[apps] Improve app loading. (#10994)

There are two concepts of apps that we load in the harness:

- Directory apps, which is all the apps that the user can install.
- Accessible apps, which is what the user actually installed and can be
$ inserted and be used by the model. These are extracted from the tools
that are loaded through the gateway MCP.

Previously we wait for both sets of apps before returning the full apps
list. Which causes many issues because accessible apps won't be
available to the UI or the model if directory apps aren't loaded or
failed to load.

In this PR we are separating them so that accessible apps can be loaded
separately and are instantly available to be shown in the UI and to be
provided in model context. We also added an app-server event so that
clients can subscribe to also get accessible apps without being blocked
on the full app list.

- [x] Separate accessible apps and directory apps loading.
- [x] `app/list` request will also emit `app/list/updated` notifications
that app-server clients can subscribe. Which allows clients to get
accessible apps list to render in the $ menu without being blocked by
directory apps.
- [x] Cache both accessible and directory apps with 1 hour TTL to avoid
reloading them when creating new threads.
- [x] TUI improvements to redraw $ menu and /apps menu when app list is
updated.

codex-rs/app-server/README.md

@@ -700,7 +700,8 @@ Use `app/list` to fetch available apps (connectors). Each entry includes metadat
 ```json
 { "method": "app/list", "id": 50, "params": {
     "cursor": null,
-    "limit": 50
+    "limit": 50,
+    "forceRefetch": false
 } }
 { "id": 50, "result": {
     "data": [
@@ -719,6 +720,30 @@ Use `app/list` to fetch available apps (connectors). Each entry includes metadat
 } }
 ```
 
+`app/list` returns after both accessible apps and directory apps are loaded. Set `forceRefetch: true` to bypass app caches and fetch fresh data from sources. Cache entries are only replaced when those refetches succeed.
+
+The server also emits `app/list/updated` notifications whenever either source (accessible apps or directory apps) finishes loading. Each notification includes the latest merged app list.
+
+```json
+{
+  "method": "app/list/updated",
+  "params": {
+    "data": [
+      {
+        "id": "demo-app",
+        "name": "Demo App",
+        "description": "Example connector for documentation.",
+        "logoUrl": "https://example.com/demo-app.png",
+        "logoUrlDark": null,
+        "distributionChannel": null,
+        "installUrl": "https://chatgpt.com/apps/demo-app/demo-app",
+        "isAccessible": true
+      }
+    ]
+  }
+}
+```
+
 Invoke an app by inserting `$<app-slug>` in the text input. The slug is derived from the app name and lowercased with non-alphanumeric characters replaced by `-` (for example, "Demo App" becomes `$demo-app`). Add a `mention` input item (recommended) so the server uses the exact `app://<connector-id>` path rather than guessing by name.
 
 Example: