feat: add combobox filter

AGENTS.md

@@ -57,8 +57,8 @@ GPUI is a UI framework which also provides primitives for state and concurrency
 - All use of entities and UI rendering occurs on a single foreground thread.
 - `cx.spawn(async move |cx| ...)` runs on the foreground thread; from a `Context<T>` it looks like `cx.spawn(async move |this, cx| ...)`.
 - `cx.background_spawn(async move { ... })` runs work on other threads.
-- Both return a `Task<R>`; dropping it cancels the work. Prevent cancellation by awaiting, detaching deliberately, or storing the task in a field.
-- Prefer keeping a task in a field over `.detach()` when the work belongs to a view or store; a detached task outlives its owner. A finished `Task` held in a container is not reaped — drop finished handles or hold a single `Option<Task<_>>`.
+- Both return a `Task<R>`; dropping it cancels the work. Prevent cancellation by awaiting or storing the task in a field.
+- Every task tied to a component must be stored on it: `tasks: Vec<Task<_>>` or `task: Option<Task<_>>`. Never `.detach()` a component's task — a detached task outlives its owner. gpui cleans finished tasks up automatically, so just push; no retain or prune logic.
 
 ## Rendering and state