agent_ui: Add skills menu item in message editor's context menu (#57407)

Closes AI-295

This PR adds a skills submenu within the "add context" menu in the agent
panel's message editor. This will hopefully be yet another way to find
skills in the app.

<img width="600" alt="Screenshot 2026-05-21 at 11  24@2x"
src="https://github.com/user-attachments/assets/43652081-3929-4ca0-a32b-464077d84dd5"
/>

Release Notes:

- N/A

crates/agent_ui/src/conversation_view/thread_view.rs

@@ -12,6 +12,7 @@ use cloud_api_types::{SubmitAgentThreadFeedbackBody, SubmitAgentThreadFeedbackCo
 use editor::actions::OpenExcerpts;
 use feature_flags::AcpBetaFeatureFlag;
 
+use crate::completion_provider::AvailableSkill;
 use crate::message_editor::SharedSessionCapabilities;
 
 use gpui::List;
@@ -4157,6 +4158,8 @@ impl ThreadView {
         let session_capabilities = self.session_capabilities.read();
         let supports_images = session_capabilities.supports_images();
         let supports_embedded_context = session_capabilities.supports_embedded_context();
+        let available_skills = session_capabilities.completion_skills();
+        drop(session_capabilities);
 
         let has_editor_selection = workspace
             .upgrade()
@@ -4180,7 +4183,6 @@ impl ThreadView {
 
         ContextMenu::build(window, cx, move |menu, _window, _cx| {
             menu.key_context("AddContextMenu")
-                .header("Context")
                 .item(
                     ContextMenuEntry::new("Files & Directories")
                         .icon(IconName::File)
@@ -4226,21 +4228,19 @@ impl ThreadView {
                             }
                         }),
                 )
-                .item(
-                    ContextMenuEntry::new("Skills")
-                        .icon(IconName::Sparkle)
-                        .icon_color(Color::Muted)
-                        .icon_size(IconSize::XSmall)
-                        .handler({
-                            let message_editor = message_editor.clone();
-                            move |window, cx| {
-                                message_editor.focus_handle(cx).focus(window, cx);
-                                message_editor.update(cx, |editor, cx| {
-                                    editor.insert_context_type("skill", window, cx);
-                                });
+                .when(!available_skills.is_empty(), |this| {
+                    this.submenu_with_colored_icon("Skills", IconName::Sparkle, Color::Muted, {
+                        let message_editor = message_editor.clone();
+                        let available_skills = available_skills.clone();
+                        move |mut menu, _window, _cx| {
+                            for skill in &available_skills {
+                                menu = menu
+                                    .item(Self::skill_menu_entry(skill, message_editor.clone()));
                             }
-                        }),
-                )
+                            menu
+                        }
+                    })
+                })
                 .item(
                     ContextMenuEntry::new("Image")
                         .icon(IconName::Image)
@@ -4289,6 +4289,25 @@ impl ThreadView {
         })
     }
 
+    fn skill_menu_entry(
+        skill: &AvailableSkill,
+        message_editor: Entity<crate::message_editor::MessageEditor>,
+    ) -> ContextMenuEntry {
+        let label = format!("{} ({})", skill.name, skill.source);
+        let skill = skill.clone();
+
+        ContextMenuEntry::new(label)
+            .icon(IconName::Sparkle)
+            .icon_color(Color::Muted)
+            .icon_size(IconSize::XSmall)
+            .handler(move |window, cx| {
+                message_editor.focus_handle(cx).focus(window, cx);
+                message_editor.update(cx, |editor, cx| {
+                    editor.insert_skill_crease(&skill, window, cx);
+                });
+            })
+    }
+
     fn render_follow_toggle(&self, cx: &mut Context<Self>) -> impl IntoElement {
         let following = self.is_following(cx);
 

crates/agent_ui/src/message_editor.rs

@@ -1514,6 +1514,61 @@ impl MessageEditor {
             .detach_and_log_err(cx);
     }
 
+    pub fn insert_skill_crease(
+        &mut self,
+        skill: &AvailableSkill,
+        window: &mut Window,
+        cx: &mut Context<Self>,
+    ) {
+        let Some(workspace) = self.workspace.upgrade() else {
+            return;
+        };
+
+        let mention_uri = MentionUri::Skill {
+            name: skill.name.to_string(),
+            source: skill.source.to_string(),
+            skill_file_path: skill.skill_file_path.clone(),
+        };
+
+        let link_text = mention_uri.as_link().to_string();
+        let content_len = link_text.len();
+        let mention_text = format!("{} ", link_text);
+        let crease_text: SharedString = mention_uri.name().into();
+
+        let start_anchor = self.editor.update(cx, |editor, cx| {
+            let snapshot = editor.buffer().read(cx).snapshot(cx);
+            let buffer_snapshot = snapshot.as_singleton()?;
+            let cursor = editor.selections.newest_anchor().start;
+            let text_anchor = snapshot
+                .anchor_to_buffer_anchor(cursor)?
+                .0
+                .bias_left(buffer_snapshot);
+
+            editor.insert(&mention_text, window, cx);
+            Some(text_anchor)
+        });
+
+        let Some(start_anchor) = start_anchor else {
+            return;
+        };
+
+        self.mention_set
+            .update(cx, |mention_set, cx| {
+                mention_set.confirm_mention_completion(
+                    crease_text,
+                    start_anchor,
+                    content_len,
+                    mention_uri,
+                    false,
+                    self.editor.clone(),
+                    &workspace,
+                    window,
+                    cx,
+                )
+            })
+            .detach();
+    }
+
     pub(crate) fn insert_selections(
         &mut self,
         selection: AgentContextSelection,