add chat function

#

src/state.rs

@@ -0,0 +1,32 @@
+use dashmap::DashMap;
+use tokio::sync::broadcast;
+use crate::models::ChatSession;
+
+pub struct AppState {
+    pub sessions: DashMap<String, ChatSession>,
+    // broadcast channel: session_id -> sender
+    pub notifiers: DashMap<String, broadcast::Sender<String>>,
+    // agent broadcast for new sessions
+    pub agent_notifier: broadcast::Sender<String>,
+}
+
+impl AppState {
+    pub fn new() -> Self {
+        let (agent_tx, _) = broadcast::channel(64);
+        Self {
+            sessions: DashMap::new(),
+            notifiers: DashMap::new(),
+            agent_notifier: agent_tx,
+        }
+    }
+
+    pub fn get_or_create_notifier(&self, session_id: &str) -> broadcast::Sender<String> {
+        if let Some(tx) = self.notifiers.get(session_id) {
+            tx.clone()
+        } else {
+            let (tx, _) = broadcast::channel(64);
+            self.notifiers.insert(session_id.to_string(), tx.clone());
+            tx
+        }
+    }
+}