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feat: add modern client lifecycle modes (SEP-2575) (#995)

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* feat: add modern client lifecycle modes

* refactor: drop modern naming and dead cleanup

* fix: gate request metadata on inline lifecycle only
This commit is contained in:
Dale Seo 2026-07-16 17:12:16 -04:00 • committed by GitHub
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43
README.md
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@ -74,6 +74,44 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
```
</details>
### Client lifecycle modes
`serve()` uses the legacy MCP lifecycle: the client sends `initialize`, receives
the negotiated server information, and then sends `notifications/initialized`.
Use [`ClientServiceExt::serve_with_lifecycle`](crates/rmcp/src/service/client.rs) to
select another lifecycle explicitly:
```rust, ignore
use rmcp::{ClientInfo, ClientLifecycleMode, ClientServiceExt, ProtocolVersion};
// Start directly with server/discover and include client metadata on every request.
let client = ClientInfo::default()
.serve_with_lifecycle(
transport,
ClientLifecycleMode::Discover {
preferred_versions: vec![ProtocolVersion::V_2026_07_28],
},
)
.await?;
// Or probe the discover lifecycle and fall back when a legacy server reports
// that server/discover is not implemented.
let client = ClientInfo::default()
.serve_with_lifecycle(
transport,
ClientLifecycleMode::Auto {
preferred_versions: vec![ProtocolVersion::V_2026_07_28],
legacy_version: Some(ProtocolVersion::V_2025_11_25),
},
)
.await?;
```
`ClientLifecycleMode::Initialize` is equivalent to the existing `serve()` behavior.
Discover startup does not send `notifications/initialized`; discovery completes
startup, and each subsequent request carries its protocol version, client
information, and capabilities in `_meta`.
### Build a Server
<details>
@ -812,10 +850,11 @@ impl ServerHandler for MyServer {
### Initialized notification
Clients send `initialized` after the handshake completes:
Legacy clients send `initialized` after the `initialize` handshake completes.
Clients using `ClientLifecycleMode::Discover` do not send this notification:
```rust
// Sent automatically by rmcp during the serve() handshake.
// Sent automatically by rmcp during the legacy serve() handshake.
// Servers handle it via:
impl ServerHandler for MyServer {
async fn on_initialized(