Streaming tool calls (#29179)

https://github.com/user-attachments/assets/7854a737-ef83-414c-b397-45122e4f32e8



Release Notes:

- Create file and edit file tools now stream their tool descriptions, so
you can see what they're doing sooner.

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/agent/src/thread.rs

@@ -1293,12 +1293,27 @@ impl Thread {
                                         thread.insert_message(Role::Assistant, vec![], cx)
                                     });
 
-                                thread.tool_use.request_tool_use(
+                                let tool_use_id = tool_use.id.clone();
+                                let streamed_input = if tool_use.is_input_complete {
+                                    None
+                                } else {
+                                    Some((&tool_use.input).clone())
+                                };
+
+                                let ui_text = thread.tool_use.request_tool_use(
                                     last_assistant_message_id,
                                     tool_use,
                                     tool_use_metadata.clone(),
                                     cx,
                                 );
+
+                                if let Some(input) = streamed_input {
+                                    cx.emit(ThreadEvent::StreamedToolUse {
+                                        tool_use_id,
+                                        ui_text,
+                                        input,
+                                    });
+                                }
                             }
                         }
 
@@ -2189,6 +2204,11 @@ pub enum ThreadEvent {
     StreamedCompletion,
     StreamedAssistantText(MessageId, String),
     StreamedAssistantThinking(MessageId, String),
+    StreamedToolUse {
+        tool_use_id: LanguageModelToolUseId,
+        ui_text: Arc<str>,
+        input: serde_json::Value,
+    },
     Stopped(Result<StopReason, Arc<anyhow::Error>>),
     MessageAdded(MessageId),
     MessageEdited(MessageId),