diff --git a/crates/gpui3/src/app.rs b/crates/gpui3/src/app.rs
index a6f83a6fc77303f03dbeea2387f95c2045ca2c22..d27fc6a3f6f6a1d9313bd423d33fab1d19eba251 100644
--- a/crates/gpui3/src/app.rs
+++ b/crates/gpui3/src/app.rs
@@ -14,19 +14,19 @@ use crate::{
 };
 use anyhow::{anyhow, Result};
 use collections::{HashMap, VecDeque};
-use futures::{future, Future};
+use futures::Future;
 use parking_lot::Mutex;
 use slotmap::SlotMap;
 use smallvec::SmallVec;
 use std::{
     any::{type_name, Any, TypeId},
-    marker::PhantomData,
+    mem,
     sync::{Arc, Weak},
 };
 use util::ResultExt;
 
 #[derive(Clone)]
-pub struct App(Arc<Mutex<AppContext<MainThread>>>);
+pub struct App(Arc<Mutex<MainThread<AppContext>>>);
 
 impl App {
     pub fn production() -> Self {
@@ -44,8 +44,7 @@ impl App {
         let entities = EntityMap::new();
         let unit_entity = entities.redeem(entities.reserve(), ());
         Self(Arc::new_cyclic(|this| {
-            Mutex::new(AppContext {
-                thread: PhantomData,
+            Mutex::new(MainThread::new(AppContext {
                 this: this.clone(),
                 platform: MainThreadOnly::new(platform, dispatcher.clone()),
                 dispatcher,
@@ -59,13 +58,13 @@ impl App {
                 pending_effects: Default::default(),
                 observers: Default::default(),
                 layout_id_buffer: Default::default(),
-            })
+            }))
         }))
     }
 
     pub fn run<F>(self, on_finish_launching: F)
     where
-        F: 'static + FnOnce(&mut AppContext<MainThread>),
+        F: 'static + FnOnce(&mut MainThread<AppContext>),
     {
         let this = self.clone();
         let platform = self.0.lock().platform.clone();
@@ -76,12 +75,10 @@ impl App {
     }
 }
 
-type Handlers<Thread> =
-    SmallVec<[Arc<dyn Fn(&mut AppContext<Thread>) -> bool + Send + Sync + 'static>; 2]>;
+type Handlers = SmallVec<[Arc<dyn Fn(&mut AppContext) -> bool + Send + Sync + 'static>; 2]>;
 
-pub struct AppContext<Thread = ()> {
-    thread: PhantomData<Thread>,
-    this: Weak<Mutex<AppContext<Thread>>>,
+pub struct AppContext {
+    this: Weak<Mutex<MainThread<AppContext>>>,
     platform: MainThreadOnly<dyn Platform>,
     dispatcher: Arc<dyn PlatformDispatcher>,
     text_system: Arc<TextSystem>,
@@ -92,39 +89,89 @@ pub struct AppContext<Thread = ()> {
     pub(crate) entities: EntityMap,
     pub(crate) windows: SlotMap<WindowId, Option<Window>>,
     pub(crate) pending_effects: VecDeque<Effect>,
-    pub(crate) observers: HashMap<EntityId, Handlers<Thread>>,
+    pub(crate) observers: HashMap<EntityId, Handlers>,
     pub(crate) layout_id_buffer: Vec<LayoutId>, // We recycle this memory across layout requests.
 }
 
-impl<Thread: 'static + Send + Sync> AppContext<Thread> {
-    // TODO: Better names for these?
-    #[inline]
-    pub fn downcast(&self) -> &AppContext<()> {
-        // Any `Thread` can become `()`.
-        //
-        // Can't do this in a blanket `Deref` impl, as it infinitely recurses.
-        unsafe { std::mem::transmute::<&AppContext<Thread>, &AppContext<()>>(self) }
+impl AppContext {
+    fn update<R>(&mut self, update: impl FnOnce(&mut Self) -> R) -> R {
+        self.pending_updates += 1;
+        let result = update(self);
+        if self.pending_updates == 1 {
+            self.flush_effects();
+        }
+        self.pending_updates -= 1;
+        result
     }
 
