Greentic MCP Tool Bridge

greentic-mcp provides the host-side tool registry and WASIX/WASI execution bridge used by flows to invoke MCP tools compiled to WebAssembly. It loads a declarative tool map, resolves tools by logical name, and executes them through Wasmtime with per-tool timeouts, retry hints, and transient error handling.

The crate leans on the shared contracts published in greentic-types and the WIT definitions plus generated bindings in greentic-interfaces. When a tool exposes the standard component ABI, the same bindings can be used to reach richer type-safe interfaces. Until those tools are widespread this crate ships a pointer/length fallback ABI that keeps local tool development unblocked.

Tool map configuration

Tool metadata is loaded from JSON or YAML. Each entry records where the tool artifact lives, the export to call, and optional execution hints.

tools:
  - name: echo
    component: ./tools/echo.wasm
    entry: tool_invoke
    timeout_ms: 1000
    max_retries: 2
    retry_backoff_ms: 200

Use greentic_mcp::load_tool_map to parse the file and build a ToolMap.

use greentic_mcp::{invoke_with_map, load_tool_map, WasixExecutor};
use serde_json::json;
use std::path::Path;

# #[tokio::main]
# async fn main() -> Result<(), Box<dyn std::error::Error>> {
let map = load_tool_map(Path::new("toolmap.yaml"))?;
let executor = WasixExecutor::new()?;

let echoed = invoke_with_map(&map, &executor, "echo", json!({"hello": "world"}))
    .await?;

assert_eq!(echoed, json!({"hello": "world"}));
# Ok(())
# }

WasixExecutor ensures that traps bubble up as transient errors, applies exponential backoff with jitter between retries, and converts wall-clock timeouts into McpError::Timeout.

ABI contracts

See ABI.md for details on the fallback pointer/length interface used by the integration tests. When a tool exports the canonical Greentic component API, use the bindings from greentic-interfaces to avoid manual pointer management and to return strongly-typed Outcome<T> values.