From 64a2e09122813cde90716c767a85d271c86701ea Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+universeplayer@users.noreply.github.com>
Date: Thu, 26 Mar 2026 18:39:07 +0800
Subject: [PATCH] fix: send SSE heartbeat to prevent WebChat disconnect during
 compression

When context compression triggers with slow reasoning models (e.g.
deepseek-reasoner), the backend can go 30+ seconds without pushing any
SSE data. The client-side EventSource / browser then assumes the
connection is dead and disconnects, causing the WebUI to hang
indefinitely since it never receives the eventual response.

Fix: yield an SSE comment (`: heartbeat`) on every empty poll cycle.
Comment lines are defined in the SSE spec as keep-alive signals --
the EventSource API ignores them but the HTTP connection stays open.

Fixes #6938
---
 astrbot/dashboard/routes/chat.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/astrbot/dashboard/routes/chat.py b/astrbot/dashboard/routes/chat.py
index c79ad1e355..97c006a1d0 100644
--- a/astrbot/dashboard/routes/chat.py
+++ b/astrbot/dashboard/routes/chat.py
@@ -40,6 +40,9 @@ async def _poll_webchat_stream_result(back_queue, username: str):
     try:
         result = await asyncio.wait_for(back_queue.get(), timeout=1)
     except asyncio.TimeoutError:
+        # Return a sentinel so the caller can send an SSE heartbeat to
+        # keep the connection alive during long-running operations (e.g.
+        # context compression with reasoning models).  See #6938.
         return None, False
     except asyncio.CancelledError:
         logger.debug(f"[WebChat] 用户 {username} 断开聊天长连接。")
@@ -364,6 +367,11 @@ async def stream():
                             client_disconnected = True
                             break
                         if not result:
+                            # Send an SSE comment as keep-alive so the client
+                            # doesn't time out during slow backend ops like
+                            # context compression with reasoning models (#6938).
+                            if not client_disconnected:
+                                yield ": heartbeat\n\n"
                             continue
 
                         if (