-    #[inline]
-    pub fn downcast_mut(&mut self) -> &mut AppContext<()> {
-        // Any `Thread` can become `()`.
-        //
-        // Can't do this in a blanket `DerefMut` impl, as it infinitely recurses.
-        unsafe { std::mem::transmute::<&mut AppContext<Thread>, &mut AppContext<()>>(self) }
+    pub(crate) fn update_window<R>(
+        &mut self,
+        id: WindowId,
+        update: impl FnOnce(&mut WindowContext) -> R,
+    ) -> Result<R> {
+        self.update(|cx| {
+            let mut window = cx
+                .windows
+                .get_mut(id)
+                .ok_or_else(|| anyhow!("window not found"))?
+                .take()
+                .unwrap();
+
+            let result = update(&mut WindowContext::mutable(cx, &mut window));
+
+            cx.windows
+                .get_mut(id)
+                .ok_or_else(|| anyhow!("window not found"))?
+                .replace(window);
+
+            Ok(result)
+        })
     }
 
-    pub fn text_system(&self) -> &Arc<TextSystem> {
-        &self.text_system
+    fn flush_effects(&mut self) {
+        while let Some(effect) = self.pending_effects.pop_front() {
+            match effect {
+                Effect::Notify(entity_id) => self.apply_notify_effect(entity_id),
+            }
+        }
+
+        let dirty_window_ids = self
+            .windows
+            .iter()
+            .filter_map(|(window_id, window)| {
+                let window = window.as_ref().unwrap();
+                if window.dirty {
+                    Some(window_id)
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>();
+
+        for dirty_window_id in dirty_window_ids {
+            self.update_window(dirty_window_id, |cx| cx.draw())
+                .unwrap()
+                .log_err();
+        }
+    }
+
+    fn apply_notify_effect(&mut self, updated_entity: EntityId) {
+        if let Some(mut handlers) = self.observers.remove(&updated_entity) {
+            handlers.retain(|handler| handler(self));
+            if let Some(new_handlers) = self.observers.remove(&updated_entity) {
+                handlers.extend(new_handlers);
+            }
+            self.observers.insert(updated_entity, handlers);
+        }
     }
 
-    pub fn to_async(&self) -> AsyncContext<Thread> {
-        AsyncContext(self.this.clone())
+    pub fn to_async(&self) -> AsyncContext {
+        AsyncContext(unsafe { mem::transmute(self.this.clone()) })
     }
 
     pub fn run_on_main<R>(
         &self,
-        f: impl FnOnce(&mut AppContext<MainThread>) -> R + Send + 'static,
+        f: impl FnOnce(&mut MainThread<AppContext>) -> R + Send + 'static,
     ) -> impl Future<Output = R>
     where
         R: Send + 'static,
@@ -132,16 +179,15 @@ impl<Thread: 'static + Send + Sync> AppContext<Thread> {
         let this = self.this.upgrade().unwrap();
         run_on_main(self.dispatcher.clone(), move || {
             let cx = &mut *this.lock();
-            let main_thread_cx = unsafe {
-                std::mem::transmute::<&mut AppContext<Thread>, &mut AppContext<MainThread>>(cx)
-            };
-            main_thread_cx.update(|cx| f(cx))
+            cx.update(|cx| {
+                f(unsafe { mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx) })
+            })
         })
     }
 
     pub fn spawn_on_main<F, R>(
         &self,
-        f: impl FnOnce(&mut AppContext<MainThread>) -> F + Send + 'static,
+        f: impl FnOnce(&mut MainThread<AppContext>) -> F + Send + 'static,
     ) -> impl Future<Output = R>
     where
         F: Future<Output = R> + 'static,
@@ -150,13 +196,16 @@ impl<Thread: 'static + Send + Sync> AppContext<Thread> {
         let this = self.this.upgrade().unwrap();
         spawn_on_main(self.dispatcher.clone(), move || {
             let cx = &mut *this.lock();
-            let main_thread_cx = unsafe {
-                std::mem::transmute::<&mut AppContext<Thread>, &mut AppContext<MainThread>>(cx)
-            };
-            main_thread_cx.update(|cx| f(cx))
+            cx.update(|cx| {
+                f(unsafe { mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx) })
+            })
         })
     }
 
