feat(agent): implement agent execution engine and turn handling with background processing

apps/interfaces/daemon/src/handler.rs

@@ -292,6 +292,45 @@ fn handle_submit_input(state: &mut AppStateRest, text: String) {
     state.input.cursor = 0;
     state.input.history_idx = None;
     state.dirty = true;
+
+    // Resolve LLM provider credentials
+    let provider_name = &state.settings.provider;
+    let provider_cfg = state.app_config.providers.get(provider_name).cloned();
+    let mut api_key = String::new();
+    if let Some(key) = state.settings.api_keys.get(provider_name) {
+        api_key = key.clone();
+    } else if let Some(ref cfg) = provider_cfg {
+        if let Some(ref default_key) = cfg.default_api_key {
+            api_key = default_key.clone();
+        }
+        if api_key.is_empty() {
+            if let Some(ref env_name) = cfg.api_key_env {
+                if let Ok(val) = std::env::var(env_name) {
+                    api_key = val;
+                }
+            }
+        }
+    }
+
+    let messages = state
+        .session_runtime
+        .as_ref()
+        .map(|rt| rt.messages.clone())
+        .unwrap_or_default();
+
+    let params = zesdex_infrastructure::agent::AgentTurnParams {
+        messages,
+        session_dir: state.session_dir.clone(),
+        workspace_roots: state.workspace_roots.clone(),
+        turn_events: state.turn_events.clone(),
+        in_flight: std::sync::Arc::new(std::sync::atomic::AtomicBool::new(false)),
+        abort: state.abort_flag.clone(),
+        api_key,
+        model: state.settings.model.clone(),
+        api_base: provider_cfg.map(|cfg| cfg.api_base.clone()),
+    };
+
+    zesdex_infrastructure::agent::spawn_agent_turn(params);
 }
 
 fn handle_delete_char(state: &mut AppStateRest) {