Add thinking tool (#26675)

Release Notes:

- N/A

crates/assistant_tools/src/thinking_tool.rs

@@ -0,0 +1,47 @@
+use std::sync::Arc;
+
+use anyhow::{anyhow, Result};
+use assistant_tool::Tool;
+use gpui::{App, Entity, Task};
+use language_model::LanguageModelRequestMessage;
+use project::Project;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Serialize, Deserialize, JsonSchema)]
+pub struct ThinkingToolInput {
+    /// Content to think about. This should be a description of what to think about or
+    /// a problem to solve.
+    content: String,
+}
+
+pub struct ThinkingTool;
+
+impl Tool for ThinkingTool {
+    fn name(&self) -> String {
+        "thinking".to_string()
+    }
+
+    fn description(&self) -> String {
+        include_str!("./thinking_tool/description.md").to_string()
+    }
+
+    fn input_schema(&self) -> serde_json::Value {
+        let schema = schemars::schema_for!(ThinkingToolInput);
+        serde_json::to_value(&schema).unwrap()
+    }
+
+    fn run(
+        self: Arc<Self>,
+        input: serde_json::Value,
+        _messages: &[LanguageModelRequestMessage],
+        _project: Entity<Project>,
+        _cx: &mut App,
+    ) -> Task<Result<String>> {
+        // This tool just "thinks out loud" and doesn't perform any actions.
+        Task::ready(match serde_json::from_value::<ThinkingToolInput>(input) {
+            Ok(_input) => Ok("Finished thinking.".to_string()),
+            Err(err) => Err(anyhow!(err)),
+        })
+    }
+}