+    pub fn text_system(&self) -> &Arc<TextSystem> {
+        &self.text_system
+    }
+
     pub fn text_style(&self) -> TextStyle {
         let mut style = TextStyle::default();
         for refinement in &self.text_style_stack {
@@ -204,77 +253,6 @@ impl<Thread: 'static + Send + Sync> AppContext<Thread> {
             .and_then(|stack| stack.pop())
             .expect("state stack underflow");
     }
-
-    pub(crate) fn update_window<R>(
-        &mut self,
-        id: WindowId,
-        update: impl FnOnce(&mut WindowContext) -> R,
-    ) -> Result<R> {
-        self.update(|cx| {
-            let mut window = cx
-                .windows
-                .get_mut(id)
-                .ok_or_else(|| anyhow!("window not found"))?
-                .take()
-                .unwrap();
-
-            let result = update(&mut WindowContext::mutable(cx.downcast_mut(), &mut window));
-
-            cx.windows
-                .get_mut(id)
-                .ok_or_else(|| anyhow!("window not found"))?
-                .replace(window);
-
-            Ok(result)
-        })
-    }
-
-    fn update<R>(&mut self, update: impl FnOnce(&mut Self) -> R) -> R {
-        self.pending_updates += 1;
-        let result = update(self);
-        if self.pending_updates == 1 {
-            self.flush_effects();
-        }
-        self.pending_updates -= 1;
-        result
-    }
-
-    fn flush_effects(&mut self) {
-        while let Some(effect) = self.pending_effects.pop_front() {
-            match effect {
-                Effect::Notify(entity_id) => self.apply_notify_effect(entity_id),
-            }
-        }
-
-        let dirty_window_ids = self
-            .windows
-            .iter()
-            .filter_map(|(window_id, window)| {
-                let window = window.as_ref().unwrap();
-                if window.dirty {
-                    Some(window_id)
-                } else {
-                    None
-                }
-            })
-            .collect::<Vec<_>>();
-
-        for dirty_window_id in dirty_window_ids {
-            self.update_window(dirty_window_id, |cx| cx.draw())
-                .unwrap()
-                .log_err();
-        }
-    }
-
-    fn apply_notify_effect(&mut self, updated_entity: EntityId) {
-        if let Some(mut handlers) = self.observers.remove(&updated_entity) {
-            handlers.retain(|handler| handler(self));
-            if let Some(new_handlers) = self.observers.remove(&updated_entity) {
-                handlers.extend(new_handlers);
-            }
-            self.observers.insert(updated_entity, handlers);
-        }
-    }
 }
 
 impl Context for AppContext {
@@ -302,7 +280,15 @@ impl Context for AppContext {
     }
 }
 
-impl AppContext<MainThread> {
+impl MainThread<AppContext> {
+    fn update<R>(&mut self, update: impl FnOnce(&mut Self) -> R) -> R {
+        self.0.update(|cx| {
+            update(unsafe {
+                std::mem::transmute::<&mut AppContext, &mut MainThread<AppContext>>(cx)
+            })
+        })
+    }
+
     pub(crate) fn platform(&self) -> &dyn Platform {
         self.platform.borrow_on_main_thread()
     }
@@ -320,8 +306,7 @@ impl AppContext<MainThread> {
             let id = cx.windows.insert(None);
             let handle = WindowHandle::new(id);
             let mut window = Window::new(handle.into(), options, cx);
-            let root_view =
-                build_root_view(&mut WindowContext::mutable(cx.downcast_mut(), &mut window));
+            let root_view = build_root_view(&mut WindowContext::mutable(cx, &mut window));
             window.root_view.replace(root_view.into_any());
             cx.windows.get_mut(id).unwrap().replace(window);
             handle
diff --git a/crates/gpui3/src/app/async_context.rs b/crates/gpui3/src/app/async_context.rs
index f9c5d6f656838e79f923a504ee34bed4c9afdf8a..1f4cf537776bc4a3b4d9e1658a327b72cbd1b348 100644
--- a/crates/gpui3/src/app/async_context.rs
+++ b/crates/gpui3/src/app/async_context.rs
@@ -4,10 +4,10 @@ use parking_lot::Mutex;
 use std::sync::Weak;
 
