fix(server): graceful stream termination on cancellation (issue #847) (#850)

* fix(server): graceful stream termination on cancellation (issue #847)

* Update the code with review suggestion

web/src/core/api/chat.ts

@@ -84,6 +84,7 @@ export async function* chatStream(
     });
     
     for await (const event of stream) {
+      if (event.data == null) continue;
       yield {
         type: event.event,
         data: JSON.parse(event.data),

web/src/core/api/types.ts

@@ -84,10 +84,20 @@ export interface CitationsEvent {
   };
 }
 
+export interface ErrorEvent {
+  type: "error";
+  data: {
+    thread_id: string;
+    error: string;
+    reason?: "cancelled" | string;
+  };
+}
+
 export type ChatEvent =
   | MessageChunkEvent
   | ToolCallsEvent
   | ToolCallChunksEvent
   | ToolCallResultEvent
   | InterruptEvent
-  | CitationsEvent;
+  | CitationsEvent
+  | ErrorEvent;

web/src/core/messages/merge-message.ts

@@ -53,7 +53,7 @@ export function mergeMessage(message: Message, event: ChatEvent) {
   } else if (event.type === "interrupt") {
     mergeInterruptMessage(message, event);
   }
-  if (event.type !== "citations" && event.data.finish_reason) {
+  if (event.type !== "citations" && event.type !== "error" && event.data.finish_reason) {
     message.finishReason = event.data.finish_reason;
     message.isStreaming = false;
     if (message.toolCalls) {

web/src/core/store/store.ts

@@ -155,7 +155,14 @@ export async function sendMessage(
     for await (const event of stream) {
       const { type, data } = event;
       let message: Message | undefined;
-      
+
+      if (type === "error") {
+        // Server sent an error event - check if it's user cancellation
+        if (data.reason !== "cancelled") {
+          toast(data.error || "An error occurred while generating the response.");
+        }
+        break;
+      }
       // Handle citations event: store citations for the current research
       if (type === "citations") {
         const ongoingResearchId = useStore.getState().ongoingResearchId;
@@ -207,10 +214,12 @@ export async function sendMessage(
         scheduleUpdate();
       }
     }
-  } catch {
-    toast("An error occurred while generating the response. Please try again.");
+  } catch (error) {
+    const isAborted = (error as Error).name === "AbortError";
+    if (!isAborted) {
+      toast("An error occurred while generating the response. Please try again.");
+    }
     // Update message status.
-    // TODO: const isAborted = (error as Error).name === "AbortError";
     if (messageId != null) {
       const message = getMessage(messageId);
       if (message?.isStreaming) {