fix

## Motivation

Coordination files for MLX distributed init were written to the current
working directory (./hosts_*.json)

## Changes

- Move coordination file creation to a tempfile.TemporaryDirectory(),
which auto-cleans on context manager exit

src/exo/master/api.py

@@ -524,15 +524,15 @@ class API:
 
             if (
                 model_card.model_id,
-                sharding,
+                instance.sharding(),
-                instance_meta,
+                instance.instance_meta(),
                 len(placement_node_ids),
             ) not in seen:
                 previews.append(
                     PlacementPreview(
                         model_id=model_card.model_id,
-                        sharding=sharding,
+                        sharding=instance.sharding(),
-                        instance_meta=instance_meta,
+                        instance_meta=instance.instance_meta(),
                         instance=instance,
                         memory_delta_by_node=memory_delta_by_node or None,
                         error=None,
@@ -541,8 +541,8 @@ class API:
             seen.add(
                 (
                     model_card.model_id,
-                    sharding,
+                    instance.sharding(),
-                    instance_meta,
+                    instance.instance_meta(),
                     len(placement_node_ids),
                 )
             )

src/exo/shared/types/worker/instances.py

@@ -4,7 +4,13 @@ from pydantic import model_validator
 
 from exo.shared.models.model_cards import ModelTask
 from exo.shared.types.common import Host, Id, NodeId
-from exo.shared.types.worker.runners import RunnerId, ShardAssignments, ShardMetadata
+from exo.shared.types.worker.runners import RunnerId, ShardAssignments
+from exo.shared.types.worker.shards import (
+    PipelineShardMetadata,
+    Sharding,
+    ShardMetadata,
+    TensorShardMetadata,
+)
 from exo.utils.pydantic_ext import CamelCaseModel, TaggedModel
 
 
@@ -24,16 +30,40 @@ class BaseInstance(TaggedModel):
     def shard(self, runner_id: RunnerId) -> ShardMetadata | None:
         return self.shard_assignments.runner_to_shard.get(runner_id, None)
 
+    @staticmethod
+    def instance_meta() -> InstanceMeta: ...
+
+    def sharding(self) -> Sharding:
+        if all(
+            isinstance(sm, PipelineShardMetadata)
+            for sm in self.shard_assignments.runner_to_shard.values()
+        ):
+            return Sharding.Pipeline
+        if all(
+            isinstance(sm, TensorShardMetadata)
+            for sm in self.shard_assignments.runner_to_shard.values()
+        ):
+            return Sharding.Tensor
+        raise ValueError("shard metadata malformed")
+
 
 class MlxRingInstance(BaseInstance):
     hosts_by_node: dict[NodeId, list[Host]]
     ephemeral_port: int
 
+    @staticmethod
+    def instance_meta() -> InstanceMeta:
+        return InstanceMeta.MlxRing
+
 
 class MlxJacclInstance(BaseInstance):
     jaccl_devices: list[list[str | None]]
     jaccl_coordinators: dict[NodeId, str]
 
+    @staticmethod
+    def instance_meta() -> InstanceMeta:
+        return InstanceMeta.MlxJaccl
+
 
 # TODO: Single node instance
 Instance = MlxRingInstance | MlxJacclInstance

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
+    with tempfile.TemporaryDirectory() as tmpdir:
-    try:
+        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(