Manual no tool calls (#29745)

Now instead of the model hallucinating tool calls, we get requests for
more context:

<img width="620" alt="Screenshot 2025-05-01 at 12 45 49 PM"
src="https://github.com/user-attachments/assets/847d5c14-82f6-4234-b85a-8cd2bc7ab11d"
/>

It still knows how to answer general questions:
<img width="624" alt="Screenshot 2025-05-01 at 12 47 44 PM"
src="https://github.com/user-attachments/assets/43ab0fc3-4cc8-452f-b26b-474b5d31919f"
/>

Release Notes:

- Fixed the model still trying to do tool calls when no tools selected
(e.g. in `Manual` profile).

---------

Co-authored-by: Ben <ben@zed.dev>
Co-authored-by: Michael <michael@zed.dev>

crates/agent/src/context.rs

@@ -843,7 +843,7 @@ pub fn load_context(
         text.push_str(
             "\n<context>\n\
             The following items were attached by the user. \
-            You don't need to use other tools to read them.\n\n",
+            They are up-to-date and don't need to be re-read.\n\n",
         );
 
         if !file_context.is_empty() {

crates/agent/src/thread.rs

@@ -2509,7 +2509,7 @@ mod tests {
         let expected_context = format!(
             r#"
 <context>
-The following items were attached by the user. You don't need to use other tools to read them.
+The following items were attached by the user. They are up-to-date and don't need to be re-read.
 
 <files>
 ```rs {path_part}