agent: Add new panel navigation dropdown (#29539)

- [x] Ensure what appears in the dropdown is really what is accurate
- [x] Ensure keyboard navigation works:
  - [x] Switching tabs with `enter`
  - [x] Closing items from the menu item
  - [x] Opening the dropdown
  - [x] Focus assistant panel on dismiss
- [x] Add ability to close items from the dropdown menu
- [x] Persistence
- [x] Correct behavior when opening a text thread

Release Notes:

- agent: Added a navigation menu that shows the recently opened threads.
The button to see the full history view has been changed inside this
menu.

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Cole Miller <m@cole-miller.net>
Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>
Co-authored-by: Cole Miller <cole@zed.dev>

crates/assistant_context_editor/src/context_store.rs

@@ -20,14 +20,7 @@ use prompt_store::PromptBuilder;
 use regex::Regex;
 use rpc::AnyProtoClient;
 use std::sync::LazyLock;
-use std::{
-    cmp::Reverse,
-    ffi::OsStr,
-    mem,
-    path::{Path, PathBuf},
-    sync::Arc,
-    time::Duration,
-};
+use std::{cmp::Reverse, ffi::OsStr, mem, path::Path, sync::Arc, time::Duration};
 use util::{ResultExt, TryFutureExt};
 
 pub(crate) fn init(client: &AnyProtoClient) {
@@ -430,7 +423,7 @@ impl ContextStore {
 
     pub fn open_local_context(
         &mut self,
-        path: PathBuf,
+        path: Arc<Path>,
         cx: &Context<Self>,
     ) -> Task<Result<Entity<AssistantContext>>> {
         if let Some(existing_context) = self.loaded_context_for_path(&path, cx) {
@@ -478,7 +471,7 @@ impl ContextStore {
 
     pub fn delete_local_context(
         &mut self,
-        path: PathBuf,
+        path: Arc<Path>,
         cx: &mut Context<Self>,
     ) -> Task<Result<()>> {
         let fs = self.fs.clone();
@@ -501,7 +494,7 @@ impl ContextStore {
                         != Some(&path)
                 });
                 this.contexts_metadata
-                    .retain(|context| context.path != path);
+                    .retain(|context| context.path.as_ref() != path.as_ref());
             })?;
 
             Ok(())
@@ -511,7 +504,7 @@ impl ContextStore {
     fn loaded_context_for_path(&self, path: &Path, cx: &App) -> Option<Entity<AssistantContext>> {
         self.contexts.iter().find_map(|context| {
             let context = context.upgrade()?;
-            if context.read(cx).path() == Some(path) {
+            if context.read(cx).path().map(Arc::as_ref) == Some(path) {
                 Some(context)
             } else {
                 None
@@ -794,7 +787,7 @@ impl ContextStore {
                     {
                         contexts.push(SavedContextMetadata {
                             title: title.to_string(),
-                            path,
+                            path: path.into(),
                             mtime: metadata.mtime.timestamp_for_user().into(),
                         });
                     }