Settle HTTP responses before reconnecting after cutoff

[kentbull]

Summary

• settle the old response generation before reopening after connector cutoff
• preserve valid close-delimited responses and expose truncated framed responses as errors
• parse accepted SSE events before applying their reconnect interval
• clear residual old-generation bytes after settlement and defer new connection work

Why

EOF belongs to the transport generation that observed it. Reopening first resets the response parser before it can classify the old bytes, collapsing three different outcomes: a valid close-delimited response, a truncated framed response, and an SSE stream whose final accepted event changes reconnect timing. Settling the old parser before reconnect preserves message framing, failure truth, and application-visible SSE state.