Remote session connections can fall back to long polling when a proxy buffers the stream

What

Remote sessions receive updates over a streaming connection (SSE, a single long-lived connection the server keeps sending data down). Some proxies hold back that data, so the connection looks silent. The CCR SSE connection used by remote sessions now has a fallback to long polling, where the client asks the server for a response, the server answers and closes, and the client immediately asks again.

• The connection counts, per connection, how many body bytes arrived and how many connections in a row closed without delivering anything (bodyBytesThisConnection, silentConnectionStreak).
• After a run of silent connections it switches into long-poll mode (longPollMode) and asks the server for long-poll responses on later connects (askedLongPollThisConnection). The message it records says it is "asking the server for long-poll responses (a proxy may be buffering the response body)".
• When a long-poll connection finishes cleanly and either moved the conversation forward or ran past a time limit, it logs SSETransport: Long poll completed, reopening and reopens at once instead of going through the normal reconnect path. Before, a stream ending always logged SSETransport: Stream ended, reconnecting.
• Redials in long-poll mode are quiet (quietRedial) and skip the usual connection reporting.
• The timeout that decides a connection is dead now allows for the long-poll interval the server reports back. Before, it was keepaliveIntervalMs() plus a fixed margin.
• The environment variable CLAUDE_CODE_CCR_LONG_POLL overrides the behaviour: true forces long polling, false turns it off.
• Without that variable, the new longPollFallback option decides. It is set only when the client owns the process, a further check passes, and the gate tengu_ccr_sse_long_poll_fallback allows it. Nothing has been read about that gate's value.

Why

If your network sits behind a proxy that buffers streamed responses, a remote session could appear to hang or keep reconnecting. This fallback gives such connections another way to get updates, and CLAUDE_CODE_CCR_LONG_POLL lets you force it on or off yourself.