fix: isolate attachment submission state

src/pages/Chat/CodingChatPanel.tsx

@@ -301,7 +301,8 @@ export function CodingChatPanel({
   ]);
 
   const handleAddFiles = useCallback((files: File[]) => {
-    if (!draftKey) return;
+    if (!draftKey
+      || (targetConversationId && submissionFlightsRef.current.has(targetConversationId))) return;
     const accepted: LocalComposerAttachment[] = [];
     const remaining = Math.max(0, CODING_ATTACHMENT_MAX_COUNT - localAttachments.length);
     let validationError = files.length > remaining
@@ -335,10 +336,11 @@ export function CodingChatPanel({
       ...current,
       [draftKey]: [...(current[draftKey] ?? []), ...accepted],
     }));
-  }, [draftKey, localAttachments.length]);
+  }, [draftKey, localAttachments.length, targetConversationId]);
 
   const handleRemoveAttachment = useCallback((id: string) => {
-    if (!draftKey) return;
+    if (!draftKey
+      || (targetConversationId && submissionFlightsRef.current.has(targetConversationId))) return;
     setAttachmentsByDraftKey((current) => {
       const attachment = current[draftKey]?.find((item) => item.id === id);
       if (attachment) URL.revokeObjectURL(attachment.previewUrl);
@@ -349,7 +351,12 @@ export function CodingChatPanel({
     });
     uploadedAttachmentsRef.current.delete(id);
     uploadFlightsRef.current.delete(id);
-  }, [draftKey]);
+    setSubmissionErrors((current) => {
+      const next = { ...current };
+      delete next[draftKey];
+      return next;
+    });
+  }, [draftKey, targetConversationId]);
 
   const prepareAttachments = useCallback(async (
     attachments: LocalComposerAttachment[],