Messages are UTF-8 JSON-RPC, one per line. Standard output carries only protocol messages; diagnostics belong on standard error.
Both protocol eras share the stream. A legacy initialize is an admission barrier: its outcome is visible before later requests or
notifications on the connection are dispatched. Ordinary requests still run concurrently and replies may arrive out of order.
Era negotiation
Auto mode probes modern first. ContextClientOptions.ProbeTimeout defaults to 5 seconds; newly spawned processes get an additional
ProcessStartupAllowance of 10 seconds on their first probe (15 seconds total), still within the 30-second ConnectTimeout.
Silence or a recoverable transport failure can trigger legacy fallback for that connection, but cannot teach the cache that the server
is legacy. Only a definitive rejection or an explicit legacy-only version list can do that. Other protocol errors and malformed
probe responses also remain uncached.
The default in-memory EraCache expires a legacy choice five minutes after a definitive probe, even if cached legacy connections keep
succeeding. This lets a dual-era or upgraded server be probed again. Modern choices remain until forgotten or negotiation fails.
Construct EraCache with a clock and legacy lifetime to change expiration; custom IEraCache implementations own their expiration policy.
Backpressure
NewlineChannel queues at most 1 MiB of output, except that a single larger message is accepted into an empty queue. One additional
block may be in flight to the stream. Writers wait before copying when the queue has no room. The connection also stops reading
input while that queue is full, and awaits rejection writes, so a peer that never reads cannot create an unbounded backlog of replies.
Handler concurrency remains subject to ContextServerOptions.MaxConcurrentRequests (256 by default).
The cost of that bound: a single-threaded peer that writes more than about 1 MiB of requests before reading any response can block against the paused input, because the server stops reading until its replies are read. Clients should read and write concurrently, as the protocol already expects.
EOF and shutdown
Input EOF is a half-close: admitted handlers may finish and their queued replies are drained before output closes.
ContextServerOptions.EndOfStreamTimeout gives handlers a 5-second grace period, followed by cancellation and a bounded 5-second
shutdown wait. Total EOF linger, including output draining, is at most grace plus shutdown: 10 seconds by default.
The JSON-RPC layer exposes both bounds as JsonRpcConnectionOptions.EndOfStreamTimeout and ShutdownTimeout.
Output progress is checked after each 16 KiB write. A successful write resets the no-progress deadline (the shutdown timeout, 5 seconds by default); a reader that starts late or reads slowly is not cut off by a fixed one-second drain deadline. The total shutdown bound still applies. Transport failure or a reader that remains stalled past either deadline closes the output; a failed write is never followed by another message on that stream. Like any bounded transport shutdown, this cannot guarantee delivery to a peer that has stopped reading or disconnected halfway through a message.
Explicit cancellation and transport faults skip the handler grace period. Standalone NewlineChannel disposal uses the same
5-second idle and 10-second total output bounds with TimeProvider.System; connections inject their clock and configured bounds.