downloads: add download and delete buttons to downloads UI

The downloads page showed model download progress but provided no way
for users to trigger downloads or remove completed models from disk.

Added API endpoints (POST /download/start, DELETE /download/{node_id}/{model_id})
that send StartDownload and DeleteDownload commands via the download_command_sender.
Updated the dashboard downloads page with per-model buttons: a download button
for incomplete downloads and a delete button for completed ones.

This allows users to manage downloads directly from the UI without needing
to trigger downloads through other means.

Test plan:
- Deployed on a 3 machine cluster. Did several downloads/deletions - all
  work and the dashboard updates relatively fluently. It takes roughly 5
  seconds to render a 131GB model deletion which isn't too bad.

dashboard/src/routes/downloads/+page.svelte

@@ -6,6 +6,8 @@
     type DownloadProgress,
     refreshState,
     lastUpdate as lastUpdateStore,
+    startDownload,
+    deleteDownload,
   } from "$lib/stores/app.svelte";
   import HeaderNav from "$lib/components/HeaderNav.svelte";
 
@@ -28,6 +30,7 @@
     etaMs: number;
     status: "completed" | "downloading";
     files: FileProgress[];
+    shardMetadata?: Record<string, unknown>;
   };
 
   type NodeEntry = {
@@ -269,6 +272,12 @@
             }
           }
 
+          // Extract shard_metadata for use with download actions
+          const shardMetadata = (downloadPayload.shard_metadata ??
+            downloadPayload.shardMetadata) as
+            | Record<string, unknown>
+            | undefined;
+
           const entry: ModelEntry = {
             modelId,
             prettyName,
@@ -285,6 +294,7 @@
                 ? "completed"
                 : "downloading",
             files,
+            shardMetadata,
           };
 
           const existing = modelMap.get(modelId);
@@ -469,6 +479,52 @@
                     >
                       {pct.toFixed(1)}%
                     </span>
+                    {#if model.status !== "completed" && model.shardMetadata}
+                      <button
+                        type="button"
+                        class="text-exo-light-gray hover:text-exo-yellow transition-colors"
+                        onclick={() =>
+                          startDownload(node.nodeId, model.shardMetadata!)}
+                        title="Start download"
+                      >
+                        <svg
+                          class="w-4 h-4"
+                          viewBox="0 0 20 20"
+                          fill="none"
+                          stroke="currentColor"
+                          stroke-width="2"
+                        >
+                          <path
+                            d="M10 3v10m0 0l-3-3m3 3l3-3M3 17h14"
+                            stroke-linecap="round"
+                            stroke-linejoin="round"
+                          ></path>
+                        </svg>
+                      </button>
+                    {/if}
+                    {#if model.status === "completed"}
+                      <button
+                        type="button"
+                        class="text-exo-light-gray hover:text-red-400 transition-colors"
+                        onclick={() =>
+                          deleteDownload(node.nodeId, model.modelId)}
+                        title="Delete download"
+                      >
+                        <svg
+                          class="w-4 h-4"
+                          viewBox="0 0 20 20"
+                          fill="none"
+                          stroke="currentColor"
+                          stroke-width="2"
+                        >
+                          <path
+                            d="M4 6h12M8 6V4h4v2m1 0v10a1 1 0 01-1 1H8a1 1 0 01-1-1V6h6"
+                            stroke-linecap="round"
+                            stroke-linejoin="round"
+                          ></path>
+                        </svg>
+                      </button>
+                    {/if}
                     <button
                       type="button"
                       class="text-exo-light-gray hover:text-exo-yellow transition-colors"

src/exo/main.py

@@ -80,6 +80,7 @@ class Node:
                 port=args.api_port,
                 global_event_receiver=router.receiver(topics.GLOBAL_EVENTS),
                 command_sender=router.sender(topics.COMMANDS),
+                download_command_sender=router.sender(topics.DOWNLOAD_COMMANDS),
                 election_receiver=router.receiver(topics.ELECTION_MESSAGES),
             )
         else:

