fix: ensure the first user message always displays after the session info (#988)

Previously, if the first user message was sent with the command
invocation, e.g.:

```
$ cargo run --bin codex 'hello'
```

Then the user message was added as the first entry in the history and
then `is_first_event` would be `false` here:


031df77dfb/codex-rs/tui/src/conversation_history_widget.rs (L178-L179)

which would prevent the "welcome" message with things like the the model
version from displaying.

The fix in this PR is twofold:

* Reorganize the logic so the `ChatWidget` constructor stores
`initial_user_message` rather than sending it right away. Now inside
`handle_codex_event()`, it waits for the `SessionConfigured` event and
sends the `initial_user_message`, if it exists.
* In `conversation_history_widget.rs`, `add_session_info()` checks to
see whether a `WelcomeMessage` exists in the history when determining
the value of `has_welcome_message`. By construction, we expect that
`WelcomeMessage` is always the first message (in which case the existing
`let is_first_event = self.entries.is_empty();` logic would be sound),
but we decide to be extra defensive in case an `EventMsg::Error` is
processed before `EventMsg::SessionConfigured`.

codex-rs/tui/src/chatwidget.rs

@@ -44,6 +44,7 @@ pub(crate) struct ChatWidget<'a> {
     bottom_pane: BottomPane<'a>,
     input_focus: InputFocus,
     config: Config,
+    initial_user_message: Option<UserMessage>,
 }
 
 #[derive(Clone, Copy, Eq, PartialEq)]
@@ -52,6 +53,28 @@ enum InputFocus {
     BottomPane,
 }
 
+struct UserMessage {
+    text: String,
+    image_paths: Vec<PathBuf>,
+}
+
+impl From<String> for UserMessage {
+    fn from(text: String) -> Self {
+        Self {
+            text,
+            image_paths: Vec::new(),
+        }
+    }
+}
+
+fn create_initial_user_message(text: String, image_paths: Vec<PathBuf>) -> Option<UserMessage> {
+    if text.is_empty() && image_paths.is_empty() {
+        None
+    } else {
+        Some(UserMessage { text, image_paths })
+    }
+}
+
 impl ChatWidget<'_> {
     pub(crate) fn new(
         config: Config,
@@ -93,7 +116,7 @@ impl ChatWidget<'_> {
             }
         });
 
-        let mut chat_widget = Self {
+        Self {
             app_event_tx: app_event_tx.clone(),
             codex_op_tx,
             conversation_history: ConversationHistoryWidget::new(),
@@ -103,14 +126,11 @@ impl ChatWidget<'_> {
             }),
             input_focus: InputFocus::BottomPane,
             config,
-        };
-
-        if initial_prompt.is_some() || !initial_images.is_empty() {
-            let text = initial_prompt.unwrap_or_default();
-            chat_widget.submit_user_message_with_images(text, initial_images);
+            initial_user_message: create_initial_user_message(
+                initial_prompt.unwrap_or_default(),
+                initial_images,
+            ),
         }
-
-        chat_widget
     }
 
     pub(crate) fn handle_key_event(&mut self, key_event: KeyEvent) {
@@ -141,19 +161,15 @@ impl ChatWidget<'_> {
             }
             InputFocus::BottomPane => match self.bottom_pane.handle_key_event(key_event) {
                 InputResult::Submitted(text) => {
-                    self.submit_user_message(text);
+                    self.submit_user_message(text.into());
                 }
                 InputResult::None => {}
             },
         }
     }
 
-    fn submit_user_message(&mut self, text: String) {
-        // Forward to codex and update conversation history.
-        self.submit_user_message_with_images(text, vec![]);
-    }
-
-    fn submit_user_message_with_images(&mut self, text: String, image_paths: Vec<PathBuf>) {
+    fn submit_user_message(&mut self, user_message: UserMessage) {
+        let UserMessage { text, image_paths } = user_message;
         let mut items: Vec<InputItem> = Vec::new();
 
         if !text.is_empty() {
@@ -207,6 +223,13 @@ impl ChatWidget<'_> {
                 // composer can navigate through past messages.
                 self.bottom_pane
                     .set_history_metadata(event.history_log_id, event.history_entry_count);
+
+                if let Some(user_message) = self.initial_user_message.take() {
+                    // If the user provided an initial message, add it to the
+                    // conversation history.
+                    self.submit_user_message(user_message);
+                }
+
                 self.request_redraw();
             }
             EventMsg::AgentMessage(AgentMessageEvent { message }) => {

codex-rs/tui/src/conversation_history_widget.rs

@@ -175,8 +175,18 @@ impl ConversationHistoryWidget {
     /// Note `model` could differ from `config.model` if the agent decided to
     /// use a different model than the one requested by the user.
     pub fn add_session_info(&mut self, config: &Config, event: SessionConfiguredEvent) {
-        let is_first_event = self.entries.is_empty();
-        self.add_to_history(HistoryCell::new_session_info(config, event, is_first_event));
+        // In practice, SessionConfiguredEvent should always be the first entry
+        // in the history, but it is possible that an error could be sent
+        // before the session info.
+        let has_welcome_message = self
+            .entries
+            .iter()
+            .any(|entry| matches!(entry.cell, HistoryCell::WelcomeMessage { .. }));
+        self.add_to_history(HistoryCell::new_session_info(
+            config,
+            event,
+            !has_welcome_message,
+        ));
     }
 
     pub fn add_user_message(&mut self, message: String) {