Persist chat history to Postgres via durable JetStream consumer

DATABASE_URL required at startup; schema self-initializes.
Compose gains a postgres service for standalone dev.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app.rs

@@ -8,6 +8,8 @@ use leptos_router::{
 
 use crate::auth::{current_user, User};
 use crate::chat::{is_valid_room, room_subject, ChatMessage, SendMessage, DEFAULT_ROOM, ROOMS};
+#[cfg(feature = "hydrate")]
+use crate::chat::room_history;
 
 pub fn shell(options: LeptosOptions) -> impl IntoView {
     view! {
@@ -144,7 +146,7 @@ fn ChatShell(room: Memo<String>, user: User) -> impl IntoView {
     {
         let es_handle = StoredValue::new_local(None::<web_sys::EventSource>);
         Effect::new(move |_| {
-            let room = room.get();
+            let room_name = room.get();
             es_handle.update_value(|es| {
                 if let Some(es) = es.take() {
                     es.close();
@@ -152,7 +154,28 @@ fn ChatShell(room: Memo<String>, user: User) -> impl IntoView {
             });
             messages.set(Vec::new());
             status.set(BusStatus::Connecting);
-            es_handle.set_value(open_event_source(&room, messages, status));
+            es_handle.set_value(open_event_source(&room_name, messages, status));
+
+            // Backfill from the Postgres archive; live SSE messages may land
+            // first, so merge by id (history first, then unseen live ones).
+            leptos::task::spawn_local(async move {
+                let Ok(history) = room_history(room_name.clone()).await else {
+                    return;
+                };
+                // The user may have switched rooms while we were fetching.
+                if room.get_untracked() != room_name {
+                    return;
+                }
+                messages.update(|live| {
+                    let mut merged = history;
+                    for m in live.drain(..) {
+                        if !merged.iter().any(|h| h.id == m.id) {
+                            merged.push(m);
+                        }
+                    }
+                    *live = merged;
+                });
+            });
         });
         on_cleanup(move || {
             es_handle.update_value(|es| {