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Add HttpServerSessionMode for hybrid stateful/stateless HTTP serving (#1796)

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Jeff Handley <jeffhandley@users.noreply.github.com>
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pardhu 2026-08-12 23:36:36 -07:00 • committed by GitHub
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docs/concepts/roots/roots.md
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@ -112,7 +112,7 @@ server.RegisterNotificationHandler(
[MRTR](xref:mrtr) is the SEP-2322 mechanism for server-driven input requests, finalized in protocol revision `2026-07-28`. In that revision, the server-to-client `roots/list` request method is removed; the recommended way to ask the client for its roots from a server handler is to throw <xref:ModelContextProtocol.Protocol.InputRequiredException> and let the SDK emit an <xref:ModelContextProtocol.Protocol.InputRequiredResult> on the wire.
> [!IMPORTANT]
> `RequestRootsAsync` throws `InvalidOperationException("Roots are not supported in stateless mode.")` whenever the server is running stateless — including Streamable HTTP requests served under `2026-07-28` with `Stateless = true`. Stdio servers and initialize-handshake stateful Streamable HTTP sessions continue to work via the initialize-era server-to-client `roots/list` request flow; an HTTP server set to `Stateless = false` refuses `2026-07-28` so dual-path clients can fall back before using that flow. For code that needs to run on stateless servers — including `2026-07-28` Streamable HTTP — throw `InputRequiredException` from your handler instead. It works under both protocols and both session modes.
> `RequestRootsAsync` throws `InvalidOperationException("Roots are not supported in stateless mode.")` whenever the server is running stateless — including every Streamable HTTP request served under `2026-07-28`. Stdio servers and initialize-handshake stateful Streamable HTTP sessions continue to work via the initialize-era server-to-client `roots/list` request flow; an HTTP server set to `SessionMode = HttpServerSessionMode.Stateful` refuses `2026-07-28` so dual-path clients can fall back before using that flow, while `HttpServerSessionMode.StatefulForInitializeClients` instead serves `2026-07-28` statelessly on the same endpoint (see [hybrid mode](xref:stateless#hybrid-mode-sessions-for-initialize-clients-only)), so those requests use MRTR while `initialize`-handshake sessions keep this flow. For code that needs to run on stateless servers — including `2026-07-28` Streamable HTTP — throw `InputRequiredException` from your handler instead. It works across both protocol eras and all three HTTP `SessionMode` configurations.
For example: