agent: Support adding selection as context (#28964)

https://github.com/user-attachments/assets/42ebe911-3392-48f7-8583-caab285aca09

Release Notes:

- agent: Support adding selections via @selection or `assistant: Quote
selection` as context

crates/assistant_context_editor/src/context_editor.rs

@@ -8,8 +8,8 @@ use assistant_slash_commands::{
 use client::{proto, zed_urls};
 use collections::{BTreeSet, HashMap, HashSet, hash_map};
 use editor::{
-    Anchor, Editor, EditorEvent, MenuInlineCompletionsPolicy, ProposedChangeLocation,
-    ProposedChangesEditor, RowExt, ToOffset as _, ToPoint,
+    Anchor, Editor, EditorEvent, MenuInlineCompletionsPolicy, MultiBuffer, MultiBufferSnapshot,
+    ProposedChangeLocation, ProposedChangesEditor, RowExt, ToOffset as _, ToPoint,
     actions::{MoveToEndOfLine, Newline, ShowCompletions},
     display_map::{
         BlockContext, BlockId, BlockPlacement, BlockProperties, BlockStyle, Crease, CreaseMetadata,
@@ -155,7 +155,8 @@ pub trait AssistantPanelDelegate {
     fn quote_selection(
         &self,
         workspace: &mut Workspace,
-        creases: Vec<(String, String)>,
+        selection_ranges: Vec<Range<Anchor>>,
+        buffer: Entity<MultiBuffer>,
         window: &mut Window,
         cx: &mut Context<Workspace>,
     );
@@ -1800,23 +1801,42 @@ impl ContextEditor {
             return;
         };
 
-        let Some(creases) = selections_creases(workspace, cx) else {
+        let Some((selections, buffer)) = maybe!({
+            let editor = workspace
+                .active_item(cx)
+                .and_then(|item| item.act_as::<Editor>(cx))?;
+
+            let buffer = editor.read(cx).buffer().clone();
+            let snapshot = buffer.read(cx).snapshot(cx);
+            let selections = editor.update(cx, |editor, cx| {
+                editor
+                    .selections
+                    .all_adjusted(cx)
+                    .into_iter()
+                    .map(|s| snapshot.anchor_after(s.start)..snapshot.anchor_before(s.end))
+                    .collect::<Vec<_>>()
+            });
+            Some((selections, buffer))
+        }) else {
             return;
         };
 
-        if creases.is_empty() {
+        if selections.is_empty() {
             return;
         }
 
-        assistant_panel_delegate.quote_selection(workspace, creases, window, cx);
+        assistant_panel_delegate.quote_selection(workspace, selections, buffer, window, cx);
     }
 
-    pub fn quote_creases(
+    pub fn quote_ranges(
         &mut self,
-        creases: Vec<(String, String)>,
+        ranges: Vec<Range<Point>>,
+        snapshot: MultiBufferSnapshot,
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
+        let creases = selections_creases(ranges, snapshot, cx);
+
         self.editor.update(cx, |editor, cx| {
             editor.insert("\n", window, cx);
             for (text, crease_title) in creases {