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//! MCP bridge seam for the agentic loop.
//!
//! The loop advertises and dispatches remote MCP tools (namespaced
//! `server__tool`) alongside the built-ins. The concrete connection pool
//! (`Mcp` in `newt-tui`) wraps `newt-mcp-client`, which itself depends on
//! `newt-core` — so the loop cannot name that type without a dependency
//! cycle. This minimal trait is the seam: `newt-tui` implements it for its
//! `Mcp` pool with three one-line forwarders.
//!
//! NOTE: this is deliberately NOT an inference-backend abstraction.
//! `ChatCtx` stays a concrete type per the Step 9.7 spec (no
//! `InferenceBackend` trait until a second implementor exists).
/// Bridge to connected MCP servers used by the agentic loop.
#[async_trait::async_trait]
pub trait McpTools: Send {
/// Whether this bridge routes `name` (an MCP-namespaced `server__tool`).
fn handles(&self, name: &str) -> bool;
/// Tool definitions advertised to the model in addition to the built-ins.
fn tool_defs(&self) -> Vec<serde_json::Value>;
/// Invoke the remote tool and return the result text fed back to the model.
async fn call(&mut self, name: &str, args: &serde_json::Value) -> String;
}
/// The no-servers bridge: handles nothing, advertises nothing. Used by
/// headless callers without MCP config and by the loop's unit tests
/// (mirrors the old `Mcp::empty()` behavior exactly).
pub struct NoMcp;
#[async_trait::async_trait]
impl McpTools for NoMcp {
fn handles(&self, _name: &str) -> bool {
false
}
fn tool_defs(&self) -> Vec<serde_json::Value> {
Vec::new()
}
async fn call(&mut self, _name: &str, _args: &serde_json::Value) -> String {
// Unreachable through the loop (it only calls after `handles()`),
// but fail soft for any direct caller.
"error: no MCP servers connected".to_string()
}
}