feat(composer): carry reference image names and submit on Enter

Propagate an optional imageName through the agent content pipeline
(frontend types → API → domain → prompt building) so reference images
render with their name instead of a bare "image" label.

Also switch PromptComposer to submit on plain Enter (Shift+Enter for
newline, IME-safe) and add a submitDisabled guard wired from the canvas
and home composers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/ui/components/CanvasAgentComposer/index.tsx

@@ -190,6 +190,7 @@ export const CanvasAgentComposer = forwardRef<PromptComposerHandle, CanvasAgentC
         onAnnotationPreviewChange={onAnnotationPreviewChange}
         onPasteFile={onUploadFile}
         onSubmit={onSubmit}
+        submitDisabled={generating || !canSubmit}
       />
       {previewSlot}
       <div className="assistant-composer-toolbar">

frontend/src/ui/components/PromptComposer/index.tsx

@@ -632,6 +632,7 @@ export const PromptComposer = forwardRef<
     onAnnotationPreviewChange?: (preview: AnnotationPreviewRequest | null) => void;
     onPasteFile?: (file: File | null) => void | Promise<void>;
     onSubmit?: () => void;
+    submitDisabled?: boolean;
   }
 >(function PromptComposer(
   {
@@ -648,7 +649,8 @@ export const PromptComposer = forwardRef<
     onAnnotationsChange,
     onAnnotationPreviewChange,
     onPasteFile,
-    onSubmit
+    onSubmit,
+    submitDisabled = false
   },
   ref
 ) {
@@ -883,7 +885,8 @@ export const PromptComposer = forwardRef<
           }
           return {
             type: "image",
-            imageUrl: part.reference.publicUrl
+            imageUrl: part.reference.publicUrl,
+            imageName: part.reference.name
           };
         })
         .filter((part): part is AgentContent => Boolean(part));
@@ -1067,9 +1070,10 @@ export const PromptComposer = forwardRef<
             }
           }
         }
-        if ((event.metaKey || event.ctrlKey) && event.key === "Enter") {
+        const isComposing = event.nativeEvent.isComposing || event.keyCode === 229;
+        if (event.key === "Enter" && !event.shiftKey && !isComposing) {
           event.preventDefault();
-          onSubmit?.();
+          if (!submitDisabled) onSubmit?.();
         }
       }}
       onPaste={handlePaste}