agent_ui: Restore hover previews for image mentions (#58165)

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes https://github.com/zed-industries/zed/issues/58153

Release Notes:

- Agent: Fixed image previews not being displayed after submitting a
prompt and then hovering the mentioned image.

crates/agent_ui/src/message_editor.rs

@@ -13,6 +13,7 @@ use acp_thread::MentionUri;
 use agent::ThreadStore;
 use agent_client_protocol::schema as acp;
 use anyhow::{Result, anyhow};
+use base64::Engine as _;
 use editor::{
     Addon, AnchorRangeExt, ContextMenuOptions, Editor, EditorElement, EditorEvent, EditorMode,
     EditorStyle, Inlay, MultiBuffer, MultiBufferOffset, MultiBufferSnapshot, ToOffset,
@@ -24,8 +25,8 @@ use editor::{
 use futures::{FutureExt as _, future::join_all};
 use gpui::{
     AppContext, ClipboardEntry, ClipboardItem, Context, Entity, EventEmitter, FocusHandle,
-    Focusable, ImageFormat, KeyContext, SharedString, Subscription, Task, TaskExt, TextStyle,
-    WeakEntity,
+    Focusable, Image, ImageFormat, KeyContext, SharedString, Subscription, Task, TaskExt,
+    TextStyle, WeakEntity,
 };
 use language::{Buffer, language_settings::InlayHintKind};
 use parking_lot::RwLock;
@@ -1815,6 +1816,7 @@ impl MessageEditor {
         for (range, mention_uri, mention) in mentions {
             let adjusted_start = insertion_start + range.start;
             let anchor = snapshot.anchor_before(MultiBufferOffset(adjusted_start));
+            let image_preview = image_preview_task_for_mention(&mention);
             let Some((crease_id, tx, crease_entity)) = insert_crease_for_mention(
                 snapshot.anchor_to_buffer_anchor(anchor).unwrap().0,
                 range.end - range.start,
@@ -1823,7 +1825,7 @@ impl MessageEditor {
                 mention_uri.tooltip_text(),
                 Some(mention_uri.clone()),
                 Some(self.workspace.clone()),
-                None,
+                image_preview,
                 self.editor.clone(),
                 window,
                 cx,
@@ -2094,6 +2096,31 @@ fn build_chunks_from_creases(
     (chunks, tracked_buffers)
 }
 
+fn image_preview_task_for_mention(
+    mention: &Mention,
+) -> Option<futures::future::Shared<Task<Result<Arc<Image>, String>>>> {
+    let Mention::Image(mention_image) = mention else {
+        return None;
+    };
+
+    let bytes =
+        match base64::engine::general_purpose::STANDARD.decode(mention_image.data.as_bytes()) {
+            Ok(bytes) => bytes,
+            Err(error) => {
+                log::error!("failed to decode image mention: {error}");
+                return None;
+            }
+        };
+
+    Some(
+        Task::ready(Ok::<Arc<Image>, String>(Arc::new(Image::from_bytes(
+            mention_image.format,
+            bytes,
+        ))))
+        .shared(),
+    )
+}
+
 fn mention_to_content_block(
     uri: &MentionUri,
     mention: Option<&Mention>,