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/assistant_tools/src/assistant_tools.rs

@@ -9,12 +9,12 @@ mod delete_path_tool;
 mod diagnostics_tool;
 mod edit_file_tool;
 mod fetch_tool;
+mod find_path_tool;
 mod grep_tool;
 mod list_directory_tool;
 mod move_path_tool;
 mod now_tool;
 mod open_tool;
-mod path_search_tool;
 mod read_file_tool;
 mod rename_tool;
 mod replace;
@@ -45,11 +45,11 @@ use crate::delete_path_tool::DeletePathTool;
 use crate::diagnostics_tool::DiagnosticsTool;
 use crate::edit_file_tool::EditFileTool;
 use crate::fetch_tool::FetchTool;
+use crate::find_path_tool::FindPathTool;
 use crate::grep_tool::GrepTool;
 use crate::list_directory_tool::ListDirectoryTool;
 use crate::now_tool::NowTool;
 use crate::open_tool::OpenTool;
-use crate::path_search_tool::PathSearchTool;
 use crate::read_file_tool::ReadFileTool;
 use crate::rename_tool::RenameTool;
 use crate::symbol_info_tool::SymbolInfoTool;
@@ -58,7 +58,7 @@ use crate::thinking_tool::ThinkingTool;
 
 pub use create_file_tool::CreateFileToolInput;
 pub use edit_file_tool::EditFileToolInput;
-pub use path_search_tool::PathSearchToolInput;
+pub use find_path_tool::FindPathToolInput;
 pub use read_file_tool::ReadFileToolInput;
 
 pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
@@ -81,7 +81,7 @@ pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
     registry.register_tool(OpenTool);
     registry.register_tool(CodeSymbolsTool);
     registry.register_tool(ContentsTool);
-    registry.register_tool(PathSearchTool);
+    registry.register_tool(FindPathTool);
     registry.register_tool(ReadFileTool);
     registry.register_tool(GrepTool);
     registry.register_tool(RenameTool);