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fix(chat): release useAgentChat streaming protection when the socket closes - #2496
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useAgentChat protects a locally streaming assistant from behind snapshots until that request's done/error frame. A WebSocket close ends the local stream without that frame, so the protection stayed armed and swapped the cut-off local copy into every later cf_agent_chat_messages snapshot. The stored reply never showed, and the next send shipped the partial copy. Release the protection on close. A resumed replay re-arms it from its start chunk, so mid-stream resume still neither doubles nor drops text. Refs #2464
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Brings react-agui.tsx level with the legacy hook in agents/chat/react, which received these through the upstream merge: - cloudflare#2344 the server snapshot heals a diverged observed assistant - cloudflare#2348 an observer skips replayed continuation frames it already applied - cloudflare#2361 onToolCall fires only after the stream ends - cloudflare#2378 onTurnEnd fires once per ended request - cloudflare#2383 turns settle across replay, resume and observers (held and recovering requests, the resume:false idle probe) - cloudflare#2496 streaming protection is released when the socket closes - cloudflare#2394 follow the socket when the agent name changes - cloudflare#2403 the tool-result cleanup no longer dispatches per chunk - cloudflare#2039 keep an optimistic send the reconnect transcript omits The last three had no failing test: their upstream tests are ported into react-tests (the address-change one against a fake of useAgent's pending socket, since this package has no test worker) and failed before the fix. restoreBufferedSends, MAX_REMEMBERED_ENDED_TURNS and isSocketAddressPending are exported from agents/chat/react so the two hooks share them.
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Part of #2464, the client side. This fully fixes the bug for Think. AIChatAgent still needs its server-side change; see Merge Danger.
Summary
useAgentChatprotects a locally streaming assistant reply so that stale snapshots can't replace it. Only that request's done/error frame released the protection. When the socket closes mid-stream, the transport ends the local stream and that frame never arrives. The protection stayed armed, so every latercf_agent_chat_messagessnapshot had the cut-off local copy swapped back in. That included the full reply Think sends when a client reconnects between turns. The next send then shipped the cut-off copy to the server.onAgentClose() sawClose = true serverReportsRecovery = false fallbackAckedResumeRequestIds.clear() + protectedStreamingAssistantRef.current = null # the done/error frame won't comeIf the turn is still running on reconnect, the server's replayed
startchunk re-arms protection. The existing replay reset de-duplicates the text, and it doesn't depend on protection.Alternatives I rejected:
resume_noneidle: too late. Think's idle snapshot arrives before the probe answer, so the snapshot has already been overwritten, and this missesresume: false.Evidence
New tests in
packages/ai-chat/src/react-tests/use-agent-chat.test.tsx, in the describe block "useAgentChat stale reply after a mid-stream close (#2464)":HelHelThe three rows that pass on main guard against the fix breaking resume. Suites: ai-chat react 106/106, agents react 168/168, agents chat unit 615/615, Think react 2/2.
pnpm run checkpasses.Merge Danger
Door: two-way
The change is one line.
Blast Radius: chat clients
Every
useAgentChatuser, on both Think and AIChatAgent. The only path that changes is a socket close during a local stream; resume replays still re-arm protection.Still open in #2464:
Already on main, not changed here: sending a second message mid-stream, then a close and a resume, duplicates the first reply.