Webchat dissapearring messages
✅Solved
Webchat: Assistant messages disappear when next message streams in
Version: 2026.3.2, macOS, Chrome, local gateway
My assistant sends a long response (tables, multiple paragraphs with inline images). It renders fine. Then when I send a follow-up and the next response starts streaming, the previous message vanishes from the chat. Page refresh brings it back.
What I've tried:
Set blockStreamingDefault: "off" in agents.defaults — didn't fix it
Not related to heartbeats (no heartbeat running when it happens)
Happens with both long AND short previous messages
Filed as issue #33641
Repro: Send any message → get response → send follow-up → previous response disappears during streaming of new response
Anyone found a fix or workaround? Is this a known chat.history truncation issue or a UI rendering race condition?
Version: 2026.3.2, macOS, Chrome, local gateway
My assistant sends a long response (tables, multiple paragraphs with inline images). It renders fine. Then when I send a follow-up and the next response starts streaming, the previous message vanishes from the chat. Page refresh brings it back.
What I've tried:
Set blockStreamingDefault: "off" in agents.defaults — didn't fix it
Not related to heartbeats (no heartbeat running when it happens)
Happens with both long AND short previous messages
Filed as issue #33641
Repro: Send any message → get response → send follow-up → previous response disappears during streaming of new response
Anyone found a fix or workaround? Is this a known chat.history truncation issue or a UI rendering race condition?
Solution
Bug is FIXED! 
Massive thanks @Krill — your diagnosis was spot on and your patch suggestions were exactly what we needed.
Final working fix was two changes you outlined:
1. Always merge (
2. 500ms
Both were necessary — merge-only wasn't enough because
Tested with multiple long responses (10+ paragraphs, markdown tables, 4-6 tool calls each) followed by immediate follow-ups — messages stay visible. Full patch details posted on GitHub #33641.
Really appreciate you walking us through the architecture and giving us concrete code to work with. Couldn't have done it without you. This community is brilliant.
Massive thanks @Krill — your diagnosis was spot on and your patch suggestions were exactly what we needed.Final working fix was two changes you outlined:
1. Always merge (
mergeByStableKeystate.chatMessagesloadChatHistory()2. 500ms
setTimeoutchat finalloadChatHistoryapp-gateway.tsBoth were necessary — merge-only wasn't enough because
chatRunIdTested with multiple long responses (10+ paragraphs, markdown tables, 4-6 tool calls each) followed by immediate follow-ups — messages stay visible. Full patch details posted on GitHub #33641.
Really appreciate you walking us through the architecture and giving us concrete code to work with. Couldn't have done it without you. This community is brilliant.
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