diff --git a/convex/tickets.ts b/convex/tickets.ts
index c273960..bd7bf00 100644
--- a/convex/tickets.ts
+++ b/convex/tickets.ts
@@ -778,6 +778,15 @@ export const addComment = mutation({
       throw new ConvexError("Apenas administradores e agentes podem registrar comentários internos")
     }
 
+    // Regra: a equipe (ADMIN/AGENT/MANAGER) só pode comentar se o ticket tiver responsável.
+    // O solicitante (colaborador) pode comentar sempre.
+    const isRequester = String(ticketDoc.requesterId) === String(author._id)
+    const isStaff = normalizedRole === "ADMIN" || normalizedRole === "AGENT" || normalizedRole === "MANAGER"
+    const hasAssignee = Boolean(ticketDoc.assigneeId)
+    if (!isRequester && isStaff && !hasAssignee) {
+      throw new ConvexError("Somente é possível comentar quando o chamado possui um responsável.")
+    }
+
     if (ticketDoc.requesterId === args.authorId) {
       // O próprio solicitante pode comentar seu ticket.
       // Comentários internos já são bloqueados acima para quem não é STAFF.
diff --git a/src/components/tickets/ticket-comments.rich.tsx b/src/components/tickets/ticket-comments.rich.tsx
index 8eafed7..849ef8c 100644
--- a/src/components/tickets/ticket-comments.rich.tsx
+++ b/src/components/tickets/ticket-comments.rich.tsx
@@ -36,6 +36,10 @@ export function TicketComments({ ticket }: TicketCommentsProps) {
   const { convexUserId, isStaff, role } = useAuth()
   const normalizedRole = role ?? null
   const canSeeInternalComments = normalizedRole === "admin" || normalizedRole === "agent"
+  const hasAssignee = Boolean(ticket.assignee)
+  const isRequester = convexUserId ? ticket.requester.id === convexUserId : false
+  const canStaffComment = hasAssignee
+  const canComment = isRequester || (isStaff && canStaffComment)
   const addComment = useMutation(api.tickets.addComment)
   const removeAttachment = useMutation(api.tickets.removeCommentAttachment)
   const updateComment = useMutation(api.tickets.updateComment)
@@ -360,12 +364,18 @@ export function TicketComments({ ticket }: TicketCommentsProps) {
             )
           })
         )}
+        {!canComment && (
+          <div className="rounded-xl border border-amber-200 bg-amber-50 px-3 py-2 text-sm text-amber-700">
+            Atribua um responsável ao chamado para que a equipe possa comentar.
+          </div>
+        )}
         <form onSubmit={handleSubmit} className="mt-4 space-y-3">
-          <RichTextEditor value={body} onChange={setBody} placeholder="Escreva um comentário..." />
+          <RichTextEditor value={body} onChange={setBody} placeholder="Escreva um comentário..." className="rounded-2xl border border-slate-200" disabled={!canComment} />
           <Dropzone
             onUploaded={(files) => setAttachmentsToSend((prev) => [...prev, ...files])}
             currentFileCount={attachmentsToSend.length}
             currentTotalBytes={attachmentsToSendTotalBytes}
+            disabled={!canComment}
           />
           {attachmentsToSend.length > 0 ? (
             <div className="grid max-w-xl grid-cols-[repeat(auto-fill,minmax(96px,1fr))] gap-3">
@@ -477,7 +487,7 @@ export function TicketComments({ ticket }: TicketCommentsProps) {
                 </Select>
               </div>
             </div>
-            <Button type="submit" size="sm" className={submitButtonClass}>
+            <Button type="submit" size="sm" className={submitButtonClass} disabled={!canComment}>
               Enviar
             </Button>
           </div>