diff --git a/backend/internal/web/handlers_discussion_test.go b/backend/internal/web/handlers_discussion_test.go
index 86dac65..cdd3e64 100644
--- a/backend/internal/web/handlers_discussion_test.go
+++ b/backend/internal/web/handlers_discussion_test.go
@@ -472,6 +472,32 @@ func TestDiscussionBrokerUnregistersOnCancel(t *testing.T) {
 	}
 }
 
+func TestDiscussionStaticScriptSuppressesDuplicateMessageSwap(t *testing.T) {
+	js, err := os.ReadFile("../../static/discussion-sse.js")
+	if err != nil {
+		t.Fatalf("read discussion-sse.js: %v", err)
+	}
+	script := string(js)
+	for _, want := range []string{"htmx:beforeSwap", "messageIdFromHTML", "preventDefault()"} {
+		if !strings.Contains(script, want) {
+			t.Fatalf("discussion script missing %q for duplicate swap suppression; script: %.1200s", want, script)
+		}
+	}
+}
+
+func TestDiscussionStaticScriptClearsComposerAfterSuccessfulPost(t *testing.T) {
+	js, err := os.ReadFile("../../static/discussion-sse.js")
+	if err != nil {
+		t.Fatalf("read discussion-sse.js: %v", err)
+	}
+	script := string(js)
+	for _, want := range []string{"htmx:afterRequest", "discussion-message-body", ".reset()"} {
+		if !strings.Contains(script, want) {
+			t.Fatalf("discussion script missing %q for composer reset; script: %.1200s", want, script)
+		}
+	}
+}
+
 func TestTablosListDiscussionUnreadBadge(t *testing.T) {
 	pool, cleanup := setupTestDB(t)
 	defer cleanup()
diff --git a/backend/static/discussion-sse.js b/backend/static/discussion-sse.js
index 475f440..56024a1 100644
--- a/backend/static/discussion-sse.js
+++ b/backend/static/discussion-sse.js
@@ -3,6 +3,18 @@
     return Boolean(document.querySelector('[data-message-id="' + CSS.escape(messageId) + '"]'));
   }
 
+  function isDiscussionMessageForm(element) {
+    return Boolean(element && element.matches && element.matches('form[action$="/discussion/messages"]'));
+  }
+
+  function messageIdFromHTML(html) {
+    if (!html) return "";
+    var template = document.createElement("template");
+    template.innerHTML = html.trim();
+    var message = template.content.querySelector("[data-message-id]");
+    return message ? message.dataset.messageId : "";
+  }
+
   function ensureMessageList(container) {
     var messages = container.querySelector("#discussion-messages");
     if (!messages) return null;
@@ -52,4 +64,21 @@
 
   document.addEventListener("DOMContentLoaded", connectDiscussionStreams);
   document.body.addEventListener("htmx:afterSwap", connectDiscussionStreams);
+  document.body.addEventListener("htmx:beforeSwap", function (event) {
+    if (!isDiscussionMessageForm(event.detail && event.detail.elt)) return;
+
+    var messageId = messageIdFromHTML(event.detail.xhr && event.detail.xhr.responseText);
+    if (messageId && messageExists(messageId)) {
+      event.detail.shouldSwap = false;
+      event.preventDefault();
+    }
+  });
+  document.body.addEventListener("htmx:afterRequest", function (event) {
+    var form = event.detail && event.detail.elt;
+    if (!isDiscussionMessageForm(form) || !event.detail.successful) return;
+
+    form.reset();
+    var textarea = form.querySelector("#discussion-message-body");
+    if (textarea) textarea.value = "";
+  });
 })();