Lay the groundwork to support history in agent2 (#36483)

This pull request introduces title generation and history replaying. We
still need to wire up the rest of the history but this gets us very
close. I extracted a lot of this code from `agent2-history` because that
branch was starting to get long-lived and there were lots of changes
since we started.

Release Notes:

- N/A

crates/acp_thread/src/acp_thread.rs

@@ -537,9 +537,15 @@ impl ToolCallContent {
             acp::ToolCallContent::Content { content } => {
                 Self::ContentBlock(ContentBlock::new(content, &language_registry, cx))
             }
-            acp::ToolCallContent::Diff { diff } => {
-                Self::Diff(cx.new(|cx| Diff::from_acp(diff, language_registry, cx)))
-            }
+            acp::ToolCallContent::Diff { diff } => Self::Diff(cx.new(|cx| {
+                Diff::finalized(
+                    diff.path,
+                    diff.old_text,
+                    diff.new_text,
+                    language_registry,
+                    cx,
+                )
+            })),
         }
     }
 
@@ -682,6 +688,7 @@ pub struct AcpThread {
 #[derive(Debug)]
 pub enum AcpThreadEvent {
     NewEntry,
+    TitleUpdated,
     EntryUpdated(usize),
     EntriesRemoved(Range<usize>),
     ToolAuthorizationRequired,
@@ -728,11 +735,9 @@ impl AcpThread {
         title: impl Into<SharedString>,
         connection: Rc<dyn AgentConnection>,
         project: Entity<Project>,
+        action_log: Entity<ActionLog>,
         session_id: acp::SessionId,
-        cx: &mut Context<Self>,
     ) -> Self {
-        let action_log = cx.new(|_| ActionLog::new(project.clone()));
-
         Self {
             action_log,
             shared_buffers: Default::default(),
@@ -926,6 +931,12 @@ impl AcpThread {
         cx.emit(AcpThreadEvent::NewEntry);
     }
 
+    pub fn update_title(&mut self, title: SharedString, cx: &mut Context<Self>) -> Result<()> {
+        self.title = title;
+        cx.emit(AcpThreadEvent::TitleUpdated);
+        Ok(())
+    }
+
     pub fn update_retry_status(&mut self, status: RetryStatus, cx: &mut Context<Self>) {
         cx.emit(AcpThreadEvent::Retry(status));
     }
@@ -1657,7 +1668,7 @@ mod tests {
     use super::*;
     use anyhow::anyhow;
     use futures::{channel::mpsc, future::LocalBoxFuture, select};
-    use gpui::{AsyncApp, TestAppContext, WeakEntity};
+    use gpui::{App, AsyncApp, TestAppContext, WeakEntity};
     use indoc::indoc;
     use project::{FakeFs, Fs};
     use rand::Rng as _;
@@ -2327,7 +2338,7 @@ mod tests {
             self: Rc<Self>,
             project: Entity<Project>,
             _cwd: &Path,
-            cx: &mut gpui::App,
+            cx: &mut App,
         ) -> Task<gpui::Result<Entity<AcpThread>>> {
             let session_id = acp::SessionId(
                 rand::thread_rng()
@@ -2337,8 +2348,16 @@ mod tests {
                     .collect::<String>()
                     .into(),
             );
-            let thread =
-                cx.new(|cx| AcpThread::new("Test", self.clone(), project, session_id.clone(), cx));
+            let action_log = cx.new(|_| ActionLog::new(project.clone()));
+            let thread = cx.new(|_cx| {
+                AcpThread::new(
+                    "Test",
+                    self.clone(),
+                    project,
+                    action_log,
+                    session_id.clone(),
+                )
+            });
             self.sessions.lock().insert(session_id, thread.downgrade());
             Task::ready(Ok(thread))
         }