Fix infinite scroll by switching from revealed to intersect trigger

HTMX's revealed trigger listens for window.scroll events, which never
fire when scrolling inside .message-list (overflow-y: auto). The
intersect trigger uses IntersectionObserver which correctly handles
overflow clipping in ancestor scroll containers.

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

Author: emilhauk

internal/browser/realtime_test.go

@@ -155,13 +155,13 @@ func TestNoDuplicates_Scrollback(t *testing.T) {
 	page.Timeout(3 * time.Second).MustElement(".scroll-sentinel")
 
 	// Trigger the sentinel directly via htmx.trigger so we don't depend on
-	// HTMX's polling interval detecting the element in the headless viewport.
-	// This dispatches the same 'revealed' DOM event that HTMX fires internally
-	// when its setInterval determines the element is scrolled into view — the
-	// full hx-get / hx-swap="beforebegin" path is exercised identically.
+	// the IntersectionObserver firing in the headless viewport. This dispatches
+	// the same 'intersect' event that HTMX fires internally when its observer
+	// detects the element — the full hx-get / hx-swap="beforebegin" path is
+	// exercised identically.
 	page.MustEval(`() => {
 		const s = document.querySelector('.scroll-sentinel');
-		if (s) htmx.trigger(s, 'revealed');
+		if (s) htmx.trigger(s, 'intersect');
 	}`)
 
 	// Poll until all 55 articles are present (up to 8 s).

web/templates/history.html

@@ -3,7 +3,7 @@
 {{if .Data.HasMore}}
 <div class="scroll-sentinel"
      hx-get="/rooms/{{.Data.RoomID}}/messages?before={{.Data.OldestMS}}&limit=50"
-     hx-trigger="revealed"
+     hx-trigger="intersect once"
      hx-swap="beforebegin"></div>
 {{end}}
 

web/templates/room.html

@@ -154,7 +154,7 @@ <h1 class="room-main__title"># {{.Data.Room.Name}}</h1>
         {{if .Data.OldestMS}}
         <div class="scroll-sentinel"
              hx-get="/rooms/{{.Data.Room.ID}}/messages?before={{.Data.OldestMS}}&limit=50"
-             hx-trigger="revealed"
+             hx-trigger="intersect once"
              hx-swap="beforebegin"></div>
         {{end}}