Prevent Android chats from freezing or going blank (#1989)

* fix(app): stabilize streamed chat rendering

Use deterministic Markdown AST keys and preserve unique row identities when an assistant message resumes after a tool. Keep native gesture and plan-card children correctly keyed to avoid unsupported Fabric reconciliation paths.

* fix(app): stabilize retained native panels

Keep retained workspace roots in a stable native order and make active
panels present in the selection commit. Hidden panels now stop expensive
subscriptions and animations without losing mounted state.

* fix(app): harden retained panel activity

docs/mobile-panels.md

@@ -80,6 +80,19 @@ definition, no longer eligible to begin.
   has caused native crashes.
 - The plain React wrapper owns `display: none` after settlement. This prevents a stale Fabric animated
   prop commit from resurrecting a closed overlay.
+- Hidden tabs and workspaces use `RetainedPanel`. It owns a non-collapsible native root, visibility,
+  pointer events, and the active signal consumed by `useRetainedPanelActive`.
+- Panels whose gesture wrapper already owns visibility use `RetainedPanelActivity` to provide the
+  same active signal without adding another layout root. Persistent animations, timers, polling, and
+  shared clocks must subscribe to that signal and stop when their final visible consumer leaves.
+- Retention order and render order are separate concerns. LRU metadata may change on every switch;
+  keyed retained roots must keep a stable sibling order. Moving large retained roots triggered Fabric
+  Differ failures (`addViewAt` / `removeViewAt` view reuse) on Android.
+- The newly active panel must be included in the same render that changes selection. Adding it from an
+  effect creates a committed frame where every retained panel is hidden, which is a real blank screen.
+- Do not suspend retained native subtrees with `Suspense`/`react-freeze`. Suspension changes native
+  ownership and can detach descendants. Keep the tree mounted, stabilize its subscriptions/selectors,
+  and use the retained-panel active signal to stop timers, polling, and other genuine background work.
 
 ## Tests