feat: better session creation handling

src/app/generation.rs

@@ -51,7 +51,7 @@ impl From<StoredMessage> for ChatMessage {
 
 impl App {
     pub(super) fn start_generation(&mut self) {
-        if self.generating || self.selected_session.is_none() {
+        if self.generating || self.selected_project.is_none() {
             return;
         }
         let prompt = self.composer.trim().to_owned();
@@ -78,9 +78,6 @@ impl App {
             }
         };
         let assistant_reasoning = effective.turn.reasoning_mode != ReasoningMode::Direct;
-        let session_id = self
-            .selected_session
-            .expect("a selected session was checked");
         #[cfg(target_os = "macos")]
         let mut messages = self
             .conversation
@@ -104,6 +101,22 @@ impl App {
 
         #[cfg(target_os = "macos")]
         {
+            // A draft session only reaches the database once there is a turn to store.
+            let session_id = match self.selected_session {
+                Some(session_id) => session_id,
+                None => {
+                    let Some(project_id) = self.selected_project else {
+                        return;
+                    };
+                    match self.persist_session(project_id) {
+                        Ok(session_id) => session_id,
+                        Err(error) => {
+                            self.error = Some(format!("Could not create the session: {error}"));
+                            return;
+                        }
+                    }
+                }
+            };
             let Some(service) = &self.generation_service else {
                 self.error = Some("The model runtime is unavailable.".into());
                 return;