 #[derive(Clone)]
-pub struct AsyncContext<Thread = ()>(pub(crate) Weak<Mutex<AppContext<Thread>>>);
+pub struct AsyncContext(pub(crate) Weak<Mutex<AppContext>>);
 
 impl Context for AsyncContext {
-    type EntityContext<'a, 'b, T: Send + Sync + 'static> = ModelContext<'a, T>;
+    type EntityContext<'a, 'b, T: 'static + Send + Sync> = ModelContext<'a, T>;
     type Result<T> = Result<T>;
 
     fn entity<T: Send + Sync + 'static>(
@@ -36,7 +36,7 @@ impl Context for AsyncContext {
     }
 }
 
-impl<Thread: 'static + Send + Sync> AsyncContext<Thread> {
+impl AsyncContext {
     pub fn update_window<T>(
         &self,
         handle: AnyWindowHandle,
diff --git a/crates/gpui3/src/app/model_context.rs b/crates/gpui3/src/app/model_context.rs
index 67b90db97160b5c0a5689685a42be3953e52cffd..b16d29057a60dd7aad13da24a4fb7d1eea5d7cd9 100644
--- a/crates/gpui3/src/app/model_context.rs
+++ b/crates/gpui3/src/app/model_context.rs
@@ -1,8 +1,8 @@
 use crate::{AppContext, Context, Effect, EntityId, Handle, Reference, WeakHandle};
 use std::{marker::PhantomData, sync::Arc};
 
-pub struct ModelContext<'a, T, Thread = ()> {
-    app: Reference<'a, AppContext<Thread>>,
+pub struct ModelContext<'a, T> {
+    app: Reference<'a, AppContext>,
     entity_type: PhantomData<T>,
     entity_id: EntityId,
 }
diff --git a/crates/gpui3/src/gpui3.rs b/crates/gpui3/src/gpui3.rs
index 401c69fc71564d53b2c10fa4db97377b6babc5bd..d62b42ed747edc31dcddffec669cf5fd30ea239b 100644
--- a/crates/gpui3/src/gpui3.rs
+++ b/crates/gpui3/src/gpui3.rs
@@ -45,7 +45,7 @@ pub use view::*;
 pub use window::*;
 
 pub trait Context {
-    type EntityContext<'a, 'w, T: Send + Sync + 'static>;
+    type EntityContext<'a, 'w, T: 'static + Send + Sync>;
     type Result<T>;
 
     fn entity<T: Send + Sync + 'static>(
@@ -60,6 +60,29 @@ pub trait Context {
     ) -> Self::Result<R>;
 }
 
+#[repr(transparent)]
+pub struct MainThread<T>(T);
+
+impl<T> MainThread<T> {
+    fn new(value: T) -> Self {
+        Self(value)
+    }
+}
+
+impl<T> Deref for MainThread<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for MainThread<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
 pub trait StackContext {
     fn app(&mut self) -> &mut AppContext;
 
@@ -154,8 +177,6 @@ impl<'a, T> DerefMut for Reference<'a, T> {
     }
 }
 
-pub struct MainThread;
-
 pub(crate) struct MainThreadOnly<T: ?Sized> {
     dispatcher: Arc<dyn PlatformDispatcher>,
     value: Arc<T>,
diff --git a/crates/gpui3/src/view.rs b/crates/gpui3/src/view.rs
index 7b510c6674023353304e79a1444b7a4cb03dc24a..5c7f7a766d278158c56df7a4ffec58d8ad3036fb 100644
--- a/crates/gpui3/src/view.rs
+++ b/crates/gpui3/src/view.rs
@@ -1,15 +1,14 @@
 use parking_lot::Mutex;
 
 use crate::{
-    AnyElement, Element, Handle, IntoAnyElement, Layout, LayoutId, MainThread, Result, ViewContext,
+    AnyElement, Element, Handle, IntoAnyElement, Layout, LayoutId, Result, ViewContext,
     WindowContext,
 };
 use std::{any::Any, marker::PhantomData, sync::Arc};
 
