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/chat.rs

@@ -30,8 +30,14 @@ pub struct ChatMessage {
     pub text: String,
     /// Pre-formatted UTC wall-clock time, e.g. "14:03:27".
     pub time: String,
+    /// Publish instant as UTC epoch milliseconds; orders history.
+    #[serde(default)]
+    pub ts: i64,
 }
 
+/// How many messages `room_history` backfills when joining a room.
+pub const HISTORY_LIMIT: i64 = 100;
+
 /// Publishes a message to the room's NATS subject. Requires a signed-in
 /// session; the sender identity always comes from the session, never from
 /// the client.
@@ -58,13 +64,15 @@ pub async fn send_message(room: String, text: String) -> Result<(), ServerFnErro
     };
 
     let state = expect_context::<AppState>();
+    let now = chrono::Utc::now();
     let msg = ChatMessage {
         id: uuid::Uuid::new_v4().to_string(),
         room: room.clone(),
         username: user.username,
         display_name: user.display_name,
         text,
-        time: chrono::Utc::now().format("%H:%M:%S").to_string(),
+        time: now.format("%H:%M:%S").to_string(),
+        ts: now.timestamp_millis(),
     };
     let payload = serde_json::to_vec(&msg).map_err(|e| ServerFnError::new(e.to_string()))?;
     state
@@ -74,3 +82,29 @@ pub async fn send_message(room: String, text: String) -> Result<(), ServerFnErro
         .map_err(|e| ServerFnError::new(format!("nats publish failed: {e}")))?;
     Ok(())
 }
+
+/// Returns the most recent messages for a room (oldest first), read from the
+/// Postgres archive maintained by the JetStream consumer.
+#[server]
+pub async fn room_history(room: String) -> Result<Vec<ChatMessage>, ServerFnError> {
+    use crate::auth::{User, SESSION_USER_KEY};
+    use crate::server::AppState;
+
+    if !is_valid_room(&room) {
+        return Err(ServerFnError::new("unknown room"));
+    }
+    let session: tower_sessions::Session = leptos_axum::extract().await?;
+    if session
+        .get::<User>(SESSION_USER_KEY)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?
+        .is_none()
+    {
+        return Err(ServerFnError::new("not signed in"));
+    }
+
+    let state = expect_context::<AppState>();
+    crate::server::store::recent(&state.pool, &room, HISTORY_LIMIT)
+        .await
+        .map_err(|e| ServerFnError::new(format!("history unavailable: {e}")))
+}