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/migrator/src/migrations.rs

@@ -51,3 +51,9 @@ pub(crate) mod m_2025_04_21 {
 
     pub(crate) use settings::SETTINGS_PATTERNS;
 }
+
+pub(crate) mod m_2025_04_23 {
+    mod settings;
+
+    pub(crate) use settings::SETTINGS_PATTERNS;
+}

crates/migrator/src/migrations/m_2025_04_23/settings.rs

@@ -0,0 +1,27 @@
+use std::ops::Range;
+use tree_sitter::{Query, QueryMatch};
+
+use crate::MigrationPatterns;
+use crate::patterns::SETTINGS_ASSISTANT_TOOLS_PATTERN;
+
+pub const SETTINGS_PATTERNS: MigrationPatterns =
+    &[(SETTINGS_ASSISTANT_TOOLS_PATTERN, rename_path_search_tool)];
+
+fn rename_path_search_tool(
+    contents: &str,
+    mat: &QueryMatch,
+    query: &Query,
+) -> Option<(Range<usize>, String)> {
+    let tool_name_capture_ix = query.capture_index_for_name("tool_name")?;
+    let tool_name_range = mat
+        .nodes_for_capture_index(tool_name_capture_ix)
+        .next()?
+        .byte_range();
+    let tool_name = contents.get(tool_name_range.clone())?;
+
+    if tool_name == "path_search" {
+        return Some((tool_name_range, "find_path".to_string()));
+    }
+
+    None
+}

crates/migrator/src/migrator.rs

@@ -132,6 +132,10 @@ pub fn migrate_settings(text: &str) -> Result<Option<String>> {
             migrations::m_2025_04_21::SETTINGS_PATTERNS,
             &SETTINGS_QUERY_2025_04_21,
         ),
+        (
+            migrations::m_2025_04_23::SETTINGS_PATTERNS,
+            &SETTINGS_QUERY_2025_04_23,
+        ),
     ];
     run_migrations(text, migrations)
 }
@@ -214,6 +218,10 @@ define_query!(
     SETTINGS_QUERY_2025_04_21,
     migrations::m_2025_04_21::SETTINGS_PATTERNS
 );
+define_query!(
+    SETTINGS_QUERY_2025_04_23,
+    migrations::m_2025_04_23::SETTINGS_PATTERNS
+);
 
 // custom query
 static EDIT_PREDICTION_SETTINGS_MIGRATION_QUERY: LazyLock<Query> = LazyLock::new(|| {
@@ -639,7 +647,7 @@ mod tests {
                                 "name": "Custom",
                                 "tools": {
                                     "diagnostics": true,
-                                    "path_search": true,
+                                    "find_path": true,
                                     "read_file": true
                                 }
                             }
@@ -650,4 +658,40 @@ mod tests {
             None,
         )
     }
+
+    #[test]
+    fn test_rename_path_search_to_find_path() {
+        assert_migrate_settings(
+            r#"
+                {
+                    "assistant": {
+                        "profiles": {
+                            "default": {
+                                "tools": {
+                                    "path_search": true,
+                                    "read_file": true
+                                }
+                            }
+                        }
+                    }
+                }
+            "#,
+            Some(
+                r#"
+                {
+                    "assistant": {
+                        "profiles": {
+                            "default": {
+                                "tools": {
+                                    "find_path": true,
+                                    "read_file": true
+                                }
+                            }
+                        }
+                    }
+                }
+            "#,
+            ),
+        );
+    }
 }