The /planning/:sessionId/stream route only replayed buffered events when
the client sent a Last-Event-ID (resume case). On a fresh subscription it
just attached as a live subscriber. On slower devices (mobile especially),
the agent often streamed several thinking deltas into the buffer before
the SSE connection finished establishing — so the user saw the spinner
sit there, then a question appear out of nowhere, with no streaming
"thinking" content.
When a session has no current question or summary yet (i.e. the agent is
generating its first response) and the client connects without a
Last-Event-ID, replay every buffered event before attaching the live
subscription. This catches up the user on the in-flight thinking stream.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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