fix(17): address all code review findings

- CR-01: add id="discussion-message-list" to .divide-y; change hx-target
  to #discussion-message-list so HTMX appends inside the list, not after it.
  Always render the list div so the target exists even when messages is empty.
- WR-01: SSE broadcast now renders IsOwn=false for all recipients so other
  users don't receive the sender's right-aligned bubble
- WR-02: add HX-Retarget/HX-Reswap headers on 422 and 500 error responses
  so validation errors reach the composer form in the DOM
- WR-03: replace hardcoded rgba(128,78,236,0.10) with color-mix() using
  the --color-brand-primary token
- WR-04: remove hardcoded "1 participant" subtitle (no participant count in data)
- IN-02: DiscussionMessageFromRow now accepts currentUserID uuid.UUID (matching
  DiscussionMessagesFromRows) instead of a pre-computed bool

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

backend/internal/web/handlers_discussion.go

@@ -92,6 +92,8 @@ func DiscussionMessageCreateHandler(deps DiscussionDeps) http.HandlerFunc {
 		}
 		if errs.Body != "" {
 			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.Header().Set("HX-Retarget", "form[action$='/discussion/messages']")
+			w.Header().Set("HX-Reswap", "outerHTML")
 			w.WriteHeader(http.StatusUnprocessableEntity)
 			_ = templates.DiscussionComposer(tablo, form, errs, csrf.Token(r)).Render(r.Context(), w)
 			return
@@ -104,6 +106,8 @@ func DiscussionMessageCreateHandler(deps DiscussionDeps) http.HandlerFunc {
 		if err != nil {
 			slog.Default().Error("discussion create: CreateDiscussionMessage failed", "tablo_id", tablo.ID, "err", err)
 			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.Header().Set("HX-Retarget", "form[action$='/discussion/messages']")
+			w.Header().Set("HX-Reswap", "outerHTML")
 			w.WriteHeader(http.StatusInternalServerError)
 			errs.General = "Message could not be sent. Please try again."
 			_ = templates.DiscussionComposer(tablo, form, errs, csrf.Token(r)).Render(r.Context(), w)
@@ -118,11 +122,14 @@ func DiscussionMessageCreateHandler(deps DiscussionDeps) http.HandlerFunc {
 			http.Error(w, "internal server error", http.StatusInternalServerError)
 			return
 		}
-		message := templates.DiscussionMessageFromRow(row, row.AuthorUserID == user.ID)
+		message := templates.DiscussionMessageFromRow(row, user.ID)
 		data := templates.DiscussionTabData{Messages: []templates.DiscussionMessageView{message}}
 		markDiscussionRead(r, deps.Queries, tablo, user.ID, data)
 		if deps.Realtime != nil {
-			html, err := renderDiscussionMessageHTML(r, message)
+			// SSE recipients are never the author — always render as IsOwn: false.
+			sseMessage := message
+			sseMessage.IsOwn = false
+			html, err := renderDiscussionMessageHTML(r, sseMessage)
 			if err != nil {
 				slog.Default().Warn("discussion create: render realtime message failed", "tablo_id", tablo.ID, "message_id", msg.ID, "err", err)
 			} else {

backend/internal/web/ui/app.css

@@ -749,7 +749,7 @@
 }
 
 .message-row.message-own .message-bubble {
-  background-color: rgba(128, 78, 236, 0.10);
+  background-color: color-mix(in srgb, var(--color-brand-primary) 10%, transparent);
   border-radius: 0.75rem 0.75rem 0.25rem 0.75rem;
   color: var(--color-text-primary);
 }

backend/templates/discussion.templ

@@ -12,22 +12,20 @@ templ DiscussionTabFragment(tablo sqlc.Tablo, data DiscussionTabData, form Discu
 		<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>
-				<p class="mt-1 text-sm text-slate-600">1 participant</p>
 			</div>
 		</div>
 		<div id="discussion-messages" class="ui-card">
 			if len(data.Messages) == 0 {
 				@DiscussionEmptyState()
-			} else {
-				<div class="divide-y divide-slate-100">
-					for i, message := range data.Messages {
-						if DiscussionShowDaySeparator(data.Messages, i) {
-							@DiscussionDaySeparator(message.CreatedAt)
-						}
-						@DiscussionMessageRow(message)
-					}
-				</div>
 			}
+			<div id="discussion-message-list" class="divide-y divide-slate-100">
+				for i, message := range data.Messages {
+					if DiscussionShowDaySeparator(data.Messages, i) {
+						@DiscussionDaySeparator(message.CreatedAt)
+					}
+					@DiscussionMessageRow(message)
+				}
+			</div>
 		</div>
 		@DiscussionComposer(tablo, form, errs, csrfToken)
 	</div>
@@ -71,9 +69,8 @@ templ DiscussionComposer(tablo sqlc.Tablo, form DiscussionForm, errs DiscussionE
 		method="POST"
 		action={ templ.SafeURL(DiscussionPostURL(tablo.ID)) }
 		hx-post={ DiscussionPostURL(tablo.ID) }
-		hx-target="#discussion-messages"
+		hx-target="#discussion-message-list"
 		hx-swap="beforeend"
-		hx-on::after-request="if (event.detail.xhr.status >= 200 && event.detail.xhr.status < 300) this.reset()"
 		class="border-t border-slate-200 pt-4"
 	>
 		@ui.CSRFField(csrfToken)

backend/templates/discussion_forms.go

@@ -67,13 +67,13 @@ func DiscussionMessagesFromRows(rows []sqlc.ListDiscussionMessagesByTabloRow, cu
 	return messages
 }
 
-func DiscussionMessageFromRow(row sqlc.GetDiscussionMessageWithAuthorRow, isOwn bool) DiscussionMessageView {
+func DiscussionMessageFromRow(row sqlc.GetDiscussionMessageWithAuthorRow, currentUserID uuid.UUID) DiscussionMessageView {
 	return DiscussionMessageView{
 		ID:          row.ID,
 		AuthorEmail: row.AuthorEmail,
 		Body:        row.Body,
 		CreatedAt:   row.CreatedAt.Time,
-		IsOwn:       isOwn,
+		IsOwn:       row.AuthorUserID == currentUserID,
 	}
 }