandchildren do; returning
+                # at that point leaves orphaned process-group members behind.
+                if _wait_for_group_exit(pgid, 1.0):
+                    return
+
+                try:
+                    # POSIX-only: _IS_WINDOWS is handled by the outer branch.
                     os.killpg(pgid, signal.SIGKILL)
                 except ProcessLookupError:
                     return
+                _wait_for_group_exit(pgid, 2.0)
                 try:
-                    proc.wait(timeout=1.0)
-                except subprocess.TimeoutExpired:
+                    proc.wait(timeout=0.2)
+                except (subprocess.TimeoutExpired, OSError):
                     pass
-                deadline = time.monotonic() + 1.0
-                while time.monotonic() < deadline:
-                    try:
-                        os.killpg(pgid, 0)
-                    except ProcessLookupError:
-                        return
-                    time.sleep(0.05)
-        except (ProcessLookupError, PermissionError):
+        except (ProcessLookupError, PermissionError, OSError):
             try:
                 proc.kill()
             except Exception: