fix(lease-broker): recovery_runtime_unittest wait_ready() connect-probe (co-equal CI flake, cherry-pick #898) (#900)

Co-authored-by: jason.woltje <jason@diversecanvas.com>
Co-committed-by: jason.woltje <jason@diversecanvas.com>

packages/mosaic/src/lease-broker/recovery_runtime_unittest.py

@@ -62,8 +62,13 @@ def request(socket_path: Path, value: dict[str, object]) -> dict[str, object]:
 def wait_ready(process: subprocess.Popen[str], socket_path: Path) -> None:
     deadline = time.monotonic() + 5.0
     while time.monotonic() < deadline:
-        if socket_path.exists():
+        try:
+            with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as probe:
+                probe.settimeout(0.25)
+                probe.connect(str(socket_path))
             return
+        except (ConnectionRefusedError, FileNotFoundError):
+            pass
         if process.poll() is not None:
             output = process.stdout.read() if process.stdout is not None else ""
             raise RuntimeError(f"daemon exited before READY: {output}")