ci: clean up backend test processes on cancel [CI]

ci/run-with-timeout.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+"""Run a command in its own process group and clean it up on timeout/cancel."""
+
+from __future__ import annotations
+
+import os
+import signal
+import subprocess
+import sys
+import time
+
+
+GRACE_SECONDS = 10
+
+
+def main() -> int:
+    if len(sys.argv) < 3:
+        print("usage: run-with-timeout.py <seconds> <command> [args...]", file=sys.stderr)
+        return 2
+
+    try:
+        timeout_seconds = float(sys.argv[1])
+    except ValueError:
+        print("timeout must be a number of seconds", file=sys.stderr)
+        return 2
+
+    process = subprocess.Popen(sys.argv[2:], start_new_session=True)
+    stop_signal: int | None = None
+    stop_started: float | None = None
+    timed_out = False
+
+    def request_stop(signum: int, _frame: object) -> None:
+        nonlocal stop_signal, stop_started
+        if stop_signal is None:
+            stop_signal = signum
+            stop_started = time.monotonic()
+            try:
+                os.killpg(process.pid, signal.SIGTERM)
+            except ProcessLookupError:
+                pass
+
+    for signum in (signal.SIGTERM, signal.SIGINT, signal.SIGHUP):
+        signal.signal(signum, request_stop)
+
+    deadline = time.monotonic() + timeout_seconds
+    while True:
+        now = time.monotonic()
+        if stop_signal is None and not timed_out and now >= deadline:
+            timed_out = True
+            stop_started = now
+            try:
+                os.killpg(process.pid, signal.SIGTERM)
+            except ProcessLookupError:
+                pass
+        elif stop_started is not None and now - stop_started >= GRACE_SECONDS:
+            try:
+                os.killpg(process.pid, signal.SIGKILL)
+            except ProcessLookupError:
+                pass
+            stop_started = None
+
+        try:
+            result = process.wait(timeout=0.2)
+            if stop_signal is not None:
+                try:
+                    os.killpg(process.pid, signal.SIGKILL)
+                except ProcessLookupError:
+                    pass
+                return 128 + stop_signal
+            if timed_out:
+                try:
+                    os.killpg(process.pid, signal.SIGKILL)
+                except ProcessLookupError:
+                    pass
+                return 124
+            return result
+        except subprocess.TimeoutExpired:
+            continue
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())