feat(slimrpc): add SlimRPC transport support to a2acli

[Tehsmash]

Summary

Adds SlimRPC as an opt-in transport in the `a2a` CLI, building on the transport/config redesign in #101.

Changes

`a2acli` SlimRPC integration

• New `slimrpc` Cargo feature on `a2acli`; gates `Binding::Slimrpc` variant in the CLI enum
• `--enabled-binding slimrpc` is accepted when the feature is enabled
• `SlimRpcTransportFactory` is registered with `A2AClientFactory` when `--enabled-binding slimrpc` is requested, so SLIMRPC transports are actually dispatched instead of falling through to JSONRPC

`a2a-slimrpc` config discovery and connection ID

• `SlimRpcTransportFactory::from_slim_config` and `SlimRpcTransport::from_slim_config` now call `create_app_from_slim_config_async` and propagate the returned `conn_id` via `new_with_connection`
• `slim.yaml` is discovered walking up from the current working directory (falling back to `~/.slim/config.yaml`), with environment variables taking highest priority

Transport binding observability

• `A2AClientFactory::create_from_card` now emits `info`-level tracing for candidate bindings, each attempt, and the selected binding

Depends on

PR #101 (`feat/cli-redesign-1929`) — this branch is stacked on top of it.

[gemini-code-assist]

Code Review

This pull request introduces configuration file support (.a2a.yaml) for the CLI, adds a new slimrpc transport feature, and refactors tenant handling by managing it within the client. Feedback on these changes highlights a compilation error due to a non-exhaustive match in Transport::protocol, a missing registration of SlimRpcTransportFactory in resolve_client, an absolute local path in Cargo.toml that will break external builds, and an opportunity to optimize request cloning in A2AClient when no tenant is specified.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

Adding the Slimrpc variant to Transport under #[cfg(feature = "slimrpc")] will cause a compilation error when the slimrpc feature is enabled, because the protocol method on Transport (defined right below) does not exhaustively match the new variant.

Please update Transport::protocol to handle the Slimrpc variant:

impl Transport {
    fn protocol(self) -> &'static str {
        match self {
            Transport::Jsonrpc => TRANSPORT_PROTOCOL_JSONRPC,
            Transport::HttpJson => TRANSPORT_PROTOCOL_HTTP_JSON,
            #[cfg(feature = "slimrpc")]
            Transport::Slimrpc => TRANSPORT_PROTOCOL_SLIMRPC,
        }
    }
}

[gemini-code-assist]

The a2a_slimrpc dependency is imported here, but the SlimRpcTransportFactory is never registered on the A2AClientFactory in resolve_client. Without registering the factory, the CLI will not be able to negotiate or use the slimrpc transport, even if --transport slimrpc is specified.

Please update resolve_client to register the factory when the slimrpc feature is enabled:

    let mut builder = A2AClientFactory::builder().preferred_bindings(preferred);

    #[cfg(feature = "slimrpc")]
    {
        let slimrpc_factory = a2a_slimrpc::SlimRpcTransportFactory::from_slim_config().await?;
        builder = builder.register(Arc::new(slimrpc_factory));
    }

[gemini-code-assist]

The dependency slim_bindings uses an absolute local path (/Users/sambetts/...). This will break builds on other environments and CI/CD pipelines. Please remove the local path or use a relative path if it is part of the same repository.

Suggested change

	slim_bindings = { package = "agntcy-slim-bindings", path = "/Users/sambetts/Work/src/github.com/agntcy/slim-bindings/rust", version = "2.0.0-alpha.2" }
	slim_bindings = { package = "agntcy-slim-bindings", version = "2.0.0-alpha.2" }

[gemini-code-assist]

To avoid unnecessary cloning and allocations (especially for requests with large payloads), only clone and patch the request when self.tenant is Some.

        let result = match &self.tenant {
            Some(tenant) => {
                let mut patched = req.clone();
                patched.tenant = Some(tenant.clone());
                self.transport.send_message(&params, &patched).await
            }
            None => self.transport.send_message(&params, req).await,
        };

[muscariello]

@Tehsmash we need a stable release for slimrpc. It's not a good idea to use this release. Please provide a stable release for slimrpc v2 first.
@micpapal @msardara can you please help with that ?