TUI: collaboration mode UX + always submit UserTurn when enabled (#9461)

- Adds experimental collaboration modes UX in TUI: Plan / Pair
Programming / Execute.
- Gated behind `Feature::CollaborationModes`; existing behavior remains
unchanged when disabled.
- Selection UX:
- `Shift+Tab` cycles modes while idle (no task running, no modal/popup).
- `/collab` cycles; `/collab <plan|pair|pp|execute|exec>` sets
explicitly.
- Footer flash after changes + shortcut overlay shows `Shift+Tab` “to
change mode”.
  - `/status` shows “Collaboration mode”.
- Submission semantics:
- When enabled: every submit uses `Op::UserTurn` and always includes
`collaboration_mode: Some(...)` (default Pair Programming).
  - Removes the one-shot “pending collaboration mode” behavior.
- Implementation:
- New `tui/src/collaboration_modes.rs` (selection enum/cycle, `/collab`
parsing, resolve to `CollaborationMode`, footer flash line).
- Fallback: `resolve_mode_or_fallback` synthesizes a `CollaborationMode`
when presets are missing (uses current model + reasoning effort; no
`developer_instructions`) to avoid core falling back to `Custom`.
  - TODO: migrate TUI to use `Op::UserTurn`.

codex-rs/tui/src/bottom_pane/command_popup.rs

@@ -37,13 +37,20 @@ pub(crate) struct CommandPopup {
     state: ScrollState,
 }
 
+#[derive(Clone, Copy, Debug, Default)]
+pub(crate) struct CommandPopupFlags {
+    pub(crate) skills_enabled: bool,
+    pub(crate) collaboration_modes_enabled: bool,
+}
+
 impl CommandPopup {
-    pub(crate) fn new(mut prompts: Vec<CustomPrompt>, skills_enabled: bool) -> Self {
+    pub(crate) fn new(mut prompts: Vec<CustomPrompt>, flags: CommandPopupFlags) -> Self {
         let allow_elevate_sandbox = windows_degraded_sandbox_active();
         let builtins: Vec<(&'static str, SlashCommand)> = built_in_slash_commands()
             .into_iter()
-            .filter(|(_, cmd)| skills_enabled || *cmd != SlashCommand::Skills)
+            .filter(|(_, cmd)| flags.skills_enabled || *cmd != SlashCommand::Skills)
             .filter(|(_, cmd)| allow_elevate_sandbox || *cmd != SlashCommand::ElevateSandbox)
+            .filter(|(_, cmd)| flags.collaboration_modes_enabled || *cmd != SlashCommand::Collab)
             .collect();
         // Exclude prompts that collide with builtin command names and sort by name.
         let exclude: HashSet<String> = builtins.iter().map(|(n, _)| (*n).to_string()).collect();
@@ -231,7 +238,7 @@ mod tests {
 
     #[test]
     fn filter_includes_init_when_typing_prefix() {
-        let mut popup = CommandPopup::new(Vec::new(), false);
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
         // Simulate the composer line starting with '/in' so the popup filters
         // matching commands by prefix.
         popup.on_composer_text_change("/in".to_string());
@@ -251,7 +258,7 @@ mod tests {
 
     #[test]
     fn selecting_init_by_exact_match() {
-        let mut popup = CommandPopup::new(Vec::new(), false);
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
         popup.on_composer_text_change("/init".to_string());
 
         // When an exact match exists, the selected command should be that
@@ -266,7 +273,7 @@ mod tests {
 
     #[test]
     fn model_is_first_suggestion_for_mo() {
-        let mut popup = CommandPopup::new(Vec::new(), false);
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
         popup.on_composer_text_change("/mo".to_string());
         let matches = popup.filtered_items();
         match matches.first() {
@@ -280,7 +287,7 @@ mod tests {
 
     #[test]
     fn filtered_commands_keep_presentation_order() {
-        let mut popup = CommandPopup::new(Vec::new(), false);
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
         popup.on_composer_text_change("/m".to_string());
 
         let cmds: Vec<&str> = popup
@@ -322,7 +329,7 @@ mod tests {
                 argument_hint: None,
             },
         ];
-        let popup = CommandPopup::new(prompts, false);
+        let popup = CommandPopup::new(prompts, CommandPopupFlags::default());
         let items = popup.filtered_items();
         let mut prompt_names: Vec<String> = items
             .into_iter()
@@ -346,7 +353,7 @@ mod tests {
                 description: None,
                 argument_hint: None,
             }],
-            false,
+            CommandPopupFlags::default(),
         );
         let items = popup.filtered_items();
         let has_collision_prompt = items.into_iter().any(|it| match it {
@@ -369,7 +376,7 @@ mod tests {
                 description: Some("Create feature branch, commit and open draft PR.".to_string()),
                 argument_hint: None,
             }],
-            false,
+            CommandPopupFlags::default(),
         );
         let rows = popup.rows_from_matches(vec![(CommandItem::UserPrompt(0), None, 0)]);
         let description = rows.first().and_then(|row| row.description.as_deref());
@@ -389,7 +396,7 @@ mod tests {
                 description: None,
                 argument_hint: None,
             }],
-            false,
+            CommandPopupFlags::default(),
         );
         let rows = popup.rows_from_matches(vec![(CommandItem::UserPrompt(0), None, 0)]);
         let description = rows.first().and_then(|row| row.description.as_deref());
@@ -398,7 +405,7 @@ mod tests {
 
     #[test]
     fn fuzzy_filter_matches_subsequence_for_ac() {
-        let mut popup = CommandPopup::new(Vec::new(), false);
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
         popup.on_composer_text_change("/ac".to_string());
 
         let cmds: Vec<&str> = popup
@@ -414,4 +421,40 @@ mod tests {
             "expected fuzzy search for '/ac' to include compact and feedback, got {cmds:?}"
         );
     }
+
+    #[test]
+    fn collab_command_hidden_when_collaboration_modes_disabled() {
+        let mut popup = CommandPopup::new(Vec::new(), CommandPopupFlags::default());
+        popup.on_composer_text_change("/coll".to_string());
+
+        let cmds: Vec<&str> = popup
+            .filtered_items()
+            .into_iter()
+            .filter_map(|item| match item {
+                CommandItem::Builtin(cmd) => Some(cmd.command()),
+                CommandItem::UserPrompt(_) => None,
+            })
+            .collect();
+        assert!(
+            !cmds.contains(&"collab"),
+            "expected '/collab' to be hidden when collaboration modes are disabled, got {cmds:?}"
+        );
+    }
+
+    #[test]
+    fn collab_command_visible_when_collaboration_modes_enabled() {
+        let mut popup = CommandPopup::new(
+            Vec::new(),
+            CommandPopupFlags {
+                skills_enabled: false,
+                collaboration_modes_enabled: true,
+            },
+        );
+        popup.on_composer_text_change("/collab".to_string());
+
+        match popup.selected_item() {
+            Some(CommandItem::Builtin(cmd)) => assert_eq!(cmd.command(), "collab"),
+            other => panic!("expected collab to be selected for exact match, got {other:?}"),
+        }
+    }
 }