feat: experimental menu (#8071)

This will automatically render any `Stage::Beta` features.

The change only gets applied to the *next session*. This started as a
bug but actually this is a good thing to prevent out of distribution
push

<img width="986" height="288" alt="Screenshot 2025-12-15 at 15 38 35"
src="https://github.com/user-attachments/assets/78b7a71d-0e43-4828-a118-91c5237909c7"
/>


<img width="509" height="109" alt="Screenshot 2025-12-15 at 17 35 44"
src="https://github.com/user-attachments/assets/6933de52-9b66-4abf-b58b-a5f26d5747e2"
/>

codex-rs/tui/src/chatwidget.rs

@@ -9,6 +9,8 @@ use codex_app_server_protocol::AuthMode;
 use codex_backend_client::Client as BackendClient;
 use codex_core::config::Config;
 use codex_core::config::types::Notifications;
+use codex_core::features::FEATURES;
+use codex_core::features::Feature;
 use codex_core::git_info::current_branch_name;
 use codex_core::git_info::local_git_branches;
 use codex_core::openai_models::model_family::ModelFamily;
@@ -85,9 +87,11 @@ use tracing::debug;
 use crate::app_event::AppEvent;
 use crate::app_event_sender::AppEventSender;
 use crate::bottom_pane::ApprovalRequest;
+use crate::bottom_pane::BetaFeatureItem;
 use crate::bottom_pane::BottomPane;
 use crate::bottom_pane::BottomPaneParams;
 use crate::bottom_pane::CancellationEvent;
+use crate::bottom_pane::ExperimentalFeaturesView;
 use crate::bottom_pane::InputResult;
 use crate::bottom_pane::SelectionAction;
 use crate::bottom_pane::SelectionItem;
@@ -1571,6 +1575,9 @@ impl ChatWidget {
             SlashCommand::Approvals => {
                 self.open_approvals_popup();
             }
+            SlashCommand::Experimental => {
+                self.open_experimental_popup();
+            }
             SlashCommand::Quit | SlashCommand::Exit => {
                 self.request_exit();
             }
@@ -2635,6 +2642,24 @@ impl ChatWidget {
         });
     }
 
+    pub(crate) fn open_experimental_popup(&mut self) {
+        let features: Vec<BetaFeatureItem> = FEATURES
+            .iter()
+            .filter_map(|spec| {
+                let description = spec.stage.beta_menu_description()?;
+                Some(BetaFeatureItem {
+                    feature: spec.id,
+                    name: feature_label_from_key(spec.key),
+                    description: description.to_string(),
+                    enabled: self.config.features.enabled(spec.id),
+                })
+            })
+            .collect();
+
+        let view = ExperimentalFeaturesView::new(features, self.app_event_tx.clone());
+        self.bottom_pane.show_view(Box::new(view));
+    }
+
     fn approval_preset_actions(
         approval: AskForApproval,
         sandbox: SandboxPolicy,
@@ -2977,6 +3002,14 @@ impl ChatWidget {
         }
     }
 
+    pub(crate) fn set_feature_enabled(&mut self, feature: Feature, enabled: bool) {
+        if enabled {
+            self.config.features.enable(feature);
+        } else {
+            self.config.features.disable(feature);
+        }
+    }
+
     pub(crate) fn set_full_access_warning_acknowledged(&mut self, acknowledged: bool) {
         self.config.notices.hide_full_access_warning = Some(acknowledged);
     }
@@ -3310,6 +3343,23 @@ impl ChatWidget {
     }
 }
 
+fn feature_label_from_key(key: &str) -> String {
+    let mut out = String::with_capacity(key.len());
+    let mut capitalize = true;
+    for ch in key.chars() {
+        if ch == '_' || ch == '-' {
+            out.push(' ');
+            capitalize = true;
+        } else if capitalize {
+            out.push(ch.to_ascii_uppercase());
+            capitalize = false;
+        } else {
+            out.push(ch);
+        }
+    }
+    out
+}
+
 impl Drop for ChatWidget {
     fn drop(&mut self) {
         self.stop_rate_limit_poller();