feat(cli): redesign a2a CLI — transport flag, .a2a.yaml config, tenant injection

[Tehsmash]

Summary

Redesigns the a2a CLI and the a2a-client library per the proposal in issue #1929.

Changes

--transport flag (replaces --binding)

• --transport is now a repeatable, ordered flag (e.g. --transport jsonrpc --transport http-json)
• Default when omitted: [jsonrpc, http-json]
• SlimRPC must be explicitly listed even when compiled in with the slimrpc feature
• Removes the old --binding single-value flag

.a2a.yaml config file

• New hierarchical config file: walks from CWD up to (inclusive) the home directory looking for .a2a.yaml
• Supports: transports, bearer_token, headers, output
• CLI flags always take precedence; headers are additive (config first, then flags)
• Config discovery logic is in a2acli/src/config.rs with unit tests using tempfile

Tenant auto-injection from AgentInterface

• Removed --tenant CLI flag and any tenant field from the config file
• A2AClient now stores tenant: Option<String> (set via .with_tenant() builder)
• All 11 request-forwarding methods unconditionally override the request's tenant field with the client's stored value — callers cannot set tenant per-request
• A2AClientFactory::create_from_card chains .with_tenant(iface.tenant.clone()) so the tenant from the selected AgentInterface is automatically applied to every request

Output format

• --output / -o is now Option<OutputFormat> (no clap default); config file fills it in if absent; final fallback is pretty
• Enables the config file to control output format without conflicting with clap's default

Files changed

File	Change
a2acli/src/lib.rs	CLI struct, command parsing, request builders, output logic
a2acli/src/config.rs	New: config file discovery, loading, and merging
a2acli/Cargo.toml	Add serde_yaml, tempfile dev-dep
Cargo.toml	Add serde_yaml = "0.9" to workspace deps
a2a-client/src/client.rs	tenant field, with_tenant(), patching in all 11 methods
a2a-client/src/factory.rs	Chain .with_tenant(iface.tenant.clone())
a2acli/tests/e2e.rs	Update tests: --transport, remove --tenant, add config-file output test

[gemini-code-assist]

Code Review

This pull request refactors the A2A CLI binary to 'a2a', restructures subcommands (such as grouping task operations under a 'task' subcommand and renaming 'card' to 'discover'), adds support for reading agent cards from local files, and introduces a '.a2a.yaml' configuration file to load default CLI options. Feedback on these changes highlights several issues: a missing 'Slimrpc' variant in the 'Transport' enum causes compilation failures when the 'slimrpc' feature is enabled; the configuration search fails to find the home directory config when run from an unrelated directory tree; cloning requests on every client call is inefficient; and using synchronous file I/O inside an async function blocks the executor thread.

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[gemini-code-assist]

The Transport enum is missing the Slimrpc variant, which causes a compilation error in a2acli/src/config.rs when the slimrpc feature is enabled. Add the Slimrpc variant under the #[cfg(feature = "slimrpc")] attribute to match its usage in the configuration parsing logic.

Suggested change

	#[derive(Debug, Clone, Copy, PartialEq, Eq, ValueEnum)]
	pub enum Binding {
	pub enum Transport {
	Jsonrpc,
	HttpJson,
	}
	impl Binding {
	impl Transport {
	fn protocol(self) -> &'static str {
	match self {
	Binding::Jsonrpc => TRANSPORT_PROTOCOL_JSONRPC,
	Binding::HttpJson => TRANSPORT_PROTOCOL_HTTP_JSON,
	Transport::Jsonrpc => TRANSPORT_PROTOCOL_JSONRPC,
	Transport::HttpJson => TRANSPORT_PROTOCOL_HTTP_JSON,
	}
	}
	}
	#[derive(Debug, Clone, Copy, PartialEq, Eq, ValueEnum)]
	pub enum Transport {
	Jsonrpc,
	HttpJson,
	#[cfg(feature = "slimrpc")]
	Slimrpc,
	}
	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 => "slimrpc",
	}
	}
	}

[gemini-code-assist]

Cloning the entire SendMessageRequest on every client call can be highly inefficient, especially for large message payloads. Since most requests do not require overriding the tenant (or the tenant already matches), we can avoid cloning entirely by checking if self.tenant == req.tenant before cloning. This optimization can also be applied to the other request-forwarding methods in this file.

        let result = if self.tenant == req.tenant {
            self.transport.send_message(&params, req).await
        } else {
            let patched = SendMessageRequest {
                tenant: self.tenant.clone(),
                ..req.clone()
            };
            self.transport.send_message(&params, &patched).await
        };

[gemini-code-assist]

When the CLI is run from a directory outside the home directory tree (e.g., /tmp or another drive), walking up the directory tree will never reach the home directory. As a result, the global configuration file at ~/.a2a.yaml is completely ignored. Fall back to checking the home directory directly if the hierarchical search from the current working directory yields no config file.

pub fn find_config_file() -> Option<PathBuf> {
    let cwd = std::env::current_dir().ok()?;
    let home = home_dir();
    find_config_file_from(&cwd, home.as_deref()).or_else(|| {
        home.as_ref()
            .map(|h| h.join(CONFIG_FILENAME))
            .filter(|p| p.is_file())
    })
}

[gemini-code-assist]

Using std::fs::read_to_string inside an async fn blocks the async executor thread, which can degrade performance. Since tokio is already a dependency with the full feature set, use tokio::fs::read_to_string instead to perform non-blocking asynchronous file I/O.

Suggested change

	} else {
	let json = std::fs::read_to_string(agent_ref)?;
	serde_json::from_str(&json).map_err(|e| CliError::InvalidAgentCard {
	reason: e.to_string(),
	})
	}
	} else {
	let json = tokio::fs::read_to_string(agent_ref).await?;
	serde_json::from_str(&json).map_err(|e| CliError::InvalidAgentCard {
	reason: e.to_string(),
	})
	}

[msardara]

LGTM ✅