-pub struct View<S: Send + Sync, P, Thread = ()> {
+pub struct View<S: Send + Sync, P> {
     state: Handle<S>,
-    render:
-        Arc<dyn Fn(&mut S, &mut ViewContext<S, Thread>) -> AnyElement<S> + Send + Sync + 'static>,
+    render: Arc<dyn Fn(&mut S, &mut ViewContext<S>) -> AnyElement<S> + Send + Sync + 'static>,
     parent_state_type: PhantomData<P>,
 }
 
diff --git a/crates/gpui3/src/window.rs b/crates/gpui3/src/window.rs
index 85cd5d3311c85ec125f74f80ec7ae268b0ad1593..25b4dc1df1c6ccdf0b698e88596e128e5ecb804d 100644
--- a/crates/gpui3/src/window.rs
+++ b/crates/gpui3/src/window.rs
@@ -1,10 +1,9 @@
 use crate::{
     px, AnyView, AppContext, AvailableSpace, Bounds, Context, Effect, Element, EntityId, Handle,
-    LayoutId, MainThread, MainThreadOnly, Pixels, Platform, PlatformWindow, Point, Reference,
-    Scene, Size, StackContext, Style, TaffyLayoutEngine, WeakHandle, WindowOptions,
+    LayoutId, MainThread, MainThreadOnly, Pixels, PlatformWindow, Point, Reference, Scene, Size,
+    StackContext, Style, TaffyLayoutEngine, WeakHandle, WindowOptions,
 };
 use anyhow::Result;
-use derive_more::{Deref, DerefMut};
 use std::{any::TypeId, marker::PhantomData, sync::Arc};
 use util::ResultExt;
 
@@ -26,7 +25,7 @@ impl Window {
     pub fn new(
         handle: AnyWindowHandle,
         options: WindowOptions,
-        cx: &mut AppContext<MainThread>,
+        cx: &mut MainThread<AppContext>,
     ) -> Self {
         let platform_window = cx.platform().open_window(handle, options);
         let mouse_position = platform_window.mouse_position();
@@ -62,19 +61,14 @@ impl Window {
     }
 }
 
-#[derive(Deref, DerefMut)]
-pub struct WindowContext<'a, 'w, Thread = ()> {
-    thread: PhantomData<Thread>,
-    #[deref]
-    #[deref_mut]
-    app: Reference<'a, AppContext<Thread>>,
+pub struct WindowContext<'a, 'w> {
+    app: Reference<'a, AppContext>,
     window: Reference<'w, Window>,
 }
 
 impl<'a, 'w> WindowContext<'a, 'w> {
     pub(crate) fn mutable(app: &'a mut AppContext, window: &'w mut Window) -> Self {
         Self {
-            thread: PhantomData,
             app: Reference::Mutable(app),
             window: Reference::Mutable(window),
         }
@@ -157,7 +151,7 @@ impl<'a, 'w> WindowContext<'a, 'w> {
     }
 }
 
-impl WindowContext<'_, '_, MainThread> {
+impl MainThread<WindowContext<'_, '_>> {
     // todo!("implement other methods that use platform window")
     fn platform_window(&self) -> &dyn PlatformWindow {
         self.window.platform_window.borrow_on_main_thread().as_ref()
@@ -165,14 +159,14 @@ impl WindowContext<'_, '_, MainThread> {
 }
 
 impl Context for WindowContext<'_, '_> {
-    type EntityContext<'a, 'w, T: Send + Sync + 'static> = ViewContext<'a, 'w, T>;
+    type EntityContext<'a, 'w, T: 'static + Send + Sync> = ViewContext<'a, 'w, T>;
     type Result<T> = T;
 
     fn entity<T: Send + Sync + 'static>(
         &mut self,
         build_entity: impl FnOnce(&mut Self::EntityContext<'_, '_, T>) -> T,
     ) -> Handle<T> {
-        let slot = self.entities.reserve();
+        let slot = self.app.entities.reserve();
         let entity = build_entity(&mut ViewContext::mutable(
             &mut *self.app,
             &mut self.window,
@@ -196,18 +190,32 @@ impl Context for WindowContext<'_, '_> {
     }
 }
 
