assistant2: Encourage diagnostics check (#27510)

Release Notes:

- N/A

crates/assistant2/src/thread.rs

@@ -873,17 +873,23 @@ impl Thread {
             request.messages.push(context_message);
         }
 
-        self.attach_stale_files(&mut request.messages, cx);
+        self.attached_tracked_files_state(&mut request.messages, cx);
 
         request
     }
 
-    fn attach_stale_files(&self, messages: &mut Vec<LanguageModelRequestMessage>, cx: &App) {
+    fn attached_tracked_files_state(
+        &self,
+        messages: &mut Vec<LanguageModelRequestMessage>,
+        cx: &App,
+    ) {
         const STALE_FILES_HEADER: &str = "These files changed since last read:";
 
         let mut stale_message = String::new();
 
-        for stale_file in self.action_log.read(cx).stale_buffers(cx) {
+        let action_log = self.action_log.read(cx);
+
+        for stale_file in action_log.stale_buffers(cx) {
             let Some(file) = stale_file.read(cx).file() else {
                 continue;
             };
@@ -895,10 +901,22 @@ impl Thread {
             writeln!(&mut stale_message, "- {}", file.path().display()).ok();
         }
 
+        let mut content = Vec::with_capacity(2);
+
         if !stale_message.is_empty() {
+            content.push(stale_message.into());
+        }
+
+        if action_log.has_edited_files_since_project_diagnostics_check() {
+            content.push(
+                "When you're done making changes, make sure to check project diagnostics and fix all errors AND warnings you introduced!".into(),
+            );
+        }
+
+        if !content.is_empty() {
             let context_message = LanguageModelRequestMessage {
                 role: Role::User,
-                content: vec![stale_message.into()],
+                content,
                 cache: false,
             };