agent: Improve attached context display and show hovers for symbol / selection / rules / thread (#29551)

* Brings back hover popover of selection context.

* Adds hover popover for symbol, rules, and thread context.

* Makes context attached to messages display the names / content at
attachment time.

* Adds the file name as the displayed parent of symbol context.

* Brings back `impl Component for AddedContext`

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>

crates/agent/src/active_thread.rs

@@ -1,4 +1,4 @@
-use crate::context::{AgentContext, RULES_ICON};
+use crate::context::{AgentContextHandle, RULES_ICON};
 use crate::context_picker::MentionLink;
 use crate::thread::{
     LastRestoreCheckpoint, MessageId, MessageSegment, Thread, ThreadError, ThreadEvent,
@@ -1491,19 +1491,13 @@ impl ActiveThread {
 
         let workspace = self.workspace.clone();
         let thread = self.thread.read(cx);
-        let prompt_store = self.thread_store.read(cx).prompt_store().as_ref();
 
         // Get all the data we need from thread before we start using it in closures
         let checkpoint = thread.checkpoint_for_message(message_id);
-        let added_context = if let Some(workspace) = workspace.upgrade() {
-            let project = workspace.read(cx).project().read(cx);
-            thread
-                .context_for_message(message_id)
-                .flat_map(|context| AddedContext::new(context.clone(), prompt_store, project, cx))
-                .collect::<Vec<_>>()
-        } else {
-            return Empty.into_any();
-        };
+        let added_context = thread
+            .context_for_message(message_id)
+            .map(|context| AddedContext::new_attached(context, cx))
+            .collect::<Vec<_>>();
 
         let tool_uses = thread.tool_uses_for_message(message_id, cx);
         let has_tool_uses = !tool_uses.is_empty();
@@ -1713,7 +1707,7 @@ impl ActiveThread {
                 .when(!added_context.is_empty(), |parent| {
                     parent.child(h_flex().flex_wrap().gap_1().children(
                         added_context.into_iter().map(|added_context| {
-                            let context = added_context.context.clone();
+                            let context = added_context.handle.clone();
                             ContextPill::added(added_context, false, false, None).on_click(Rc::new(
                                 cx.listener({
                                     let workspace = workspace.clone();
@@ -3188,13 +3182,13 @@ impl Render for ActiveThread {
 }
 
 pub(crate) fn open_context(
-    context: &AgentContext,
+    context: &AgentContextHandle,
     workspace: Entity<Workspace>,
     window: &mut Window,
     cx: &mut App,
 ) {
     match context {
-        AgentContext::File(file_context) => {
+        AgentContextHandle::File(file_context) => {
             if let Some(project_path) = file_context.project_path(cx) {
                 workspace.update(cx, |workspace, cx| {
                     workspace
@@ -3204,7 +3198,7 @@ pub(crate) fn open_context(
             }
         }
 
-        AgentContext::Directory(directory_context) => {
+        AgentContextHandle::Directory(directory_context) => {
             let entry_id = directory_context.entry_id;
             workspace.update(cx, |workspace, cx| {
                 workspace.project().update(cx, |_project, cx| {
@@ -3213,7 +3207,7 @@ pub(crate) fn open_context(
             })
         }
 
-        AgentContext::Symbol(symbol_context) => {
+        AgentContextHandle::Symbol(symbol_context) => {
             let buffer = symbol_context.buffer.read(cx);
             if let Some(project_path) = buffer.project_path(cx) {
                 let snapshot = buffer.snapshot();
@@ -3223,7 +3217,7 @@ pub(crate) fn open_context(
             }
         }
 
-        AgentContext::Selection(selection_context) => {
+        AgentContextHandle::Selection(selection_context) => {
             let buffer = selection_context.buffer.read(cx);
             if let Some(project_path) = buffer.project_path(cx) {
                 let snapshot = buffer.snapshot();
@@ -3234,11 +3228,11 @@ pub(crate) fn open_context(
             }
         }
 
-        AgentContext::FetchedUrl(fetched_url_context) => {
+        AgentContextHandle::FetchedUrl(fetched_url_context) => {
             cx.open_url(&fetched_url_context.url);
         }
 
-        AgentContext::Thread(thread_context) => workspace.update(cx, |workspace, cx| {
+        AgentContextHandle::Thread(thread_context) => workspace.update(cx, |workspace, cx| {
             if let Some(panel) = workspace.panel::<AssistantPanel>(cx) {
                 panel.update(cx, |panel, cx| {
                     let thread_id = thread_context.thread.read(cx).id().clone();
@@ -3249,14 +3243,14 @@ pub(crate) fn open_context(
             }
         }),
 
-        AgentContext::Rules(rules_context) => window.dispatch_action(
+        AgentContextHandle::Rules(rules_context) => window.dispatch_action(
             Box::new(OpenRulesLibrary {
                 prompt_to_select: Some(rules_context.prompt_id.0),
             }),
             cx,
         ),
 
-        AgentContext::Image(_) => {}
+        AgentContextHandle::Image(_) => {}
     }
 }