Branch conversations when editing earlier TUI prompts (#33201)

## What changed

- Fork the conversation immediately before the selected prompt instead of rolling back the current thread in place, preserving the original conversation.
- Reopen the selected prompt in the new conversation with its images, text elements, and mention bindings intact.
- Start a fresh conversation when editing the first prompt, show a dedicated continuation notice, and restore the prompt with an error if branching fails.

## Testing

- Cover branching before first and later prompts, source preservation, prompt restoration, hidden review prompts, mid-turn steering, in-progress turns, stale transcript entries, and mention bindings.

GitOrigin-RevId: 15473535b3f9733b0300711a498969e6d389db79

codex-rs/tui/src/chatwidget.rs

@@ -163,8 +163,6 @@ use codex_terminal_detection::terminal_info;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_cli::resume_hint;
 use codex_utils_path_uri::PathUri;
-use codex_utils_plugins::mention_syntax::PLUGIN_TEXT_MENTION_SIGIL;
-use codex_utils_plugins::mention_syntax::TOOL_MENTION_SIGIL;
 use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;
 use crossterm::event::KeyEventKind;
@@ -436,6 +434,7 @@ use self::user_messages::UserMessageHistoryOverride;
 use self::user_messages::UserMessageHistoryRecord;
 use self::user_messages::app_server_text_elements;
 pub(crate) use self::user_messages::create_initial_user_message;
+pub(crate) use self::user_messages::mention_bindings_from_user_inputs;
 use self::user_messages::merge_user_messages;
 use self::user_messages::merge_user_messages_with_history_record;
 #[cfg(test)]
@@ -796,6 +795,7 @@ pub(crate) enum ReplayKind {
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum SessionConfiguredDisplay {
     Normal,
+    PromptEdit,
     /// Apply session state without emitting the session info cell.
     Quiet,
     SideConversation,
@@ -1262,69 +1262,13 @@ impl ChatWidget {
             if self.review.is_review_mode {
                 return;
             }
-            let message = display.message.as_str();
-            let mention_start = |sigil: char, mention: &str| {
-                let token = format!("{sigil}{mention}");
-                message.match_indices(&token).find_map(|(start, _)| {
-                    let end = start + token.len();
-                    message
-                        .as_bytes()
-                        .get(end)
-                        .is_none_or(|byte| {
-                            !byte.is_ascii_alphanumeric() && !matches!(byte, b'_' | b'-')
-                        })
-                        .then_some(start)
-                })
-            };
-            let mut mention_bindings: Vec<MentionBinding> = items
-                .iter()
-                .filter_map(|item| match item {
-                    UserInput::Skill { name, path } => Some(MentionBinding {
-                        sigil: TOOL_MENTION_SIGIL,
-                        mention: name.clone(),
-                        path: path.to_string_lossy().into_owned(),
-                    }),
-                    UserInput::Mention { name, path } => {
-                        let plugin_id = path.strip_prefix("plugin://");
-                        let mention = if let Some(plugin_id) = plugin_id {
-                            plugin_id
-                                .split_once('@')
-                                .map(|(plugin_name, _)| plugin_name)
-                                .unwrap_or(plugin_id)
-                                .to_string()
-                        } else if path.starts_with("app://") {
-                            codex_connectors::metadata::connector_mention_slug_from_name(name)
-                        } else {
-                            name.clone()
-                        };
-                        let sigil = if plugin_id.is_some()
-                            && mention_start(PLUGIN_TEXT_MENTION_SIGIL, &mention).is_some()
-                        {
-                            PLUGIN_TEXT_MENTION_SIGIL
-                        } else {
-                            TOOL_MENTION_SIGIL
-                        };
-                        Some(MentionBinding {
-                            sigil,
-                            mention,
-                            path: path.clone(),
-                        })
-                    }
-                    UserInput::Text { .. }
-                    | UserInput::Image { .. }
-                    | UserInput::LocalImage { .. } => None,
-                })
-                .collect();
-            mention_bindings.sort_by_key(|binding| {
-                mention_start(binding.sigil, &binding.mention).unwrap_or(usize::MAX)
-            });
             self.bottom_pane
                 .record_replayed_user_message_history(HistoryEntry {
                     text: display.message.clone(),
                     text_elements: display.text_elements.clone(),
                     local_image_paths: display.local_images.clone(),
                     remote_image_urls: display.remote_image_urls.clone(),
-                    mention_bindings,
+                    mention_bindings: mention_bindings_from_user_inputs(items, &display.message),
                     pending_pastes: Vec::new(),
                 });
             self.on_user_message_display(display);
@@ -1745,18 +1689,6 @@ impl ChatWidget {
         self.bottom_pane.insert_str(text);
     }
 
-    /// Replace the composer content with the provided text and reset cursor.
-    pub(crate) fn set_composer_text(
-        &mut self,
-        text: String,
-        text_elements: Vec<TextElement>,
-        local_image_paths: Vec<PathBuf>,
-    ) {
-        self.bottom_pane
-            .set_composer_text(text, text_elements, local_image_paths);
-        self.refresh_plan_mode_nudge();
-    }
-
     pub(crate) fn set_remote_image_urls(&mut self, remote_image_urls: Vec<String>) {
         self.bottom_pane.set_remote_image_urls(remote_image_urls);
     }