Ensure connection is closed for single-value SSE streams

[jsxs0]

Summary

Add ensure connection.close to SSE::Application#send_data so the Iodine connection is always closed for single-value SSE streams, even when Rage::SSE.__serialize or connection.write raises.

Problem

start_formatted_stream (Enumerator path) has ensure connection.close. start_raw_stream (Proc path) has a rescue block (#248). But send_data (single-value path) has no error handling — if __serialize raises (e.g. to_json on an object with circular references, encoding errors, or a broken to_json implementation), connection.close never executes and the connection leaks until Iodine's socket timeout.

# Before — connection.close only runs if serialize + write succeed
def send_data(connection)
  Rage::Telemetry.tracer.span_sse_stream_process(connection:, type: @type) do
    connection.write(Rage::SSE.__serialize(@stream))
    connection.close
  end
end

# After — connection always closes, matching start_formatted_stream pattern
def send_data(connection)
  Rage::Telemetry.tracer.span_sse_stream_process(connection:, type: @type) do
    connection.write(Rage::SSE.__serialize(@stream))
  end
ensure
  connection.close
end

Why ensure (not rescue)?

Single-value streams are synchronous and one-shot — the connection should always close after send_data, regardless of success or failure. This matches the ensure connection.close pattern already used by start_formatted_stream.

Test plan

Added 3 test cases for #send_data (single-value streams had no dedicated tests):

• Single value → writes serialized data and closes connection
• Serialization raises → connection still closed
• Write raises → connection still closed

bundle exec rspec spec/sse/ — 53 examples, 0 failures

[rsamoilov]

Looks good. Thank you 🚀

I'm extremely happy you're looking into the SSE functionality given your experience!