add purpose field to tool specs

Author: brandonskiser

crates/agent/src/agent/agent_config/parse.rs

@@ -6,7 +6,7 @@ use std::str::FromStr;
 use crate::agent::agent_loop::types::ToolUseBlock;
 use crate::agent::protocol::AgentError;
 use crate::agent::tools::BuiltInToolName;
-use crate::agent::util::path::canonicalize_path_impl;
+use crate::agent::util::path::canonicalize_path_sys;
 use crate::agent::util::providers::{
     RealProvider,
     SystemProvider,
@@ -32,7 +32,7 @@ impl<'a> ResourceKind<'a> {
 
         let file_path = value.trim_start_matches("file://");
         if file_path.contains('*') || file_path.contains('?') {
-            let canon = canonicalize_path_impl(file_path, sys, sys, sys)
+            let canon = canonicalize_path_sys(file_path, sys)
                 .map_err(|err| format!("Failed to canonicalize path for {}: {}", file_path, err))?;
             let pattern = glob::Pattern::new(canon.as_str())
                 .map_err(|err| format!("Failed to create glob for {}: {}", canon, err))?;
@@ -258,7 +258,7 @@ impl FromStr for CanonicalToolName {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::agent::util::test::TestSystem;
+    use crate::agent::util::test::TestProvider;
 
     #[test]
     fn test_resource_kind_parse_nonfile() {
@@ -270,7 +270,7 @@ mod tests {
 
     #[test]
     fn test_resource_kind_parse_file_scheme() {
-        let sys = TestSystem::new();
+        let sys = TestProvider::new();
 
         let resource = "file://project/README.md";
         assert_eq!(ResourceKind::parse_impl(resource, &sys).unwrap(), ResourceKind::File {

crates/agent/src/agent/consts.rs

@@ -15,3 +15,6 @@ pub const MAX_TOOL_SPEC_DESCRIPTION_LEN: usize = 10_004;
 
 /// 10 MB
 pub const MAX_IMAGE_SIZE_BYTES: u64 = 10 * 1024 * 1024;
+
+pub const TOOL_USE_PURPOSE_FIELD_NAME: &str = "__tool_use_purpose";
+pub const TOOL_USE_PURPOSE_FIELD_DESCRIPTION: &str = "A brief explanation why you are making this tool use.";

crates/agent/src/agent/mcp/service.rs

@@ -45,6 +45,7 @@ use crate::agent::agent_config::definitions::McpServerConfig;
 use crate::agent::agent_loop::types::ToolSpec;
 use crate::agent::util::expand_env_vars;
 use crate::agent::util::path::expand_path;
+use crate::util::providers::RealProvider;
 
 /// This struct is consumed by the [rmcp] crate on server launch. The only purpose of this struct
 /// is to handle server-to-client requests. Client-side code will own a [RunningMcpService]
@@ -71,7 +72,9 @@ impl McpService {
     pub async fn launch(self) -> eyre::Result<(RunningMcpService, LaunchMetadata)> {
         match &self.config {
             McpServerConfig::Local(config) => {
-                let cmd = expand_path(&config.command)?;
+                // TODO - don't use real provider
+                let cmd = expand_path(&config.command, &RealProvider)?;
+
                 let mut env_vars = config.env.clone();
                 let cmd = Command::new(cmd.as_ref() as &str).configure(|cmd| {
                     if let Some(envs) = &mut env_vars {