+impl<'a, 'w> std::ops::Deref for WindowContext<'a, 'w> {
+    type Target = AppContext;
+
+    fn deref(&self) -> &Self::Target {
+        &self.app
+    }
+}
+
+impl<'a, 'w> std::ops::DerefMut for WindowContext<'a, 'w> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.app
+    }
+}
+
 impl<S> StackContext for ViewContext<'_, '_, S> {
     fn app(&mut self) -> &mut AppContext {
-        &mut *self.app
+        &mut *self.window_cx.app
     }
 
     fn with_text_style<F, R>(&mut self, style: crate::TextStyleRefinement, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R,
     {
-        self.push_text_style(style);
+        self.window_cx.app.push_text_style(style);
         let result = f(self);
-        self.pop_text_style();
+        self.window_cx.app.pop_text_style();
         result
     }
 
@@ -215,21 +223,17 @@ impl<S> StackContext for ViewContext<'_, '_, S> {
     where
         F: FnOnce(&mut Self) -> R,
     {
-        self.push_state(state);
+        self.window_cx.app.push_state(state);
         let result = f(self);
-        self.pop_state::<T>();
+        self.window_cx.app.pop_state::<T>();
         result
     }
 }
 
-#[derive(Deref, DerefMut)]
-pub struct ViewContext<'a, 'w, S, Thread = ()> {
-    #[deref]
-    #[deref_mut]
-    window_cx: WindowContext<'a, 'w, Thread>,
+pub struct ViewContext<'a, 'w, S> {
+    window_cx: WindowContext<'a, 'w>,
     entity_type: PhantomData<S>,
     entity_id: EntityId,
-    thread: PhantomData<Thread>,
 }
 
 impl<'a, 'w, S: Send + Sync + 'static> ViewContext<'a, 'w, S> {
@@ -238,7 +242,6 @@ impl<'a, 'w, S: Send + Sync + 'static> ViewContext<'a, 'w, S> {
             window_cx: WindowContext::mutable(app, window),
             entity_id,
             entity_type: PhantomData,
-            thread: PhantomData,
         }
     }
 
@@ -290,8 +293,8 @@ impl<'a, 'w, S: Send + Sync + 'static> ViewContext<'a, 'w, S> {
     }
 }
 
-impl<'a, 'w, S: 'static> Context for ViewContext<'a, 'w, S> {
-    type EntityContext<'b, 'c, U: Send + Sync + 'static> = ViewContext<'b, 'c, U>;
+impl<'a, 'w, S> Context for ViewContext<'a, 'w, S> {
+    type EntityContext<'b, 'c, U: 'static + Send + Sync> = ViewContext<'b, 'c, U>;
     type Result<U> = U;
 
     fn entity<T2: Send + Sync + 'static>(
@@ -310,7 +313,19 @@ impl<'a, 'w, S: 'static> Context for ViewContext<'a, 'w, S> {
     }
 }
 
-impl<S> ViewContext<'_, '_, S, MainThread> {}
+impl<'a, 'w, S: 'static> std::ops::Deref for ViewContext<'a, 'w, S> {
+    type Target = WindowContext<'a, 'w>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.window_cx
+    }
+}
+
+impl<'a, 'w, S: 'static> std::ops::DerefMut for ViewContext<'a, 'w, S> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.window_cx
+    }
+}
 
 // #[derive(Clone, Copy, Eq, PartialEq, Hash)]
 slotmap::new_key_type! { pub struct WindowId; }
diff --git a/crates/storybook2/src/workspace.rs b/crates/storybook2/src/workspace.rs
index 19b3711db5353ed86d346bb4e88c819ad40da9e1..7190035f22fd85c7bcc73187dfcec3c005c55ecf 100644
--- a/crates/storybook2/src/workspace.rs
+++ b/crates/storybook2/src/workspace.rs
@@ -1,6 +1,6 @@
 use crate::{
     collab_panel::{collab_panel, CollabPanel},
-    theme::{theme, themed},
+    theme::theme,
     themes::rose_pine_dawn,
 };
 use gpui3::{