persist node ids in .cache

brings back EXO_CACHE_HOME as always ~/.cache/exo/, and store the node
id in there. no random copies now!

src/exo/routing/router.py

@@ -234,8 +234,6 @@ def get_node_id_keypair(
     Obtains the :class:`Keypair` associated with this node-ID.
     Obtain the :class:`PeerId` by from it.
     """
-    # TODO(evan): bring back node id persistence once we figure out how to deal with duplicates
-    return Keypair.generate()
 
     def lock_path(path: str | bytes | PathLike[str] | PathLike[bytes]) -> Path:
         return Path(str(path) + ".lock")
@@ -255,6 +253,6 @@ def get_node_id_keypair(
 
         # if no valid credentials, create new ones and persist
         with open(path, "w+b") as f:
-            keypair = Keypair.generate_ed25519()
+            keypair = Keypair.generate()
             f.write(keypair.to_bytes())
             return keypair

src/exo/shared/constants.py

@@ -8,12 +8,12 @@ _EXO_HOME_ENV = os.environ.get("EXO_HOME", None)
 
 
 def _get_xdg_dir(env_var: str, fallback: str) -> Path:
-    """Get XDG directory, prioritising EXO_HOME environment variable if its set. On non-Linux platforms, default to ~/.exo."""
+    """Get XDG directory, prioritising EXO_HOME environment variable if its set. On non-Linux platforms, default to ~/.exo. Cache home always prefers .cache/exo"""
 
     if _EXO_HOME_ENV is not None:
         return Path.home() / _EXO_HOME_ENV
 
-    if sys.platform != "linux":
+    if sys.platform != "linux" and env_var != "XDG_CACHE_HOME":
         return Path.home() / ".exo"
 
     xdg_value = os.environ.get(env_var, None)
@@ -54,10 +54,9 @@ DASHBOARD_DIR = (
 # Log files (data/logs or cache)
 EXO_LOG_DIR = EXO_CACHE_HOME / "exo_log"
 EXO_LOG = EXO_LOG_DIR / "exo.log"
-EXO_TEST_LOG = EXO_CACHE_HOME / "exo_test.log"
 
 # Identity (config)
-EXO_NODE_ID_KEYPAIR = EXO_CONFIG_HOME / "node_id.keypair"
+EXO_NODE_ID_KEYPAIR = EXO_CACHE_HOME / "node_id.keypair"
 EXO_CONFIG_FILE = EXO_CONFIG_HOME / "config.toml"
 
 # libp2p topics for event forwarding

src/exo/shared/tests/test_xdg_paths.py

@@ -94,7 +94,27 @@ def test_macos_uses_traditional_paths():
         home = Path.home()
         assert home / ".exo" == constants.EXO_CONFIG_HOME
         assert home / ".exo" == constants.EXO_DATA_HOME
-        assert home / ".exo" == constants.EXO_CACHE_HOME
+        assert home / ".cache" / "exo" == constants.EXO_CACHE_HOME
+
+
+def test_exo_home_env():
+    """Test that macOS uses traditional ~/.exo directory."""
+    # Remove EXO_HOME to ensure we test the default behavior
+    env = {k: v for k, v in os.environ.items() if k != "EXO_HOME"}
+    env["EXO_HOME"] = "/exo"
+    with (
+        mock.patch.dict(os.environ, env, clear=True),
+        mock.patch.object(sys, "platform", "darwin"),
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        assert Path("/exo") == constants.EXO_CONFIG_HOME
+        assert Path("/exo") == constants.EXO_DATA_HOME
+        assert Path("/exo") == constants.EXO_CACHE_HOME
 
 
 def test_node_id_in_config_dir():

src/exo/worker/engines/mlx/utils_mlx.py

@@ -2,6 +2,7 @@ import json
 import os
 import re
 import sys
+import tempfile
 import time
 from pathlib import Path
 from typing import Any, cast
@@ -98,14 +99,13 @@ def mlx_distributed_init(
     rank = bound_instance.bound_shard.device_rank
     logger.info(f"Starting initialization for rank {rank}")
 
-    coordination_file = None
-    try:
+    with tempfile.TemporaryDirectory() as tmpdir:
+        coordination_file = str(
+            Path(tmpdir) / f"hosts_{bound_instance.instance.instance_id}_{rank}.json"
+        )
         # TODO: singleton instances
         match bound_instance.instance:
             case MlxRingInstance(hosts_by_node=hosts_by_node, ephemeral_port=_):
-                coordination_file = (
-                    f"./hosts_{bound_instance.instance.instance_id}_{rank}.json"
-                )
                 hosts_for_node = hosts_by_node[bound_instance.bound_node_id]
                 hosts_json = HostList.from_hosts(hosts_for_node).model_dump_json()
 
@@ -128,9 +128,6 @@ def mlx_distributed_init(
                     jaccl_devices[i][i] is None for i in range(len(jaccl_devices))
                 )
                 # Use RDMA connectivity matrix
-                coordination_file = (
-                    f"./hosts_{bound_instance.instance.instance_id}_{rank}.json"
-                )
                 jaccl_devices_json = json.dumps(jaccl_devices)
 
                 with open(coordination_file, "w") as f:
@@ -150,10 +147,6 @@ def mlx_distributed_init(
         logger.info(f"Rank {rank} mlx distributed initialization complete")
 
         return group
-    finally:
-        with contextlib.suppress(FileNotFoundError):
-            if coordination_file:
-                os.remove(coordination_file)
 
 
 def initialize_mlx(