src/exo/master/api.py

@@ -44,6 +44,7 @@ from exo.shared.types.api import (
     ChatCompletionResponse,
     CreateInstanceParams,
     CreateInstanceResponse,
+    DeleteDownloadResponse,
     DeleteInstanceResponse,
     ErrorInfo,
     ErrorResponse,
@@ -61,6 +62,8 @@ from exo.shared.types.api import (
     PlaceInstanceParams,
     PlacementPreview,
     PlacementPreviewResponse,
+    StartDownloadParams,
+    StartDownloadResponse,
     StreamingChoiceResponse,
     ToolCall,
 )
@@ -75,12 +78,16 @@ from exo.shared.types.commands import (
     ChatCompletion,
     Command,
     CreateInstance,
+    DeleteDownload,
     DeleteInstance,
+    DownloadCommand,
     ForwarderCommand,
+    ForwarderDownloadCommand,
     ImageEdits,
     ImageGeneration,
     PlaceInstance,
     SendInputChunk,
+    StartDownload,
     TaskFinished,
 )
 from exo.shared.types.common import CommandId, Id, NodeId, SessionId
@@ -156,12 +163,14 @@ class API:
         # Ideally this would be a MasterForwarderEvent but type system says no :(
         global_event_receiver: Receiver[ForwarderEvent],
         command_sender: Sender[ForwarderCommand],
+        download_command_sender: Sender[ForwarderDownloadCommand],
         # This lets us pause the API if an election is running
         election_receiver: Receiver[ElectionMessage],
     ) -> None:
         self.state = State()
         self._event_log: list[Event] = []
         self.command_sender = command_sender
+        self.download_command_sender = download_command_sender
         self.global_event_receiver = global_event_receiver
         self.election_receiver = election_receiver
         self.event_buffer: OrderedBuffer[Event] = OrderedBuffer[Event]()
@@ -260,6 +269,8 @@ class API:
         self.app.get("/images/{image_id}")(self.get_image)
         self.app.get("/state")(lambda: self.state)
         self.app.get("/events")(lambda: self._event_log)
+        self.app.post("/download/start")(self.start_download)
+        self.app.delete("/download/{node_id}/{model_id:path}")(self.delete_download)
 
     async def place_instance(self, payload: PlaceInstanceParams):
         command = PlaceInstance(
@@ -1292,3 +1303,28 @@ class API:
         await self.command_sender.send(
             ForwarderCommand(origin=self.node_id, command=command)
         )
+
+    async def _send_download(self, command: DownloadCommand):
+        await self.download_command_sender.send(
+            ForwarderDownloadCommand(origin=self.node_id, command=command)
+        )
+
+    async def start_download(
+        self, payload: StartDownloadParams
+    ) -> StartDownloadResponse:
+        command = StartDownload(
+            target_node_id=payload.target_node_id,
+            shard_metadata=payload.shard_metadata,
+        )
+        await self._send_download(command)
+        return StartDownloadResponse(command_id=command.command_id)
+
+    async def delete_download(
+        self, node_id: NodeId, model_id: ModelId
+    ) -> DeleteDownloadResponse:
+        command = DeleteDownload(
+            target_node_id=node_id,
+            model_id=ModelId(model_id),
+        )
+        await self._send_download(command)
+        return DeleteDownloadResponse(command_id=command.command_id)

src/exo/shared/types/api.py

@@ -7,10 +7,11 @@ from pydantic import BaseModel, Field, field_validator
 from pydantic_core import PydanticUseDefault
 
 from exo.shared.models.model_cards import ModelCard, ModelId
-from exo.shared.types.common import CommandId
+from exo.shared.types.common import CommandId, NodeId
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.instances import Instance, InstanceId, InstanceMeta
-from exo.shared.types.worker.shards import Sharding
+from exo.shared.types.worker.shards import Sharding, ShardMetadata
+from exo.utils.pydantic_ext import CamelCaseModel
 
 FinishReason = Literal[
     "stop", "length", "tool_calls", "content_filter", "function_call", "error"
@@ -352,3 +353,16 @@ class ImageListItem(BaseModel, frozen=True):
 
 class ImageListResponse(BaseModel, frozen=True):
     data: list[ImageListItem]
+
+
+class StartDownloadParams(CamelCaseModel):
+    target_node_id: NodeId
+    shard_metadata: ShardMetadata
+
+
+class StartDownloadResponse(CamelCaseModel):
+    command_id: CommandId
+
+
+class DeleteDownloadResponse(CamelCaseModel):
+    command_id: CommandId