From 681c094b0cafc5e2d7d17ef4e4399ab73ee807b0 Mon Sep 17 00:00:00 2001
From: Arthur Belleville <arthur.belleville@datadoghq.com>
Date: Sun, 17 May 2026 12:47:21 +0200
Subject: [PATCH] fix(17): skip own-user SSE messages in JS to eliminate
 left-then-right flash
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The server-side flush didn't eliminate the race because browser HTMX and SSE
event processing are inherently async.

Real fix: embed data-current-user-id on #discussion-tab (from DiscussionTabData.
CurrentUserID). The SSE handler now skips any event whose authorUserId matches
the current user — those messages are always delivered via HTMX (IsOwn=true,
right-aligned). SSE only appends messages from other users.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
---
 backend/internal/web/handlers_discussion.go | 5 ++++-
 backend/static/discussion-sse.js            | 6 ++++++
 backend/templates/discussion.templ          | 2 +-
 backend/templates/discussion_forms.go       | 3 ++-
 4 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/backend/internal/web/handlers_discussion.go b/backend/internal/web/handlers_discussion.go
index 07ca9a9..062a3ec 100644
--- a/backend/internal/web/handlers_discussion.go
+++ b/backend/internal/web/handlers_discussion.go
@@ -29,7 +29,10 @@ func loadDiscussionTabData(w http.ResponseWriter, r *http.Request, q *sqlc.Queri
 		http.Error(w, "internal server error", http.StatusInternalServerError)
 		return templates.DiscussionTabData{}, false
 	}
-	data := templates.DiscussionTabData{Messages: templates.DiscussionMessagesFromRows(rows, currentUserID)}
+	data := templates.DiscussionTabData{
+		Messages:      templates.DiscussionMessagesFromRows(rows, currentUserID),
+		CurrentUserID: currentUserID,
+	}
 	return data, true
 }
 
diff --git a/backend/static/discussion-sse.js b/backend/static/discussion-sse.js
index 6c8059b..7834be2 100644
--- a/backend/static/discussion-sse.js
+++ b/backend/static/discussion-sse.js
@@ -42,6 +42,12 @@
     if (!event || !event.messageId || !event.messageHtml || messageExists(event.messageId)) {
       return;
     }
+    // Skip messages authored by the current user — HTMX already appended them
+    // with IsOwn=true. Let SSE handle only messages from other users.
+    var currentUserId = container.dataset.currentUserId;
+    if (currentUserId && event.authorUserId === currentUserId) {
+      return;
+    }
     var list = ensureMessageList(container);
     if (!list) return;
 
diff --git a/backend/templates/discussion.templ b/backend/templates/discussion.templ
index de981c5..d830f19 100644
--- a/backend/templates/discussion.templ
+++ b/backend/templates/discussion.templ
@@ -8,7 +8,7 @@ import (
 )
 
 templ DiscussionTabFragment(tablo sqlc.Tablo, data DiscussionTabData, form DiscussionForm, errs DiscussionErrors, csrfToken string) {
-	<div id="discussion-tab" class="space-y-6" data-discussion-stream-url={ DiscussionStreamURL(tablo.ID) }>
+	<div id="discussion-tab" class="space-y-6" data-discussion-stream-url={ DiscussionStreamURL(tablo.ID) } data-current-user-id={ data.CurrentUserID.String() }>
 		<div class="flex flex-wrap items-start justify-between gap-3">
 			<div>
 				<h2 class="text-2xl font-semibold leading-tight text-slate-900">Discussion</h2>
diff --git a/backend/templates/discussion_forms.go b/backend/templates/discussion_forms.go
index 7a0ba0a..2ae02d0 100644
--- a/backend/templates/discussion_forms.go
+++ b/backend/templates/discussion_forms.go
@@ -29,7 +29,8 @@ type DiscussionMessageView struct {
 }
 
 type DiscussionTabData struct {
-	Messages []DiscussionMessageView
+	Messages      []DiscussionMessageView
+	CurrentUserID uuid.UUID
 }
 
 type TabloCardView struct {