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;