fix: --no-downloads no longer blocks model loading (#1510)

When --no-downloads is passed, skip download checks in plan() so
pre-staged models can be loaded without DownloadCompleted events.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/exo/main.py

@@ -94,6 +94,7 @@ class Node:
                 command_sender=router.sender(topics.COMMANDS),
                 download_command_sender=router.sender(topics.DOWNLOAD_COMMANDS),
                 event_index_counter=event_index_counter,
+                no_downloads=args.no_downloads,
             )
         else:
             worker = None
@@ -225,6 +226,7 @@ class Node:
                         )
                         self._tg.start_soon(self.download_coordinator.run)
                     if self.worker:
+                        no_downloads = self.worker.no_downloads
                         self.worker.shutdown()
                         # TODO: add profiling etc to resource monitor
                         self.worker = Worker(
@@ -239,6 +241,7 @@ class Node:
                                 topics.DOWNLOAD_COMMANDS
                             ),
                             event_index_counter=self.event_index_counter,
+                            no_downloads=no_downloads,
                         )
                         self._tg.start_soon(self.worker.run)
                     if self.api:

src/exo/worker/main.py

@@ -65,6 +65,7 @@ class Worker:
         command_sender: Sender[ForwarderCommand],
         download_command_sender: Sender[ForwarderDownloadCommand],
         event_index_counter: Iterator[int],
+        no_downloads: bool = False,
     ):
         self.node_id: NodeId = node_id
         self.session_id: SessionId = session_id
@@ -74,6 +75,7 @@ class Worker:
         self.event_index_counter = event_index_counter
         self.command_sender = command_sender
         self.download_command_sender = download_command_sender
+        self.no_downloads = no_downloads
         self.event_buffer = OrderedBuffer[Event]()
         self.out_for_delivery: dict[EventId, ForwarderEvent] = {}
 
@@ -182,6 +184,7 @@ class Worker:
                 self.state.tasks,
                 self.input_chunk_buffer,
                 self.input_chunk_counts,
+                no_downloads=self.no_downloads,
             )
             if task is None:
                 continue

src/exo/worker/plan.py

@@ -51,15 +51,20 @@ def plan(
     tasks: Mapping[TaskId, Task],
     input_chunk_buffer: Mapping[CommandId, dict[int, str]] | None = None,
     input_chunk_counts: Mapping[CommandId, int] | None = None,
+    no_downloads: bool = False,
 ) -> Task | None:
     # Python short circuiting OR logic should evaluate these sequentially.
     return (
         _cancel_tasks(runners, tasks)
         or _kill_runner(runners, all_runners, instances)
         or _create_runner(node_id, runners, instances)
-        or _model_needs_download(node_id, runners, global_download_status)
+        or (
+            None
+            if no_downloads
+            else _model_needs_download(node_id, runners, global_download_status)
+        )
         or _init_distributed_backend(runners, all_runners)
-        or _load_model(runners, all_runners, global_download_status)
+        or _load_model(runners, all_runners, global_download_status, no_downloads)
         or _ready_to_warmup(runners, all_runners)
         or _pending_tasks(runners, tasks, all_runners, input_chunk_buffer or {})
     )
@@ -192,22 +197,25 @@ def _load_model(
     runners: Mapping[RunnerId, RunnerSupervisor],
     all_runners: Mapping[RunnerId, RunnerStatus],
     global_download_status: Mapping[NodeId, Sequence[DownloadProgress]],
+    no_downloads: bool = False,
 ) -> LoadModel | None:
     for runner in runners.values():
         instance = runner.bound_instance.instance
         shard_assignments = instance.shard_assignments
 
-        all_local_downloads_complete = all(
-            nid in global_download_status
-            and any(
-                isinstance(dp, DownloadCompleted)
-                and dp.shard_metadata.model_card.model_id == shard_assignments.model_id
-                for dp in global_download_status[nid]
+        if not no_downloads:
+            all_local_downloads_complete = all(
+                nid in global_download_status
+                and any(
+                    isinstance(dp, DownloadCompleted)
+                    and dp.shard_metadata.model_card.model_id
+                    == shard_assignments.model_id
+                    for dp in global_download_status[nid]
+                )
+                for nid in shard_assignments.node_to_runner
             )
-            for nid in shard_assignments.node_to_runner
-        )
-        if not all_local_downloads_complete:
-            continue
+            if not all_local_downloads_complete:
+                continue
 
         is_single_node_instance = len(instance.shard_assignments.runner_to_shard) == 1
         if is_single_node_instance and isinstance(runner.status, RunnerIdle):

src/exo/worker/tests/unittests/test_plan/test_download_and_loading.py

@@ -157,6 +157,41 @@ def test_plan_does_not_request_download_when_shard_already_downloaded():
     assert not isinstance(result, plan_mod.DownloadModel)
 
 
+def test_plan_loads_model_with_no_downloads_flag():
+    """
+    When no_downloads=True, plan() should skip download checks and proceed
+    to load the model even with empty global_download_status.
+    """
+    shard = get_pipeline_shard_metadata(model_id=MODEL_A_ID, device_rank=0)
+    instance = get_mlx_ring_instance(
+        instance_id=INSTANCE_1_ID,
+        model_id=MODEL_A_ID,
+        node_to_runner={NODE_A: RUNNER_1_ID},
+        runner_to_shard={RUNNER_1_ID: shard},
+    )
+    bound_instance = BoundInstance(
+        instance=instance, bound_runner_id=RUNNER_1_ID, bound_node_id=NODE_A
+    )
+    runner = FakeRunnerSupervisor(bound_instance=bound_instance, status=RunnerIdle())
+
+    runners = {RUNNER_1_ID: runner}
+    instances = {INSTANCE_1_ID: instance}
+    all_runners = {RUNNER_1_ID: RunnerIdle()}
+
+    result = plan_mod.plan(
+        node_id=NODE_A,
+        runners=runners,  # type: ignore
+        global_download_status={},
+        instances=instances,
+        all_runners=all_runners,
+        tasks={},
+        no_downloads=True,
+    )
+
+    assert isinstance(result, LoadModel)
+    assert result.instance_id == INSTANCE_1_ID
+
+
 def test_plan_does_not_load_model_until_all_shards_downloaded_globally():
     """
     LoadModel should not be emitted while some shards are still missing from