agent: Improve initial file search quality (#29317)

This PR significantly improves the quality of the initial file search
that occurs when the model doesn't yet know the full path to a file it
needs to read/edit.

Previously, the assertions in file_search often failed on main as the
model attempted to guess full file paths. On this branch, it reliably
calls `find_path` (previously `path_search`) before reading files.

After getting the model to find paths first, I noticed it would try
using `grep` instead of `path_search`. This motivated renaming
`path_search` to `find_path` (continuing the analogy to unix commands)
and adding system prompt instructions about proper tool selection.

Note: I know the command is just called `find`, but that seemed too
general.

In my eval runs, the `file_search` example improved from 40% ± 10% to
98% ± 2%. The only assertion I'm seeing occasionally fail is "glob
starts with `**` or project". We can probably add some instructions in
that regard.

Release Notes:

- N/A

crates/eval/src/examples/file_search.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use assistant_tools::PathSearchToolInput;
+use assistant_tools::FindPathToolInput;
 use async_trait::async_trait;
 use regex::Regex;
 
@@ -15,7 +15,7 @@ impl Example for FileSearchExample {
             url: "https://github.com/zed-industries/zed.git".to_string(),
             revision: "03ecb88fe30794873f191ddb728f597935b3101c".to_string(),
             language_server: None,
-            max_assertions: Some(4),
+            max_assertions: Some(3),
         }
     }
 
@@ -32,21 +32,18 @@ impl Example for FileSearchExample {
         ));
 
         let response = cx.run_turn().await?;
-        let tool_use = response.expect_tool("path_search", cx)?;
-        let input = tool_use.parse_input::<PathSearchToolInput>()?;
+        let tool_use = response.expect_tool("find_path", cx)?;
+        let input = tool_use.parse_input::<FindPathToolInput>()?;
 
         let glob = input.glob;
-        cx.assert(
-            glob.ends_with(FILENAME),
-            format!("glob ends with `{FILENAME}`"),
-        )?;
+        cx.assert(glob.ends_with(FILENAME), "glob ends with file name")?;
 
         let without_filename = glob.replace(FILENAME, "");
         let matches = Regex::new("(\\*\\*|zed)/(\\*\\*?/)?")
             .unwrap()
             .is_match(&without_filename);
 
-        cx.assert(matches, "glob starts with either `**` or `zed`")?;
+        cx.assert(matches, "glob starts with `**` or project")?;
 
         Ok(())
     }