feat(image): pass reference images to GPT image model for edits

Server: forward canvas/reference images to the image model so extract,
continue, and edit requests stay faithful to the source product.
- Add ImageRequestOptions.Images and route requests with inputs to the
  /v1/images/edits endpoint, via multipart upload (default) or JSON
  image_url payload, selectable through Agent.Image.InputImageTransport.
- Extract reference URLs from prompt directives, inline @image tokens,
  and chat message image/mask contents; fold them into the idempotency
  key and prepend a reference-fidelity instruction to the prompt.

Frontend:
- Shrink CanvasToast to a compact top pill.
- Paste an internal transparent clipboard node instead of re-uploading
  when it matches the clipboard image.
- Keep agent-project polling alive on stream error while streaming.

frontend/src/ui/pages/CanvasWorkspace/canvas/hooks/useGenerationStream.ts

@@ -233,8 +233,9 @@ export function useGenerationStream({
           closeRef.current = null;
         },
         onError: (nextError) => {
-          if (closeAgentProjectPollRef.current) {
+          if (streamingRef.current === streamKey) {
             closeRef.current = null;
+            startAgentProjectPolling(nextProjectId, threadId);
             return;
           }
           completeChannel(channel);
@@ -243,7 +244,6 @@ export function useGenerationStream({
           closeRef.current = null;
         }
       });
-      startAgentProjectPolling(nextProjectId, threadId);
     },
     [appendThinkingMessage, applyProject, completeChannel, toUserMessageText, messages.generateError, messages.generateTimeout, setError, startAgentProjectPolling, startGeneratorTaskPolling]
   );
@@ -306,8 +306,9 @@ export function useGenerationStream({
           closeRef.current = null;
         },
         onError: (nextError) => {
-          if (closeAgentProjectPollRef.current) {
+          if (streamingRef.current === streamKey) {
             closeRef.current = null;
+            startAgentProjectPolling(nextProjectId, payload.threadId);
             return;
           }
           completeChannel(channel);
@@ -316,7 +317,6 @@ export function useGenerationStream({
           closeRef.current = null;
         }
       });
-      startAgentProjectPolling(nextProjectId, payload.threadId);
     },
     [appendThinkingMessage, applyProject, completeChannel, toUserMessageText, messages.generateError, messages.generateTimeout, setError, startAgentProjectPolling, startGeneratorTaskPolling]
   );

frontend/src/ui/pages/CanvasWorkspace/index.tsx

@@ -1843,9 +1843,9 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
       .catch(() => showCanvasToast(t("clipboardCopyFailed"), "error"));
   };
 
-  const pasteNode = () => {
-    if (!clipboardNode) return;
-    const copy = cloneCanvasNode(clipboardNode, cryptoFallbackId());
+  const pasteNode = (sourceNode = clipboardNode) => {
+    if (!sourceNode) return;
+    const copy = cloneCanvasNode(sourceNode, cryptoFallbackId());
     setNodes((current) => [...current, copy]);
     selectOnlyNode(copy.id);
     setDirty(true);
@@ -2145,11 +2145,25 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
       if (isEditableShortcutTarget(event.target)) return;
 
       const imageFiles = event.clipboardData ? dataTransferImageFiles(event.clipboardData, "clipboard-image") : [];
-      if (imageFiles.length > 0) {
-        event.preventDefault();
+      const pasteImageFiles = () => {
         const pointer = lastCanvasPointerRef.current;
         const anchor = pointer ? canvasPointFromClient(pointer.clientX, pointer.clientY) : canvasCenterPoint();
         void uploadImagesToCanvas(imageFiles, anchor);
+      };
+      if (clipboardNode && imageFiles.length > 0 && isTransparentClipboardNode(clipboardNode)) {
+        event.preventDefault();
+        void shouldUseInternalClipboardNode(clipboardNode, imageFiles).then((useInternalNode) => {
+          if (useInternalNode) {
+            pasteNode(clipboardNode);
+            return;
+          }
+          pasteImageFiles();
+        });
+        return;
+      }
+      if (imageFiles.length > 0) {
+        event.preventDefault();
+        pasteImageFiles();
         return;
       }