agent: Patch image format bug (#45978)

Mason Palmer , versecafe , and MrSubidubi created 3 days ago

Closes #44694

Release Notes:

- Fixed images being converted to png but retaining old format

## Before:
<img width="574" height="327" alt="Screenshot 2026-01-02 at 5 34 24 PM"
src="https://github.com/user-attachments/assets/92331939-cebc-4f53-99fc-10d5181cf87e"
/>

## After:
<img width="638" height="489" alt="Screenshot 2026-01-02 at 5 34 36 PM"
src="https://github.com/user-attachments/assets/47c05906-fa56-4a53-abd4-790c42230772"
/>

---------

Co-authored-by: versecafe <[e-mail]>
Co-authored-by: MrSubidubi <[e-mail]>

Change summary

crates/agent_ui/src/mention_set.rs   | 6 ++----
crates/language_model/src/request.rs | 3 +++
2 files changed, 5 insertions(+), 4 deletions(-)

Detailed changes

crates/agent_ui/src/mention_set.rs

@@ -297,14 +297,13 @@ impl MentionSet {
             return cx.spawn(async move |_, cx| {
                 let image = task.await?;
                 let image = image.update(cx, |image, _| image.image.clone());
-                let format = image.format;
                 let image = cx
                     .update(|cx| LanguageModelImage::from_image(image, cx))
                     .await;
                 if let Some(image) = image {
                     Ok(Mention::Image(MentionImage {
                         data: image.source,
-                        format,
+                        format: LanguageModelImage::FORMAT,
                     }))
                 } else {
                     Err(anyhow!("Failed to convert image"))
@@ -672,7 +671,6 @@ pub(crate) fn paste_images_as_context(
             };
             let task = cx
                 .spawn(async move |cx| {
-                    let format = image.format;
                     let image = cx
                         .update(|_, cx| LanguageModelImage::from_image(image, cx))
                         .map_err(|e| e.to_string())?
@@ -681,7 +679,7 @@ pub(crate) fn paste_images_as_context(
                     if let Some(image) = image {
                         Ok(Mention::Image(MentionImage {
                             data: image.source,
-                            format,
+                            format: LanguageModelImage::FORMAT,
                         }))
                     } else {
                         Err("Failed to convert image".into())

crates/language_model/src/request.rs

@@ -92,6 +92,9 @@ const DEFAULT_IMAGE_MAX_BYTES: usize = 5 * 1024 * 1024;
 const MAX_IMAGE_DOWNSCALE_PASSES: usize = 8;
 
 impl LanguageModelImage {
+    // All language model images are encoded as PNGs.
+    pub const FORMAT: ImageFormat = ImageFormat::Png;
+
     pub fn empty() -> Self {
         Self {
             source: "".into(),